The previous errata for this document, are also available.
See also translations.
Copyright © 2012 W3C® (MIT, ERCIM, Keio), All Rights Reserved. W3C liability, trademark and document use rules apply.
RDF is a directed, labeled graph data format for representing information in the Web. This specification defines the syntax and semantics of the SPARQL query language for RDF. SPARQL can be used to express queries across diverse data sources, whether the data is stored natively as RDF or viewed as RDF via middleware. SPARQL contains capabilities for querying required and optional graph patterns along with their conjunctions and disjunctions. SPARQL also supports aggregation, subqueries, negation, creating values by expressions, extensible value testing, and constraining queries by source RDF graph. The results of SPARQL queries can be result sets or RDF graphs.
This section describes the status of this document at the time of its publication. Other documents may supersede this document. A list of current W3C publications and the latest revision of this technical report can be found in the W3C technical reports index at http://www.w3.org/TR/.
This document is a Last Call Working Draft. Publication as a Last Call Working Draft indicates that the SPARQL Working Group believes it has addressed all substantive issues and that the document is stable. The Working Group expects to advance this specification to Recommendation Status.
The end date of the Last Call review period is 06 February 2012, i.e., comments on this working draft are due on or before this date.
Comments on this document should be sent to public-rdf-dawg-comments@w3.org, a mailing list with a public archive. Questions and comments about SPARQL that are not related to this specification, including extensions and features, can be discussed on the mailing list public-sparql-dev@w3.org, (public archive).
Publication as a Working Draft does not imply endorsement by the W3C Membership. This is a draft document and may be updated, replaced or obsoleted by other documents at any time. It is inappropriate to cite this document as other than work in progress.
The set of SPARQL documents comprises:
The JSON result format was previously available as a Working Group Note: Serializing SPARQL Query Results in JSON and the SPARQL Query Results XML Format has not been revised by this Working Group.
The new features in SPARQL 1.1 Query are:
The following are the non-editorial changes since last publication:
STRBEFORE
, STRAFTER
, REPLACE
REGXP
to take a first argument of xsd:string and rdf:langString.DATATYPE
on language tag literals.ORDER BY
clauseAdditiveExpression: '?' => '*'
The design of the features presented here is work-in-progress and does not represent the final decisions of the working group. Implementers and application writers should not assume that the designs in this document will not change.
This document was produced by the SPARQL Working Group, which is part of the W3C Semantic Web Activity.
This document was produced by a group operating under the 5 February 2004 W3C Patent Policy. W3C maintains a public list of any patent disclosures made in connection with the deliverables of the group; that page also includes instructions for disclosing a patent. An individual who has actual knowledge of a patent which the individual believes contains Essential Claim(s) must disclose the information in accordance with section 6 of the W3C Patent Policy.
1 Introduction
1.1 Document Outline
1.2 Document Conventions
1.2.1 Namespaces
1.2.2 Data Descriptions
1.2.3 Result Descriptions
1.2.4 Terminology
2 Making Simple Queries (Informative)
2.1 Writing a Simple Query
2.2 Multiple Matches
2.3 Matching RDF Literals
2.3.1 Matching Literals with Language Tags
2.3.2 Matching Literals with Numeric Types
2.3.3 Matching Literals with Arbitrary Datatypes
2.4 Blank Node Labels in Query Results
2.5 Creating Values with Expressions
2.6 Building RDF Graphs
3 RDF Term Constraints (Informative)
3.1 Restricting the Value of Strings
3.2 Restricting Numeric Values
3.3 Other Term Constraints
4 SPARQL Syntax
4.1 RDF Term Syntax
4.1.1 Syntax for IRIs
4.1.1.1 Prefixed Names
4.1.1.2 Relative IRIs
4.1.2 Syntax for Literals
4.1.3 Syntax for Query Variables
4.1.4 Syntax for Blank Nodes
4.2 Syntax for Triple Patterns
4.2.1 Predicate-Object Lists
4.2.2 Object Lists
4.2.3 RDF Collections
4.2.4 rdf:type
5 Graph Patterns
5.1 Basic Graph Patterns
5.1.1 Blank Node Labels
5.1.2 Extending Basic Graph Pattern Matching
5.2 Group Graph Patterns
5.2.1 Empty Group Pattern
5.2.2 Scope of Filters
5.2.3 Group Graph Pattern Examples
6 Including Optional Values
6.1 Optional Pattern Matching
6.2 Constraints
in Optional Pattern Matching
6.3 Multiple Optional Graph
Patterns
7 Matching Alternatives
8 Negation
8.1 Filtering Using Graph Patterns
8.1.1 Testing For the Absence of a Pattern
8.1.2 Testing For the Presence of a Pattern
8.2 Removing Possible Solutions
8.3 Relationship and differences between NOT EXISTS and MINUS
8.3.1 Example: Sharing of variables
8.3.2 Example: Fixed pattern
8.3.3 Example: Inner FILTERs
9 Property Paths
9.1 Property Path Syntax
9.2 Examples
9.3 Cycles and Duplicates
10 Assignment
10.1 BIND: Assigning to Variables
10.2 BINDINGS
11 Aggregates
11.1 Aggregate Example
11.2 GROUP BY
11.3 HAVING
11.4 Aggregate Projection Restrictions
11.5 Aggregate Example (with errors)
12 Subqueries
13 RDF Dataset
13.1 Examples of RDF Datasets
13.2 Specifying RDF Datasets
13.2.1 Specifying the Default Graph
13.2.2 Specifying Named Graphs
13.2.3 Combining FROM and FROM NAMED
13.3 Querying the Dataset
13.3.1 Accessing Graph Names
13.3.2 Restricting by Graph
IRI
13.3.3 Restricting Possible Graph IRIs
13.3.4 Named and Default
Graphs
14 Basic Federated Query
15 Solution Sequences and Modifiers
15.1 ORDER BY
15.2 Projection
15.3 Duplicate Solutions
15.4 OFFSET
15.5 LIMIT
16 Query Forms
16.1 SELECT
16.1.1 Projection
16.1.2 SELECT Expressions
16.2 CONSTRUCT
16.2.1 Templates with Blank Nodes
16.2.2 Accessing Graphs in the RDF Dataset
16.2.3 Solution Modifiers and CONSTRUCT
16.2.4 CONSTRUCT WHERE
16.3 ASK
16.4 DESCRIBE (Informative)
16.4.1 Explicit IRIs
16.4.2 Identifying Resources
16.4.3 Descriptions of Resources
17 Expressions and Testing Values
17.1 Operand Data Types
17.2 Filter Evaluation
17.2.1 Invocation
17.2.2 Effective Boolean Value (EBV)
17.3 Operator Mapping
17.3.1 Operator Extensibility
17.4 Function Definitions
17.4.1 Functional Forms
17.4.1.1 bound
17.4.1.2 IF
17.4.1.3 COALESCE
17.4.1.4 NOT EXISTS and EXISTS
17.4.1.5 logical-or
17.4.1.6 logical-and
17.4.1.7 RDFterm-equal
17.4.1.8 sameTerm
17.4.1.9 IN
17.4.1.10 NOT IN
17.4.2 Functions on RDF Terms
17.4.2.1 isIRI
17.4.2.2 isBlank
17.4.2.3 isLiteral
17.4.2.4 isNumeric
17.4.2.5 str
17.4.2.6 lang
17.4.2.7 datatype
17.4.2.8 IRI
17.4.2.9 BNODE
17.4.2.10 STRDT
17.4.2.11 STRLANG
17.4.3 Functions on Strings
17.4.3.1 Strings in SPARQL Functions
17.4.3.1.1 String arguments
17.4.3.1.2 Argument Compatibility Rules
17.4.3.1.3 String Literal Return Type
17.4.3.2 STRLEN
17.4.3.3 SUBSTR
17.4.3.4 UCASE
17.4.3.5 LCASE
17.4.3.6 STRSTARTS
17.4.3.7 STRENDS
17.4.3.8 CONTAINS
17.4.3.9 STRBEFORE
17.4.3.10 STRAFTER
17.4.3.11 ENCODE_FOR_URI
17.4.3.12 CONCAT
17.4.3.13 langMatches
17.4.3.14 REGEX
17.4.3.15 REPLACE
17.4.4 Functions on Numerics
17.4.4.1 abs
17.4.4.2 round
17.4.4.3 ceil
17.4.4.4 floor
17.4.4.5 RAND
17.4.5 Functions on Dates and Times
17.4.5.1 now
17.4.5.2 year
17.4.5.3 month
17.4.5.4 day
17.4.5.5 hours
17.4.5.6 minutes
17.4.5.7 seconds
17.4.5.8 timezone
17.4.5.9 tz
17.4.6 Hash Functions
17.4.6.1 MD5
17.4.6.2 SHA1
17.4.6.3 SHA256
17.4.6.4 SHA384
17.4.6.5 SHA512
17.5 XPath Constructor Functions
17.6 Extensible Value Testing
18 Definition of SPARQL
18.1 Initial Definitions
18.1.1 RDF Terms
18.1.2 Simple Literal
18.1.3 RDF Dataset
18.1.4 Query Variables
18.1.5 Triple Patterns
18.1.6 Basic Graph Patterns
18.1.7 Property Path Patterns
18.1.8 Solution Mapping
18.1.9 Solution Sequence Modifiers
18.1.10 SPARQL Query
18.2 Translation to the SPARQL Algebra
18.2.1 Variable Scope
18.2.2 Converting Graph Patterns
18.2.2.1 Expand Syntax Forms
18.2.2.2 Translate Property Path Expressions
18.2.2.3 Translate Basic Graph Patterns
18.2.2.4 Translate Patterns in Filters
18.2.2.5 Translate Graph Patterns
18.2.2.6 Simplification step
18.2.3 Examples of Mapped Graph Patterns
18.2.4 Converting Groups, Aggregates, HAVING, BINDINGS and SELECT Expressions
18.2.4.1 Grouping and Aggregation
18.2.4.2 HAVING
18.2.4.3 BINDINGS
18.2.4.4 SELECT Expressions
18.2.5 Converting Solution Modifiers
18.2.5.1 ORDER BY
18.2.5.2 Projection
18.2.5.3 DISTINCT
18.2.5.4 REDUCED
18.2.5.5 OFFSET and LIMIT
18.2.5.6 Final Algebra Expression
18.3 Basic Graph Patterns
18.3.1 SPARQL Basic Graph Pattern Matching
18.3.2 Treatment of Blank Nodes
18.4 SPARQL Algebra
18.4.1 Aggregate Algebra
18.4.1.1 Set Functions
18.4.1.2 Count
18.4.1.3 Sum
18.4.1.4 Avg
18.4.1.5 Min
18.4.1.6 Max
18.4.1.7 GroupConcat
18.4.1.8 Sample
18.5 Evaluation Semantics
18.6 Extending SPARQL Basic Graph Matching
18.6.1 Notes
19 SPARQL Grammar
19.1 SPARQL Query String
19.2 Codepoint Escape Sequences
19.3 White Space
19.4 Comments
19.5 IRI References
19.6 Blank Node Labels
19.7 Escape sequences in strings
19.8 Grammar
20 Conformance
21 Security Considerations (Informative)
22 Internet Media Type, File Extension and Macintosh File Type
A References
A.1 Normative References
A.2 Other References
B CVS History (Last Call and after)
RDF is a directed, labeled graph data format for representing information in the Web. RDF is often used to represent, among other things, personal information, social networks, metadata about digital artifacts, as well as to provide a means of integration over disparate sources of information. This specification defines the syntax and semantics of the SPARQL query language for RDF.
The SPARQL query language for RDF is designed to meet the use cases and requirements identified by the RDF Data Access Working Group in RDF Data Access Use Cases and Requirements [UCNR] and SPARQL New Features and Rationale [UCNR2].
Unless otherwise noted in the section heading, all sections and appendices in this document are normative.
This section of the document, section 1, introduces the SPARQL query language specification. It presents the organization of this specification document and the conventions used throughout the specification.
Section 2 of the specification introduces the SPARQL query language itself via a series of example queries and query results. Section 3 continues the introduction of the SPARQL query language with more examples that demonstrate SPARQL's ability to express constraints on the RDF terms that appear in a query's results.
Section 4 presents details of the SPARQL query language's syntax. It is a companion to the full grammar of the language and defines how grammatical constructs represent IRIs, blank nodes, literals, and variables. Section 4 also defines the meaning of several grammatical constructs that serve as syntactic sugar for more verbose expressions.
Section 5 introduces basic graph patterns and group graph patterns, the building blocks from which more complex SPARQL query patterns are constructed. Sections 6, 7, and 8 present constructs that combine SPARQL graph patterns into larger graph patterns. In particular, Section 6 introduces the ability to make portions of a query optional; Section 7 introduces the ability to express the disjunction of alternative graph patterns; and Section 8 introduces patterns to test for the absense of information.
Section 9 adds property paths to graph pattern matching, giving a compact representation of queries and also the ability to match arbitrary length paths in the graph.
Section 10 describes the forms of assignment possible in SPARQL.
Sections 11 introduces the mechanism to group and aggregate results, which can be incorporated as subqueries as described in Section 12.
Section 13 introduces the ability to constrain portions of a query to particular source graphs. Section 13 also presents SPARQL's mechanism for defining the source graphs for a query.
Section 14 refers to the separate document SPARQL 1.1 Federated Query.
Section 15 defines the constructs that affect the solutions of a query by ordering, slicing, projecting, limiting, and removing duplicates from a sequence of solutions.
Section 16 defines the four types of SPARQL queries that produce results in different forms.
Section 17 defines SPARQL's extensible value testing and expression framework. It presents the functions and operators that can be used to constrain the values that appear in a query's results and also calculate new values to be returned by a query.
Section 18 is a formal definition of the evaluation of SPARQL graph patterns and solution modifiers.
Section 19 contains the normative definition of the syntax for the SPARQL query and SPARQL update languages, as given by a grammar expressed in EBNF notation.
In this document, examples assume the following namespace prefix bindings unless otherwise stated:
Prefix | IRI |
---|---|
rdf: | http://www.w3.org/1999/02/22-rdf-syntax-ns# |
rdfs: | http://www.w3.org/2000/01/rdf-schema# |
xsd: | http://www.w3.org/2001/XMLSchema# |
fn: | http://www.w3.org/2005/xpath-functions# |
sfn: | http://www.w3.org/ns/sparql# @@(process) Ensure page populated (see
this list). |
This document uses the Turtle [TURTLE] data format to show each triple explicitly. Turtle allows IRIs to be abbreviated with prefixes:
@prefix dc: <http://purl.org/dc/elements/1.1/> . @prefix : <http://example.org/book/> . :book1 dc:title "SPARQL Tutorial" .
Result sets are illustrated in tabular form.
A 'binding' is a pair (variable,
RDF term). In this result set, there are three
variables:
x
, y
and z
(shown as column headers). Each
solution is shown as one row in the body of the table. Here, there is a single
solution, in which variable x
is bound to "Alice"
, variable
y
is bound to <http://example/a>
, and variable z
is not bound to an RDF term. Variables are not required to be bound in a
solution.
The SPARQL language includes IRIs, a subset of RDF URI References that omits spaces. Note that all IRIs in SPARQL queries are absolute; they may or may not include a fragment identifier [RFC3987, section 3.1]. IRIs include URIs [RFC3986] and URLs. The abbreviated forms (relative IRIs and prefixed names) in the SPARQL syntax are resolved to produce absolute IRIs.
The following terms are defined in RDF Concepts and Abstract Syntax [CONCEPTS] and used in SPARQL:
RDF URI reference
")datatype URI
")In addition, we define the following terms:
Most forms of SPARQL query contain a set of triple patterns called a basic graph pattern. Triple patterns are like RDF triples except that each of the subject, predicate and object may be a variable. A basic graph pattern matches a subgraph of the RDF data when RDF terms from that subgraph may be substituted for the variables and the result is RDF graph equivalent to the subgraph.
The example below shows a SPARQL query to find the title of a book from the
given data graph. The query consists of two parts:
the SELECT
clause identifies
the variables to appear in the query results, and the WHERE
clause
provides the basic graph pattern to match against the data graph. The basic graph pattern in this example
consists of a single triple pattern with a single variable (?title
) in the object position.
The result of a query is a solution sequence, corresponding to the ways in which the query's graph pattern matches the data. There may be zero, one or multiple solutions to a query.
Data:
@prefix foaf: <http://xmlns.com/foaf/0.1/> . _:a foaf:name "Johnny Lee Outlaw" . _:a foaf:mbox <mailto:jlow@example.com> . _:b foaf:name "Peter Goodguy" . _:b foaf:mbox <mailto:peter@example.org> . _:c foaf:mbox <mailto:carol@example.org> .
Query:
PREFIX foaf: <http://xmlns.com/foaf/0.1/> SELECT ?name ?mbox WHERE { ?x foaf:name ?name . ?x foaf:mbox ?mbox }
Query Result:
name | mbox |
---|---|
"Johnny Lee Outlaw" | <mailto:jlow@example.com> |
"Peter Goodguy" | <mailto:peter@example.org> |
Each solution gives one way in which the selected variables can be bound to RDF terms so that the query pattern matches the data. The result set gives all the possible solutions. In the above example, the following two subsets of the data provided the two matches.
_:a foaf:name "Johnny Lee Outlaw" . _:a foaf:box <mailto:jlow@example.com> .
_:b foaf:name "Peter Goodguy" . _:b foaf:box <mailto:peter@example.org> .
This is a basic graph pattern match; all the variables used in the query pattern must be bound in every solution.
The data below contains three RDF literals:
@prefix dt: <http://example.org/datatype#> .
@prefix ns: <http://example.org/ns#> .
@prefix : <http://example.org/ns#> .
@prefix xsd: <http://www.w3.org/2001/XMLSchema#> .
:x ns:p "cat"@en .
:y ns:p "42"^^xsd:integer .
:z ns:p "abc"^^dt:specialDatatype .
Note that, in Turtle, "cat"@en
is an RDF literal with a lexical form "cat" and a language tag "en"; "42"^^xsd:integer
is a typed literal with the datatype http://www.w3.org/2001/XMLSchema#integer
; and "abc"^^dt:specialDatatype
is a typed literal with the datatype http://example.org/datatype#specialDatatype
.
This RDF data is the data graph for the query examples in sections 2.3.1–2.3.3.
Language tags in SPARQL are expressed using @
and the
language tag, as defined in Best Common Practice 47 [BCP47].
This following query has no solution because "cat"
is not the
same RDF literal as "cat"@en
:
SELECT ?v WHERE { ?v ?p "cat" }
v |
---|
but the query below will find a solution where variable v
is bound to
:x
because the language tag is specified and matches the given data:
SELECT ?v WHERE { ?v ?p "cat"@en }
v |
---|
<http://example.org/ns#x> |
Integers in a SPARQL query indicate an RDF typed literal with the datatype
xsd:integer
. For example: 42
is a shortened form
of "42"^^<http://www.w3.org/2001/XMLSchema#integer>
.
The pattern in the following query has a solution with variable v
bound to :y
.
Section 4.1.2 defines SPARQL shortened forms for xsd:float
and xsd:double
.
Query results can contain blank nodes. Blank nodes in the example result sets in this document are written in the form "_:" followed by a blank node label.
Blank node labels are scoped to a result set (see
"SPARQL
Query Results XML Format" and
"SPARQL 1.1 Query Results JSON Format")
or, for the CONSTRUCT
query
form, the result graph.
Use of the same label within a
result set indicates the same blank node.
@prefix foaf: <http://xmlns.com/foaf/0.1/> . _:a foaf:name "Alice" . _:b foaf:name "Bob" .
PREFIX foaf: <http://xmlns.com/foaf/0.1/> SELECT ?x ?name WHERE { ?x foaf:name ?name }
The results above could equally be given with different blank node labels because the labels in the results only indicate whether RDF terms in the solutions are the same or different.
These two results have the same information: the blank nodes used to match the
query are different in the two solutions. There need not be any relation between a
label
_:a
in the result set and a blank node in the data graph
with the same label.
An application writer should not expect blank node labels in a query to refer to a particular blank node in the data.
SPARQL 1.1 allows to create values from complex expressions.
The queries below show how to the CONCAT function
can be used to concatenate first names and last names from foaf data, then assign
the value using an expression in the SELECT
clause
and also assign the value by using the BIND form.
@prefix foaf: <http://xmlns.com/foaf/0.1/> . _:a foaf:givenName "John" . _:a foaf:surname "Doe" .
SPARQL has several query forms.
The SELECT
query form
returns variable bindings. The CONSTRUCT
query form
returns an RDF graph. The graph is built based on a template
which is used to generate RDF triples based on the results of matching
the graph pattern of the query.
Data:
@prefix org: <http://example.com/ns#> . _:a org:employeeName "Alice" . _:a org:employeeId 12345 . _:b org:employeeName "Bob" . _:b org:employeeId 67890 .
Query:
PREFIX foaf: <http://xmlns.com/foaf/0.1/> PREFIX org: <http://example.com/ns#> CONSTRUCT { ?x foaf:name ?name } WHERE { ?x org:employeeName ?name }
Results:
@prefix foaf: <http://xmlns.com/foaf/0.1/> . _:x foaf:name "Alice" . _:y foaf:name "Bob" .
which can be serialized in RDF/XML as:
<rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#" xmlns:foaf="http://xmlns.com/foaf/0.1/" > <rdf:Description> <foaf:name>Alice</foaf:name> </rdf:Description> <rdf:Description> <foaf:name>Bob</foaf:name> </rdf:Description> </rdf:RDF>
Graph pattern matching produces a solution sequence, where each solution has a set of bindings of variables to RDF terms. SPARQL FILTER
s
restrict solutions to those for which the filter expression evaluates to TRUE
.
This section provides an informal introduction to SPARQL FILTER
s; their semantics are defined in section 'Expressions and Testing Values' where there is a comprehensive function library. The examples in this section share one input graph:
@prefix dc: <http://purl.org/dc/elements/1.1/> . @prefix : <http://example.org/book/> . @prefix ns: <http://example.org/ns#> . :book1 dc:title "SPARQL Tutorial" . :book1 ns:price 42 . :book2 dc:title "The Semantic Web" . :book2 ns:price 23 .
SPARQL FILTER
functions like regex
can test RDF literals. regex
matches only string literals.
regex
can be used to match the lexical forms of other literals by
using the str
function.
Query:
PREFIX dc: <http://purl.org/dc/elements/1.1/> SELECT ?title WHERE { ?x dc:title ?title FILTER regex(?title, "^SPARQL") }
Query Result:
Regular expression matches may be made case-insensitive with the "i
"
flag.
Query:
PREFIX dc: <http://purl.org/dc/elements/1.1/> SELECT ?title WHERE { ?x dc:title ?title FILTER regex(?title, "web", "i" ) }
Query Result:
The regular expression language is defined by XQuery 1.0 and XPath 2.0 Functions and Operators and is based on XML Schema Regular Expressions.
By constraining the price
variable, only :book2
matches
the query because only :book2
has a price less than 30.5
,
as the filter condition requires.
In addition to numeric types, SPARQL supports
types xsd:string
, xsd:boolean
and xsd:dateTime
(see Operand Data Types).
Section Operator Mapping describes the operators
and section Function Definitions the functions that can be
that can be applied to RDF terms.
This section covers the syntax used by SPARQL for RDF terms and triple patterns. The full grammar is given in section 19.
The IRIref production designates the set of IRIs [RFC3987]; IRIs are a generalization of URIs [RFC3986] and are fully compatible with URIs and URLs. The PrefixedName production designates a prefixed name. The mapping from a prefixed name to an IRI is described below. IRI references (relative or absolute IRIs) are designated by the IRI_REF production, where the '<' and '>' delimiters do not form part of the IRI reference. Relative IRIs match the irelative-ref
reference in section 2.2 ABNF for IRI References and IRIs in [RFC3987] and are resolved to IRIs as described below.
The set of RDF terms defined in RDF Concepts and Abstract Syntax
includes RDF URI references while SPARQL terms include IRIs. RDF URI
references containing "<
", ">
", '"
' (double
quote), space, "{
", "}
", "|
",
"\
", "^
", and
"`
" are not IRIs. The behavior of a SPARQL query against RDF
statements composed of such RDF URI references is not defined.
The PREFIX
keyword associates a prefix label with an IRI. A prefixed
name is a prefix label and a local part, separated by a colon ":
".
A prefixed name is mapped to an IRI by concatenating the IRI associated with the prefix and the local part.
The prefix label or the local part may be empty.
Note that SPARQL local names allow leading digits while XML local names do not.
SPARQL local names also allow the non-alphanumeric characters allowed in IRIs
via backslash character escapes (e.g. ns:id\=123
).
SPARQL local names have more syntactic restrictions than CURIEs.
Relative IRIs are combined with base IRIs as per Uniform Resource Identifier (URI): Generic Syntax [RFC3986] using only the basic algorithm in section 5.2. Neither Syntax-Based Normalization nor Scheme-Based Normalization (described in sections 6.2.2 and 6.2.3 of RFC3986) are performed. Characters additionally allowed in IRI references are treated in the same way that unreserved characters are treated in URI references, per section 6.5 of Internationalized Resource Identifiers (IRIs) [RFC3987].
The BASE
keyword defines the Base IRI used to resolve relative IRIs
per RFC3986 section 5.1.1, "Base URI Embedded in Content". Section 5.1.2, "Base
URI from the Encapsulating Entity" defines how the Base IRI may come from an encapsulating
document, such as a SOAP envelope with an xml:base directive or a mime multipart
document with a Content-Location header. The "Retrieval URI" identified in 5.1.3,
Base "URI from the Retrieval URI", is the URL from which a particular SPARQL query
was retrieved. If none of the above specifies the Base URI, the default Base URI
(section 5.1.4, "Default Base URI") is used.
The following fragments are some of the different ways to write the same IRI:
<http://example.org/book/book1>
BASE <http://example.org/book/> <book1>
PREFIX book: <http://example.org/book/> book:book1
The general syntax for literals is a string (enclosed in either double
quotes, "..."
, or single quotes, '...'
), with either an optional
language tag (introduced by @
) or an optional datatype IRI or prefixed
name (introduced by ^^
).
As a convenience, integers can be written directly (without quotation marks and an explicit datatype IRI) and are interpreted as typed
literals of datatype xsd:integer
; decimal numbers for which there is '.'
in the number but no exponent are interpreted as xsd:decimal
; and
numbers with exponents are interpreted as xsd:double
. Values of
type xsd:boolean
can also be written as true
or
false
.
To facilitate writing literal values which themselves contain quotation marks or which are long and contain newline characters, SPARQL provides an additional quoting construct in which literals are enclosed in three single- or double-quotation marks.
Examples of literal syntax in SPARQL include:
"chat"
'chat'@fr
with language tag "fr""xyz"^^<http://example.org/ns/userDatatype>
"abc"^^appNS:appDataType
'''The librarian said, "Perhaps you would enjoy 'War and Peace'."'''
1
, which is the same as "1"^^xsd:integer
1.3
, which is the same as "1.3"^^xsd:decimal
1.300
, which is the same as "1.300"^^xsd:decimal
1.0e6
, which is the same as "1.0e6"^^xsd:double
true
, which is the same as "true"^^xsd:boolean
false
, which is the same as "false"^^xsd:boolean
Tokens matching the productions INTEGER, DECIMAL, DOUBLE and
BooleanLiteral are equivalent to a typed
literal with the lexical value of the token and the corresponding
datatype (xsd:integer
, xsd:decimal
, xsd:double
, xsd:boolean
).
A query variable is marked by the use of either "?" or "$";
the "?" or "$" is not part of the variable name.
In a query, $abc
and ?abc
identify the same variable. The
possible names for variables are given in the
SPARQL grammar.
Blank nodes in graph patterns act as variables, not as references to specific blank nodes in the data being queried.
Blank nodes are indicated by either the label form, such as "_:abc
", or the abbreviated form "[]
". A blank
node that is used in only one place in the query syntax can be indicated with
[]
. A unique blank node will be used to form the triple
pattern. Blank node labels are written as "_:abc
" for a blank node with
label "abc
". The same blank node label cannot be used
in two different basic graph patterns in the same query.
The [:p :v]
construct can be used in triple patterns. It creates
a blank node label which is used as the subject of all contained predicate-object
pairs. The created blank node can also be used in further triple patterns in the
subject and object positions.
The following two forms
[ :p "v" ] .
[] :p "v" .
allocate a unique blank node label (here "b57
") and are equivalent
to writing:
_:b57 :p "v" .
This allocated blank node label can be used as the subject or object of further triple patterns. For example, as a subject:
[ :p "v" ] :q "w" .
which is equivalent to the two triples:
_:b57 :p "v" . _:b57 :q "w" .
and as an object:
:x :q [ :p "v" ] .
which is equivalent to the two triples:
:x :q _:b57 . _:b57 :p "v" .
Abbreviated blank node syntax can be combined with other abbreviations for common subjects and common predicates.
[ foaf:name ?name ; foaf:mbox <mailto:alice@example.org> ]
This is the same as writing the following basic graph pattern for some uniquely
allocated blank node label, "b18
":
_:b18 foaf:name ?name . _:b18 foaf:mbox <mailto:alice@example.org> .
Triple Patterns are written as subject, predicate and object; there are abbreviated ways of writing some common triple pattern constructs.
The following examples express the same query:
PREFIX dc: <http://purl.org/dc/elements/1.1/> SELECT ?title WHERE { <http://example.org/book/book1> dc:title ?title }
PREFIX dc: <http://purl.org/dc/elements/1.1/> PREFIX : <http://example.org/book/> SELECT $title WHERE { :book1 dc:title $title }
BASE <http://example.org/book/> PREFIX dc: <http://purl.org/dc/elements/1.1/> SELECT $title WHERE { <book1> dc:title ?title }
Triple patterns with a common subject can be written so that the subject is only
written once and is used for more than one triple pattern by employing the ";
"
notation.
?x foaf:name ?name ; foaf:mbox ?mbox .
This is the same as writing the triple patterns:
?x foaf:name ?name . ?x foaf:mbox ?mbox .
If triple patterns share both subject and predicate, the objects may be separated
by ",
".
?x foaf:nick "Alice" , "Alice_" .
is the same as writing the triple patterns:
?x foaf:nick "Alice" . ?x foaf:nick "Alice_" .
Object lists can be combined with predicate-object lists:
?x foaf:name ?name ; foaf:nick "Alice" , "Alice_" .
is equivalent to:
?x foaf:name ?name . ?x foaf:nick "Alice" . ?x foaf:nick "Alice_" .
RDF collections can be written in triple patterns using the syntax "(element1 element2 ...)". The
form "()
" is an alternative for the IRI
http://www.w3.org/1999/02/22-rdf-syntax-ns#nil
.
When used with collection elements, such as (1 ?x 3 4)
, triple patterns
with blank nodes are allocated for the collection. The blank node at the head
of the collection can be used as a subject or object in other triple patterns. The blank nodes allocated by the collection syntax do not occur elsewhere in the query.
(1 ?x 3 4) :p "w" .
is syntactic sugar for (noting that b0
, b1
, b2
and b3
do not occur anywhere else in the
query):
_:b0 rdf:first 1 ; rdf:rest _:b1 . _:b1 rdf:first ?x ; rdf:rest _:b2 . _:b2 rdf:first 3 ; rdf:rest _:b3 . _:b3 rdf:first 4 ; rdf:rest rdf:nil . _:b0 :p "w" .
RDF collections can be nested and can involve other syntactic forms:
(1 [:p :q] ( 2 ) ) .
is syntactic sugar for:
_:b0 rdf:first 1 ; rdf:rest _:b1 . _:b1 rdf:first _:b2 . _:b2 :p :q . _:b1 rdf:rest _:b3 . _:b3 rdf:first _:b4 . _:b4 rdf:first 2 ; rdf:rest rdf:nil . _:b3 rdf:rest rdf:nil .
The keyword "a
" can be used as a predicate in a triple pattern and
is an alternative for the IRI
http://www.w3.org/1999/02/22-rdf-syntax-ns#type
.
This keyword is case-sensitive.
?x a :Class1 . [ a :appClass ] :p "v" .
is syntactic sugar for:
?x rdf:type :Class1 . _:b0 rdf:type :appClass . _:b0 :p "v" .
SPARQL is based around graph pattern matching. More complex graph patterns can be formed by combining smaller patterns in various ways:
In this section we describe the two forms that combine patterns by conjunction: basic graph patterns, which combine triples patterns, and group graph patterns, which combine all other graph patterns.
The outer-most graph pattern in a query is called the query pattern. It is grammatically identified by GroupGraphPattern
in
[17] | WhereClause | ::= | 'WHERE'? GroupGraphPattern |
Basic graph patterns are sets of triple patterns. SPARQL graph pattern matching is defined in terms of combining the results from matching basic graph patterns.
A sequence of triple patterns, with optional filters, comprises a single basic graph pattern. Any other graph pattern terminates a basic graph pattern.
When using blank nodes of the form _:abc
, labels for blank
nodes are scoped to the basic graph pattern. A label can be used in only a
single basic graph pattern in any query.
SPARQL evaluates basic graph patterns using subgraph matching, which is defined for simple entailment. SPARQL can be extended to other forms of entailment given certain conditions as described below. The document SPARQL 1.1 Entailment Regimes describes several specific entailment regimes.
In a SPARQL query string, a group graph pattern is delimited with braces:
{}
. For example, this query's query pattern is a group graph pattern of one basic
graph pattern.
PREFIX foaf: <http://xmlns.com/foaf/0.1/> SELECT ?name ?mbox WHERE { ?x foaf:name ?name . ?x foaf:mbox ?mbox . }
PREFIX foaf: <http://xmlns.com/foaf/0.1/> SELECT ?name ?mbox WHERE { { ?x foaf:name ?name . } { ?x foaf:mbox ?mbox . } }
The group pattern:
{ }
matches any graph (including the empty graph) with one solution that does not bind any variables. For example:
SELECT ?x WHERE {}
matches with one solution in which variable x
is not bound.
A constraint, expressed by the keyword FILTER
, is a
restriction on solutions over the whole group in which the filter appears. The
following patterns all have the same solutions:
{ ?x foaf:name ?name . ?x foaf:mbox ?mbox . FILTER regex(?name, "Smith") }
{ FILTER regex(?name, "Smith") ?x foaf:name ?name . ?x foaf:mbox ?mbox . }
{ ?x foaf:name ?name . FILTER regex(?name, "Smith") ?x foaf:mbox ?mbox . }
{ ?x foaf:name ?name . ?x foaf:mbox ?mbox . }
is a group of one basic graph pattern and that basic graph pattern consists of two triple patterns.
{ ?x foaf:name ?name . FILTER regex(?name, "Smith") ?x foaf:mbox ?mbox . }
is a group of one basic graph pattern and a filter, and that basic graph pattern consists of two triple patterns; the filter does not break the basic graph pattern into two basic graph patterns.
{ ?x foaf:name ?name . {} ?x foaf:mbox ?mbox . }
is a group of three elements, a basic graph pattern of one triple pattern, an empty group, and another basic graph pattern of one triple pattern.
Basic graph patterns allow applications to make queries where the entire query pattern must match for there to be a solution. For every solution of a query containing only group graph patterns with at least one basic graph pattern, every variable is bound to an RDF Term in a solution. However, regular, complete structures cannot be assumed in all RDF graphs. It is useful to be able to have queries that allow information to be added to the solution where the information is available, but do not reject the solution because some part of the query pattern does not match. Optional matching provides this facility: if the optional part does not match, it creates no bindings but does not eliminate the solution.
Optional parts of the graph pattern may be specified syntactically with the OPTIONAL keyword applied to a graph pattern:
pattern OPTIONAL { pattern }
The syntactic form:
{ OPTIONAL { pattern } }
is equivalent to:
{ { } OPTIONAL { pattern } }
The OPTIONAL
keyword is left-associative :
pattern OPTIONAL { pattern } OPTIONAL { pattern }
is the same as:
{ pattern OPTIONAL { pattern } } OPTIONAL { pattern }
In an optional match, either the optional graph pattern matches a graph, thereby defining and adding bindings to one or more solutions, or it leaves a solution unchanged without adding any additional bindings.
Data:
@prefix foaf: <http://xmlns.com/foaf/0.1/> . @prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> . _:a rdf:type foaf:Person . _:a foaf:name "Alice" . _:a foaf:mbox <mailto:alice@example.com> . _:a foaf:mbox <mailto:alice@work.example> . _:b rdf:type foaf:Person . _:b foaf:name "Bob" .
There is no value of mbox
in the solution where the name is
"Bob"
.
This query finds the names of people in the data. If there is a triple with predicate
mbox
and the same subject, a solution will contain the object of that triple
as well. In this example, only a single triple pattern is given in the optional match
part of the query but, in general, the optional part may be any graph pattern. The entire
optional graph pattern must match for the optional graph pattern to affect
the query solution.
Constraints can be given in an optional graph pattern. For example:
@prefix dc: <http://purl.org/dc/elements/1.1/> . @prefix : <http://example.org/book/> . @prefix ns: <http://example.org/ns#> . :book1 dc:title "SPARQL Tutorial" . :book1 ns:price 42 . :book2 dc:title "The Semantic Web" . :book2 ns:price 23 .
No price appears for the book with title "SPARQL Tutorial" because the optional
graph pattern did not lead to a solution involving the variable "price
".
Graph patterns are defined recursively. A graph pattern may have zero or more optional graph patterns, and any part of a query pattern may have an optional part. In this example, there are two optional graph patterns.
@prefix foaf: <http://xmlns.com/foaf/0.1/> . _:a foaf:name "Alice" . _:a foaf:homepage <http://work.example.org/alice/> . _:b foaf:name "Bob" . _:b foaf:mbox <mailto:bob@work.example> .
SPARQL provides a means of combining graph patterns so that one of several alternative graph patterns may match. If more than one of the alternatives matches, all the possible pattern solutions are found.
Pattern alternatives are syntactically specified with the UNION
keyword.
@prefix dc10: <http://purl.org/dc/elements/1.0/> . @prefix dc11: <http://purl.org/dc/elements/1.1/> . _:a dc10:title "SPARQL Query Language Tutorial" . _:a dc10:creator "Alice" . _:b dc11:title "SPARQL Protocol Tutorial" . _:b dc11:creator "Bob" . _:c dc10:title "SPARQL" . _:c dc11:title "SPARQL (updated)" .
PREFIX dc10: <http://purl.org/dc/elements/1.0/> PREFIX dc11: <http://purl.org/dc/elements/1.1/> SELECT ?title WHERE { { ?book dc10:title ?title } UNION { ?book dc11:title ?title } }
Query result:
This query finds titles of the books in the data, whether the title is recorded using Dublin Core properties from version 1.0 or version 1.1. To determine exactly how the information was recorded, a query could use different variables for the two alternatives:
PREFIX dc10: <http://purl.org/dc/elements/1.0/> PREFIX dc11: <http://purl.org/dc/elements/1.1/> SELECT ?x ?y WHERE { { ?book dc10:title ?x } UNION { ?book dc11:title ?y } }
This will return results with the variable x
bound for solutions from the left branch of the UNION
, and y
bound
for the solutions from the right branch. If neither part of the UNION
pattern matched, then the graph pattern would not match.
The UNION
pattern combines graph patterns; each alternative possibility can contain more
than one triple
pattern:
PREFIX dc10: <http://purl.org/dc/elements/1.0/> PREFIX dc11: <http://purl.org/dc/elements/1.1/> SELECT ?title ?author WHERE { { ?book dc10:title ?title . ?book dc10:creator ?author } UNION { ?book dc11:title ?title . ?book dc11:creator ?author } }
This query will only match a book if it has both a title and creator predicate from the same version of Dublin Core.
The SPARQL query language incorporates two styles of negation, one based on filtering results depending on whether a graph pattern does or does not match in the context of the query solution being filtered, and one based on removing solutions related to another pattern.
Filtering of query solutions is done within a FILTER
expression using NOT EXISTS
and EXISTS
.
Note that the filter scope rules
apply to the
whole group in which the filter appears.
The NOT EXISTS
filter expression tests whether a graph pattern does
not match the dataset, given the values of variables in the group graph pattern
in which the filter occurs. It does
not generate any additional bindings.
Data:
@prefix : <http://example/> . @prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> . @prefix foaf: <http://xmlns.com/foaf/0.1/> . :alice rdf:type foaf:Person . :alice foaf:name "Alice" . :bob rdf:type foaf:Person .
Query:
PREFIX rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> PREFIX foaf: <http://xmlns.com/foaf/0.1/> SELECT ?person WHERE { ?person rdf:type foaf:Person . FILTER NOT EXISTS { ?person foaf:name ?name } }
Query Result:
person |
---|
<http://example/bob> |
The filter expression EXISTS
is also provided.
It tests whether the pattern can be found in the data;
it does not generate any additional bindings.
Query:
PREFIX rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> PREFIX foaf: <http://xmlns.com/foaf/0.1/> SELECT ?person WHERE { ?person rdf:type foaf:Person . FILTER EXISTS { ?person foaf:name ?name } }
Query Result:
person |
---|
<http://example/alice> |
The other style of negation provided in SPARQL is
MINUS
which evaluates both its arguments,
then calculates solutions in the left-hand side that are not
compatible with the solutions on the right-hand side.
@prefix : <http://example/> . @prefix foaf: <http://xmlns.com/foaf/0.1/> . :alice foaf:givenName "Alice" ; foaf:familyName "Smith" . :bob foaf:givenName "Bob" ; foaf:familyName "Jones" . :carol foaf:givenName "Carol" ; foaf:familyName "Smith" .
PREFIX : <http://example/> PREFIX foaf: <http://xmlns.com/foaf/0.1/> SELECT DISTINCT ?s WHERE { ?s ?p ?o . MINUS { ?s foaf:givenName "Bob" . } }
Results:
s |
---|
<http://example/carol> |
<http://example/alice> |
NOT EXISTS
and MINUS
represent two ways of
thinking about negation, one based on
testing whether a pattern exists in the data, given the bindings
already determined by the query pattern,
and one based on removing matches based on the evaluation of
two patterns. In some cases they can produce different answers.
@prefix : <http://example/> . :a :b :c .
SELECT * { ?s ?p ?o FILTER NOT EXISTS { ?x ?y ?z } }
evaluates to a result set with no solutions because { ?x ?y ?z }
matches given any ?s ?p ?o
, so NOT EXISTS { ?x ?y ?z }
eliminates any solutions.
s | p | o |
---|
whereas with MINUS
, there is no shared variable between the
first part (?s ?p ?o
) and the second (?x ?y ?z
)
so no bindings are eliminated.
SELECT * { ?s ?p ?o MINUS { ?x ?y ?z } }
Results:
s | p | o |
---|---|---|
<http://example/a> | <http://example/b> | <http://example/c> |
Another case is where there is a concrete pattern (no variables) in the example:
PREFIX : <http://example/> SELECT * { ?s ?p ?o FILTER NOT EXISTS { :a :b :c } }
evaluates to a result set with no query solutions:
Results:s | p | o |
---|
whereas
PREFIX : <http://example/> SELECT * { ?s ?p ?o MINUS { :a :b :c } }
evaluates to result set with one query solution:
Results:
s | p | o |
---|---|---|
<http://example/a> | <http://example/b> | <http://example/c> |
because there is no match of bindings and so no solutions are eliminated.
Differences also arise because in a filter variables from the group are
in-scope. In this example, the FILTER
inside
the NOT EXISTS
has access to the value of ?n for the solution being considered.
@prefix : <http://example.com/> . :a :p 1 . :a :q 1 . :a :q 2 . :b :p 3.0 . :b :q 4.0 . :b :q 5.0 .
When using FILTER NOT EXISTS
, the test is on each possible solution to ?x :p ?n
:
PREFIX : <http://example.com/> SELECT * WHERE { ?x :p ?n FILTER NOT EXISTS { ?x :q ?m . FILTER(?n = ?m) } }
x | n |
---|---|
<http://example.com/b> | 3.0 |
whereas with MINUS
, the FILTER
inside the pattern does not have a value for ?n and it is always unbound:
PREFIX : <http://example/> SELECT * WHERE { ?x :p ?n MINUS { ?x :q ?m . FILTER(?n = ?m) } }
x | n |
---|---|
<http://example.com/b> | 3.0 |
<http://example.com/a> | 1 |
A property path is a possible route through a graph between two graph nodes. A trivial case is a property path of length exactly 1, which is a triple pattern. Property paths allow for more concise expressions for some SPARQL basic graph patterns and also add the ability to match arbitrary length paths. The ends of the path may be RDF terms or variables. Variables can not be used as part of the path itself, only the ends. Query evaluation determines all matches of a path expression and binds subject or object as appropriate.
Matching cycles in the graph is possible. A path of length zero connects a graph node to itself.
In the description below, iri is either an IRI written in full or abbreviated by a a prefixed name, or the keyword a. elt is a path element, which may itself be composed of path syntax constructs.
Syntax Form | Matches |
---|---|
iri | An IRI. A path of length one. |
^elt | Inverse path (object to subject). |
!iri or !(iri1| ...|irin) | Negated property set. An IRI which is not one of irii. !iri is short for !(iri). |
!^iri or !(iri1| ...|irij|^irij+1| ...|^irin)) | Negated property set with some inverse properties. An IRi which is not one of irii, nor one of irij+1...irin as reverse paths. !^iri is short for !(^iri). |
(elt) | A group path elt, brackets control precedence. |
elt1 / elt2 | A sequence path of elt1 followed by elt2. |
elt1 | elt2 | A alternative path of elt1 or elt2 (all possibilities are tried). |
elt* | A path of zero or more occurrences of elt. |
elt+ | A path of one or more occurrences of elt. |
elt? | A path of zero or one occurrences of elt. |
elt{n,m} | A path of between n and m occurrences of elt. |
elt{n} | A path of exactly n occurrences of elt. |
elt{n,} | A path of n or more occurrences of elt. |
elt{,n} | A path of between 0 and n occurrences of elt. |
The order of IRIs, and reverse IRIs, in a negated property set is not significant and they can occur in a mixed order.
The precedence of the syntax forms is, from highest to lowest:
Precedence is left-to-right within groups.
Alternatives: Match one or both possibilities
{ :book1 dc:title|rdfs:label ?displayString }
Sequence: Find the name of any people that Alice knows.
{ ?x foaf:mbox <mailto:alice@example> . ?x foaf:knows/foaf:name ?name . }
Sequence: Find the names of people 2 "foaf:knows" links away.
{ ?x foaf:mbox <mailto:alice@example> . ?x foaf:knows/foaf:knows/foaf:name ?name . }
This can be written as:
{ ?x foaf:mbox <mailto:alice@example> . ?x foaf:knows{2}/foaf:name ?name . }
This is the same as the SPARQL query:
{ ?x foaf:mbox <mailto:alice@example> . ?x foaf:knows [ foaf:knows [ foaf:name ?name ]]. }
or, with explicit variables:
{ ?x foaf:mbox <mailto:alice@example> . ?x foaf:knows ?a1 . ?a1 foaf:knows ?a2 . ?a2 foaf:name ?name . }
Filtering duplicates: Because someone Alice knows may well know Alice, the example above may include Alice herself. This could be avoided with:
{ ?x foaf:mbox <mailto:alice@example> . ?x foaf:knows/foaf:knows ?y . FILTER ( ?x != ?y ) ?y foaf:name ?name }
Inverse Property Paths: These two are the same query: the second is just reversing the property direction which swaps the roles of subject and object.
{ ?x foaf:mbox <mailto:alice@example> }
{ <mailto:alice@example> ^foaf:mbox ?x }
Inverse Path Sequence: Find all the people who know someone ?x knows.
{ ?x foaf:knows/^foaf:knows ?y . FILTER(?x != ?y) }
Arbitrary length match: Find the names of all the people that can be reached from Alice by foaf:knows:
{ ?x foaf:mbox <mailto:alice@example> . ?x foaf:knows+/foaf:name ?name . }
Alternatives in an arbitrary length path
?ancestor (ex:motherOf|ex:fatherOf)+ <#me>
Arbitrary length path match: Some forms of limited inference are possible as well. For example, for RDFS, all types and supertypes of a resource:
{ <http://example/thing> rdf:type/rdfs:subClassOf* ?type }
All resources and all their inferred types:
{ ?x rdf:type/rdfs:subClassOf* ?type }
Subproperty:
{ ?x ?p ?v . ?p rdfs:subPropertyOf* :property }
Negated Property Paths: Find nodes connected but not by rdf:type (either way round):
{ ?x !(rdf:type|^rdf:type) ?y }
Elements in an RDF collection:
{ :list rdf:rest*/rdf:first ?element }
Note: This path expression does not guarantee the order of the results.
SPARQL property paths treat the RDF triples as a directed, possibly cyclic, graph with named edges. Evaluation of a property path expression can lead to duplicates in the results. The property paths are equivalent to their translation into triple patterns and SPARQL UNION graph patterns, with the addition of operators for negated property paths, zero-length paths and arbitrary length paths. Any variables introduced in the equivalent pattern are not part of the results and are not already used elsewhere. They are hidden by implicit projection of the results to just the variables given in the query.
For example, on the data:
@prefix : <http://example/> . :x :p :z1 . :x :p :z2 . :z1 :q :y . :z2 :q :y .Query:
PREFIX : <http://example/> SELECT * { ?s :p/:q ?o . }
Results:
s | o |
---|---|
<http://example/x> | <http://example/y> |
<http://example/x> | <http://example/y> |
whereas if the query were written out to include the intermediate variable (?_a), no rows in the results are duplicates:
PREFIX : <http://example/> SELECT * { ?s :p ?_a . ?_a :q ?o . }
Results:
s | a | o |
---|---|---|
<http://example/x> | <http://example/z1> | <http://example/y> |
<http://example/x> | <http://example/z2> | <http://example/y> |
Where the query matches on arbitrary length paths, each cycle is considered
at most once by stopping if an RDF term in the data would be matched again
in the evaluation of the +
or *
property path operators.
For example, on the data, which is a graph with a cycle in it,
@prefix : <http://example/> . :x :p :y . :y :p :x .
and the query:
PREFIX : <http://example/> SELECT * { :x :p+ ?o }
the results are:
o |
---|
<http://example/y> |
<http://example/x> |
because :p+
is a property path expression that is "one or more
:p
properties". The two answers correspond to matching once for
:x :p :y
then once for the case of :x :p :y . :y :p :x
.
Using :p*
instead of :p+
leads to a duplicate for
:x
because it is possible to match in two different ways in finding paths starting at :x
; once with :p{0}
PREFIX : <http://example/> SELECT * { :x :p* ?o }
giving results of:
o |
---|
<http://example/x> |
<http://example/y> |
<http://example/x> |
The order of results in these examples is not significant.
The value of an expression can be added to a solution mapping by binding a new variable to the value of the expression, which is an RDF term. In SPARQL, this binding within a query solution is never changed and this is checked by the variable scoping rules. The new variable must not already be in-scope in the query at the point where it is used. The variable can then be used in the query and also can be returned in results.
Three syntax forms allow this: the BIND
keyword,
expressions in the
SELECT
clause and expressions in the GROUP BY
clause.
The assignment form is (expression AS ?var)
.
If the evaluation of the expression produces an error, the variable remains unbound for that solution.
Data can also be directly included in a query using
a BINDINGS
clause.
The BIND
form allows a value to be assigned to a variable in a
group graph pattern. Use of BIND
is a separate element of a group graph pattern and it ends
any basic graph pattern.
Example:
Data:
@prefix dc: <http://purl.org/dc/elements/1.1/> . @prefix : <http://example.org/book/> . @prefix ns: <http://example.org/ns#> . :book1 dc:title "SPARQL Tutorial" . :book1 ns:price 42 . :book1 ns:discount 0.2 . :book2 dc:title "The Semantic Web" . :book2 ns:price 23 . :book2 ns:discount 0.25 .
Query:
PREFIX dc: <http://purl.org/dc/elements/1.1/> PREFIX ns: <http://example.org/ns#> SELECT ?title ?price { ?x ns:price ?p . ?x ns:discount ?discount BIND (?p*(1-?discount) AS ?price) FILTER(?price < 20) ?x dc:title ?title . }
Equivalent query (BIND
ends the basic graph pattern;
the FILTER
applies to the whole group graph pattern):
PREFIX dc: <http://purl.org/dc/elements/1.1/> PREFIX ns: <http://example.org/ns#> SELECT ?title ?price { { ?x ns:price ?p . ?x ns:discount ?discount BIND (?p*(1-?discount) AS ?price) } {?x dc:title ?title . } FILTER(?price < 20) }
Results:
title | price |
---|---|
"The Semantic Web" | 17.25 |
A BINDINGS
clause in a query provides an unordered
solution sequence
which is combined with the results of query evaluation by a join
operation. It can be used by an application to provide specific requirements on query results
and also by SPARQL query engine implementations that provide
federated query
through the SERVICE
keyword to send a more constrained query to a
remote query service.
Data:
@prefix dc: <http://purl.org/dc/elements/1.1/> . @prefix : <http://example.org/book/> . @prefix ns: <http://example.org/ns#> . :book1 dc:title "SPARQL Tutorial" . :book1 ns:price 42 . :book2 dc:title "The Semantic Web" . :book2 ns:price 23 .
Query:
PREFIX dc: <http://purl.org/dc/elements/1.1/> PREFIX : <http://example.org/book/> PREFIX ns: <http://example.org/ns#> SELECT ?book ?title ?price { ?book dc:title ?title ; ns:price ?price . } BINDINGS ?book { (:book1) }
Result:
If a variable has no value for a particular query solution in the
BINDINGS
clause, the keyword UNDEF
is used
instead of an RDF term.
PREFIX dc: <http://purl.org/dc/elements/1.1/> PREFIX : <http://example.org/book/> PREFIX ns: <http://example.org/ns#> SELECT ?book ?title ?price { ?book dc:title ?title ; ns:price ?price . } BINDINGS ?book ?title { (UNDEF "SPARQL Tutorial") (:book2 UNDEF) }
Aggregates apply expressions over groups of solutions. By default a solution set consists of a single group, containing all solutions.
Grouping may be specified using the GROUP BY
syntax.
Aggregates defined in version 1.1 of SPARQL are
COUNT
, SUM
, MIN
, MAX
, AVG
, GROUP_CONCAT
, and SAMPLE
.
Aggregates are used where the querier wishes to see a result which is computed over a group of solutions, rather than a single solution. For example the maximum value that a particular variable takes, rather than each value individually.
Data:
@prefix : <http://books.example/> . :org1 :affiliates :auth1, :auth2 . :auth1 :writesBook :book1, :book2 . :book1 :price 9 . :book2 :price 5 . :auth2 :writesBook :book3 . :book3 :price 7 . :org2 :affiliates :auth3 . :auth3 :writesBook :book4 . :book4 :price 7 .
Query:
PREFIX : <http://books.example/> SELECT (SUM(?lprice) AS ?totalPrice) WHERE { ?org :affiliates ?auth . ?auth :writesBook ?book . ?book :price ?lprice . } GROUP BY ?org HAVING (SUM(?lprice) > 10)
Results:
totalPrice |
---|
21 |
This example demonstrates two features of aggregates: GROUP BY
, which
groups query solutions according to one or more expressions (in this case
?org
), and HAVING
, which is analogous to a FILTER
expression, but operates over groups, rather than individual solutions.
The example is produced by grouping solutions according to the GROUP BY
expression (i.e. all solutions where ?org
takes a particular value appear
within the same group), and evaluating the Set Function SUM
over that group.
The groups are then filtered by the HAVING
expression, which removes
all groups where SUM(?lprice)
is not greater than 10.
In aggregate queries and sub-queries, variables that appear in the
query pattern, but are not in the GROUP BY
clause, can only be
projected or used in select expressions if they are aggregated. The
SAMPLE
aggregate may be used for this purpose. For details see the
section on Projection Restrictions.
It should be noted that as per functions, aggregate expressions are required to be aliased (again, similar to the BIND
clause, using the keyword AS
) in order to project them from queries or subqueries. In the example above this is done using the variable ?totalPrice
. It is an error for aggregates to project variables with a name already used in other aggregate projections, or in the WHERE
clause.
In order to calculate aggregate values for a solution, the solution is first divided into one or more groups, and the aggregate value is calculated for each group.
If aggregates are used in the query level in SELECT
,
HAVING
or ORDER BY
but the GROUP BY
term is not used,
then this is taken to be a single implicit group, to which all solutions belong.
Within GROUP BY
clauses the binding keyword, AS
, may be used, such as GROUP BY (?x + ?y AS ?z)
. This is equivalent to { ... BIND (?x + ?y AS ?z) } GROUP BY ?z
.
For example, given a solution sequence S, ( {?x→2, ?y→3}, {?x→2, ?y→5}, {?x→6, ?y→7} ), we might wish to group the solutions according to the value of ?x, and calculate the average of the values of ?y for each group.
This could be written as:
SELECT (AVG(?y) AS ?avg) WHERE { ?a :x ?x ; :y ?y . } GROUP BY ?x
HAVING
operates over grouped solution sets, in the same way that FILTER
operates over un-grouped ones.
HAVING
expressions have the same evaluation rules as projections from
grouped queries, as described in the following section.
An example of the use of HAVING
is given below.
PREFIX : <http://data.example/> SELECT (AVG(?size) AS ?asize) WHERE { ?x :size ?size } GROUP BY ?x HAVING(AVG(?size) > 10)
This will return average sizes, grouped by the subject, but only where the mean size is greater than 10.
In a query level which uses aggregates, only expressions consisting of aggregates and constants may be projected, with one exception. When GROUP BY
is given with one or more simple expressions consisting of just a variable, those variables may be projected from the level.
For example, the following query is legal as ?x is given as a GROUP BY
term.
PREFIX : <http://example.com/data/#> SELECT ?x (MIN(?y) * 2 AS ?min) WHERE { ?x :p ?y . ?x :q ?z . } GROUP BY ?x (STR(?z))
Note that it would not be legal to project STR(?z)
as this is not a simple variable expression. However, with GROUP BY (STR(?z) AS ?strZ)
it would be possible to project ?strZ
.
Other expressions, not using GROUP BY
variables, or aggregates may have non-deterministic values projected from their groups using the SAMPLE
aggregate.
This section shows an example query using aggregation, which demonstrates how errors are handled in results, in the presence of aggregates.
Data:
@prefix : <http://example.com/data/#> . :x :p 1, 2, 3, 4 . :y :p 1, _:b2, 3, 4 . :z :p 1.0, 2.0, 3.0, 4 .
Query:
PREFIX : <http://example.com/data/#> SELECT ?g (AVG(?p) AS ?avg) ((MIN(?p) + MAX(?p)) / 2 AS ?c) WHERE { ?g :p ?p . } GROUP BY ?g
Result:
g | avg | c |
---|---|---|
<http://example.com/data/#x> | 2.5 | 2.5 |
<http://example.com/data/#y> | ||
<http://example.com/data/#z> | 2.5 | 2.5 |
Note that the bindings for the :y group is not included in the results as the evaluation of Avg({1, _:b2, 3, 4}), and (_:b2 + 4) / 2 is an error, removing the bindings from the solution.
Subqueries are a way to embed SPARQL queries within other queries, normally to achieve results which cannot otherwise be achieved, such as limiting the number of results from some sub-expression within the query.
Due to the bottom-up nature of SPARQL query evaluation, the subqueries are evaluated logically first, and the results are projected up to the outer query.
Note that only variables projected out of the subquery will be visible, or in scope to the outer query.
Data:
@prefix : <http://people.example/> . :alice :name "Alice", "Alice Foo", "A. Foo" . :alice :knows :bob, :carol . :bob :name "Bob", "Bob Bar", "B. Bar" . :carol :name "Carol", "Carol Baz", "C. Baz" .
Return a name (the one with the lowest sort order) for all the people that know Alice and have a name.
Query:
PREFIX : <http://people.example/> PREFIX : <http://people.example/> SELECT ?y ?minName WHERE { :alice :knows ?y . { SELECT ?y (MIN(?name) AS ?minName) WHERE { ?y :name ?name . } GROUP BY ?y } }
Results:
y | minName |
---|---|
:bob | "B. Bar" |
:carol | "C. Baz" |
This result is achieved by first evaluating the inner query:
SELECT ?y (MIN(?name) AS ?minName) WHERE { ?y :name ?name . } GROUP BY ?y
This produces the following solution sequence:
y | minName |
---|---|
:alice | "A. Foo" |
:bob | "B. Bar" |
:carol | "C. Baz" |
Which is joined with the results of the outer query:
y |
---|
:bob |
:carol |
The RDF data model expresses information as graphs consisting of triples with subject, predicate and object. Many RDF data stores hold multiple RDF graphs and record information about each graph, allowing an application to make queries that involve information from more than one graph.
A SPARQL query is executed against an RDF Dataset which represents a collection of graphs. An RDF Dataset comprises one graph, the default graph, which does not have a name, and zero or more named graphs, where each named graph is identified by an IRI. A SPARQL query can match different parts of the query pattern against different graphs as described in section 13.3 Querying the Dataset.
An RDF Dataset may contain zero named graphs; an RDF Dataset always contains one default graph. A query does not need to involve matching the default graph; the query can just involve matching named graphs.
The graph that is used for matching a basic graph pattern is the active
graph. In the previous sections, all queries have been shown executed
against a single graph, the default graph of an RDF dataset as the active graph.
The GRAPH
keyword is used to make the active graph one of all of
the named graphs in the dataset for part of the query.
The definition of RDF Dataset does not restrict the relationships of named and default graphs. Information can be repeated in different graphs; relationships between graphs can be exposed. Two useful arrangements are:
# Default graph @prefix dc: <http://purl.org/dc/elements/1.1/> . <http://example.org/bob> dc:publisher "Bob" . <http://example.org/alice> dc:publisher "Alice" .
# Named graph: http://example.org/bob @prefix foaf: <http://xmlns.com/foaf/0.1/> . _:a foaf:name "Bob" . _:a foaf:mbox <mailto:bob@oldcorp.example.org> .
# Named graph: http://example.org/alice @prefix foaf: <http://xmlns.com/foaf/0.1/> . _:a foaf:name "Alice" . _:a foaf:mbox <mailto:alice@work.example.org> .
In this example, the default graph contains the names of the publishers of two named graphs. The triples in the named graphs are not visible in the default graph in this example.
Example 2:
RDF data can be combined by the RDF merge [RDF-MT] of graphs. One possible arrangement of graphs in an RDF Dataset is to have the default graph be the RDF merge of some or all of the information in the named graphs.
In this next example, the named graphs contain the same triples as before. The RDF dataset includes an RDF merge of the named graphs in the default graph, re-labeling blank nodes to keep them distinct.
# Default graph @prefix foaf: <http://xmlns.com/foaf/0.1/> . _:x foaf:name "Bob" . _:x foaf:mbox <mailto:bob@oldcorp.example.org> . _:y foaf:name "Alice" . _:y foaf:mbox <mailto:alice@work.example.org> .
# Named graph: http://example.org/bob @prefix foaf: <http://xmlns.com/foaf/0.1/> . _:a foaf:name "Bob" . _:a foaf:mbox <mailto:bob@oldcorp.example.org> .
# Named graph: http://example.org/alice @prefix foaf: <http://xmlns.com/foaf/0.1/> . _:a foaf:name "Alice" . _:a foaf:mbox <mailto:alice@work.example> .
In an RDF merge, blank nodes in the merged graph are not shared with blank nodes from the graphs being merged.
A SPARQL query may specify the dataset to be used for matching by using the
FROM
clause and the FROM NAMED
clause to describe the
RDF dataset. If a query provides such a dataset description, then it is used in
place of any dataset that the query service would use if no dataset description
is provided in a query. The RDF dataset may also be
specified in a SPARQL protocol request, in which case the protocol description
overrides any description in the query itself. A query service may refuse a query
request if the dataset description is not acceptable to the service.
The FROM
and FROM NAMED
keywords allow a query to specify
an RDF dataset by reference; they indicate that the dataset should include graphs
that are obtained from representations of the resources identified by the given
IRIs (i.e. the absolute form of the given IRI references). The dataset resulting
from a number of FROM
and FROM NAMED
clauses is:
FROM
clauses, andFROM NAMED
clause.If there is no FROM
clause, but there is one or more FROM NAMED
clauses, then the dataset includes an empty graph for the default graph.
Each FROM
clause contains an IRI that indicates a graph to be
used to form the default graph. This does not put the graph in as a named graph.
In this example, the RDF Dataset contains a single default graph and no named graphs:
# Default graph (located at http://example.org/foaf/aliceFoaf) @prefix foaf: <http://xmlns.com/foaf/0.1/> . _:a foaf:name "Alice" . _:a foaf:mbox <mailto:alice@work.example> .
If a query provides more than one FROM
clause, providing more than
one IRI to indicate the default graph, then the default graph is the
RDF merge of the
graphs obtained from representations of the resources identified by the given IRIs.
A query can supply IRIs for the named graphs in the RDF Dataset using the
FROM NAMED
clause. Each IRI is used to provide one named graph in the
RDF Dataset. Using the same IRI in two or more FROM NAMED
clauses results
in one named graph with that IRI appearing in the dataset.
# Graph: http://example.org/bob @prefix foaf: <http://xmlns.com/foaf/0.1/> . _:a foaf:name "Bob" . _:a foaf:mbox <mailto:bob@oldcorp.example.org> .
# Graph: http://example.org/alice @prefix foaf: <http://xmlns.com/foaf/0.1/> . _:a foaf:name "Alice" . _:a foaf:mbox <mailto:alice@work.example> .
... FROM NAMED <http://example.org/alice> FROM NAMED <http://example.org/bob> ...
The FROM NAMED
syntax suggests that the IRI identifies the corresponding
graph, but the relationship between an IRI and a graph in an RDF dataset
is indirect. The IRI identifies a resource, and the resource is represented by a
graph (or, more precisely: by a document that serializes a graph). For
further details
see [WEBARCH].
The FROM
clause and FROM NAMED
clause can be used in
the same query.
# Default graph (located at http://example.org/dft.ttl) @prefix dc: <http://purl.org/dc/elements/1.1/> . <http://example.org/bob> dc:publisher "Bob Hacker" . <http://example.org/alice> dc:publisher "Alice Hacker" .
# Named graph: http://example.org/bob @prefix foaf: <http://xmlns.com/foaf/0.1/> . _:a foaf:name "Bob" . _:a foaf:mbox <mailto:bob@oldcorp.example.org> .
# Named graph: http://example.org/alice @prefix foaf: <http://xmlns.com/foaf/0.1/> . _:a foaf:name "Alice" . _:a foaf:mbox <mailto:alice@work.example.org> .
PREFIX foaf: <http://xmlns.com/foaf/0.1/> PREFIX dc: <http://purl.org/dc/elements/1.1/> SELECT ?who ?g ?mbox FROM <http://example.org/dft.ttl> FROM NAMED <http://example.org/alice> FROM NAMED <http://example.org/bob> WHERE { ?g dc:publisher ?who . GRAPH ?g { ?x foaf:mbox ?mbox } }
The RDF Dataset for this query contains a default graph and two named graphs.
The GRAPH
keyword is described below.
The actions required to construct the dataset are not determined by the
dataset description alone. If an IRI is given twice in a dataset
description, either by using two FROM
clauses, or a FROM
clause and a
FROM NAMED
clause, then it does not assume that exactly one or exactly
two attempts are made to obtain an RDF graph associated with the IRI.
Therefore, no assumptions can be made about blank node identity in
triples obtained from the two occurrences in the dataset description.
In general, no assumptions can be made about the equivalence of the graphs.
When querying a collection of graphs, the GRAPH
keyword is used
to match patterns against named graphs. GRAPH
can provide an IRI to select
one graph or use a variable which will range over the IRI of all the named graphs in the query's RDF dataset.
The use of GRAPH
changes the active graph for matching
graph patterns within that part of the query. Outside the use of GRAPH
,
matching is done using the default graph.
The following two graphs will be used in examples:
# Named graph: http://example.org/foaf/aliceFoaf @prefix foaf: <http://xmlns.com/foaf/0.1/> . @prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> . @prefix rdfs: <http://www.w3.org/2000/01/rdf-schema#> . _:a foaf:name "Alice" . _:a foaf:mbox <mailto:alice@work.example> . _:a foaf:knows _:b . _:b foaf:name "Bob" . _:b foaf:mbox <mailto:bob@work.example> . _:b foaf:nick "Bobby" . _:b rdfs:seeAlso <http://example.org/foaf/bobFoaf> . <http://example.org/foaf/bobFoaf> rdf:type foaf:PersonalProfileDocument .
# Named graph: http://example.org/foaf/bobFoaf @prefix foaf: <http://xmlns.com/foaf/0.1/> . @prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> . @prefix rdfs: <http://www.w3.org/2000/01/rdf-schema#> . _:z foaf:mbox <mailto:bob@work.example> . _:z rdfs:seeAlso <http://example.org/foaf/bobFoaf> . _:z foaf:nick "Robert" . <http://example.org/foaf/bobFoaf> rdf:type foaf:PersonalProfileDocument .
The query below matches the graph pattern against each of the named graphs in the
dataset and forms solutions which have the src
variable bound to
IRIs of the graph being matched. The graph pattern is matched with the active
graph being each of the named graphs in the dataset.
PREFIX foaf: <http://xmlns.com/foaf/0.1/> SELECT ?src ?bobNick FROM NAMED <http://example.org/foaf/aliceFoaf> FROM NAMED <http://example.org/foaf/bobFoaf> WHERE { GRAPH ?src { ?x foaf:mbox <mailto:bob@work.example> . ?x foaf:nick ?bobNick } }
The query result gives the name of the graphs where the information was found and the value for Bob's nick:
The query can restrict the matching applied to a specific graph by supplying
the graph IRI. This sets the active graph to the graph named by the IRI. This query looks for Bob's nick as given in the graph http://example.org/foaf/bobFoaf
.
PREFIX foaf: <http://xmlns.com/foaf/0.1/> PREFIX data: <http://example.org/foaf/> SELECT ?nick FROM NAMED <http://example.org/foaf/aliceFoaf> FROM NAMED <http://example.org/foaf/bobFoaf> WHERE { GRAPH data:bobFoaf { ?x foaf:mbox <mailto:bob@work.example> . ?x foaf:nick ?nick } }
which yields a single solution:
A variable used in the GRAPH
clause may also be used in another
GRAPH
clause or in a graph pattern matched against the default graph
in the dataset.
The query below uses the graph
with IRI http://example.org/foaf/aliceFoaf
to find the profile document
for Bob; it then matches another pattern against that graph. The pattern in the
second GRAPH
clause finds the blank node (variable w
)
for the person with the same mail box (given by variable mbox
) as
found in the first GRAPH
clause (variable whom
), because
the blank node used to match for variable whom
from Alice's FOAF
file is not the same as the blank node in the profile document (they are in different
graphs).
PREFIX data: <http://example.org/foaf/> PREFIX foaf: <http://xmlns.com/foaf/0.1/> PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#> SELECT ?mbox ?nick ?ppd FROM NAMED <http://example.org/foaf/aliceFoaf> FROM NAMED <http://example.org/foaf/bobFoaf> WHERE { GRAPH data:aliceFoaf { ?alice foaf:mbox <mailto:alice@work.example> ; foaf:knows ?whom . ?whom foaf:mbox ?mbox ; rdfs:seeAlso ?ppd . ?ppd a foaf:PersonalProfileDocument . } . GRAPH ?ppd { ?w foaf:mbox ?mbox ; foaf:nick ?nick } }
Any triple in Alice's FOAF file giving Bob's nick
is not used to
provide a nick for Bob because the pattern involving variable nick
is restricted by ppd
to a particular Personal Profile Document.
Query patterns can involve both the default graph and the named graphs. In this example, an aggregator has read in a Web resource on two different occasions. Each time a graph is read into the aggregator, it is given an IRI by the local system. The graphs are nearly the same but the email address for "Bob" has changed.
In this example, the default graph is being used to record the provenance information and the RDF data actually read is kept in two separate graphs, each of which is given a different IRI by the system. The RDF dataset consists of two named graphs and the information about them.
RDF Dataset:
# Default graph @prefix dc: <http://purl.org/dc/elements/1.1/> . @prefix g: <tag:example.org,2005-06-06:> . @prefix xsd: <http://www.w3.org/2001/XMLSchema#> . g:graph1 dc:publisher "Bob" . g:graph1 dc:date "2004-12-06"^^xsd:date . g:graph2 dc:publisher "Bob" . g:graph2 dc:date "2005-01-10"^^xsd:date .
# Graph: locally allocated IRI: tag:example.org,2005-06-06:graph1 @prefix foaf: <http://xmlns.com/foaf/0.1/> . _:a foaf:name "Alice" . _:a foaf:mbox <mailto:alice@work.example> . _:b foaf:name "Bob" . _:b foaf:mbox <mailto:bob@oldcorp.example.org> .
# Graph: locally allocated IRI: tag:example.org,2005-06-06:graph2 @prefix foaf: <http://xmlns.com/foaf/0.1/> . _:a foaf:name "Alice" . _:a foaf:mbox <mailto:alice@work.example> . _:b foaf:name "Bob" . _:b foaf:mbox <mailto:bob@newcorp.example.org> .
This query finds email addresses, detailing the name of the person and the date the information was discovered.
PREFIX foaf: <http://xmlns.com/foaf/0.1/> PREFIX dc: <http://purl.org/dc/elements/1.1/> SELECT ?name ?mbox ?date WHERE { ?g dc:publisher ?name ; dc:date ?date . GRAPH ?g { ?person foaf:name ?name ; foaf:mbox ?mbox } }
The results show that the email address for "Bob" has changed.
This document incorporates the syntax for SPARQL Federated Query.
This feature is defined in the document SPARQL 1.1 Federated Query.
Query patterns generate an unordered collection of solutions, each solution being a partial function from variables to RDF terms. These solutions are then treated as a sequence (a solution sequence), initially in no specific order; any sequence modifiers are then applied to create another sequence. Finally, this latter sequence is used to generate one of the results of a SPARQL query form.
A solution sequence modifier is one of:
Modifiers are applied in the order given by the list above.
The ORDER BY
clause establishes the order of a solution sequence.
Following the ORDER BY
clause is a sequence of order comparators, composed of an expression and an optional order modifier (either ASC()
or DESC()
). Each ordering comparator is either ascending (indicated by the ASC()
modifier or by no modifier) or descending (indicated by the DESC()
modifier).
PREFIX foaf: <http://xmlns.com/foaf/0.1/> SELECT ?name WHERE { ?x foaf:name ?name } ORDER BY ?name
PREFIX : <http://example.org/ns#> PREFIX foaf: <http://xmlns.com/foaf/0.1/> SELECT ?name WHERE { ?x foaf:name ?name ; :empId ?emp } ORDER BY DESC(?emp)
PREFIX : <http://example.org/ns#> PREFIX foaf: <http://xmlns.com/foaf/0.1/> SELECT ?name WHERE { ?x foaf:name ?name ; :empId ?emp } ORDER BY ?name DESC(?emp)
The "<" operator (see the Operator Mapping and 17.3.1 Operator Extensibility) defines
the relative order of pairs of numerics
, simple literals
, xsd:strings
, xsd:booleans
and xsd:dateTimes
. Pairs of IRIs are ordered by comparing them as simple literals
.
SPARQL also fixes an order between some kinds of RDF terms that would not otherwise be ordered:
A plain literal is lower than an RDF literal with type xsd:string
of the same lexical form.
SPARQL does not define a total ordering of all possible RDF terms. Here are a few examples of pairs of terms for which the relative order is undefined:
This list of variable bindings is in ascending order:
RDF Term | Reason |
---|---|
Unbound results sort earliest. | |
_:z | Blank nodes follow unbound. |
_:a | There is no relative ordering of blank nodes. |
<http://script.example/Latin> | IRIs follow blank nodes. |
<http://script.example/Кириллица> | The character in the 23rd position, "К", has a unicode codepoint 0x41A, which is higher than 0x4C ("L"). |
<http://script.example/漢字> | The character in the 23rd position, "漢", has a unicode codepoint 0x6F22, which is higher than 0x41A ("К"). |
"http://script.example/Latin" | Simple literals follow IRIs. |
"http://script.example/Latin"^^xsd:string | xsd:strings follow simple literals. |
The ascending order of two solutions with respect to an ordering comparator is established by substituting the solution bindings into the expressions and comparing them with the "<" operator. The descending order is the reverse of the ascending order.
The relative order of two solutions is the relative order of the two solutions with respect to the first ordering comparator in the sequence. For solutions where the substitutions of the solution bindings produce the same RDF term, the order is the relative order of the two solutions with respect to the next ordering comparator. The relative order of two solutions is undefined if no order expression evaluated for the two solutions produces distinct RDF terms.
Ordering a sequence of solutions always results in a sequence with the same number of solutions in it.
Using ORDER BY
on a solution sequence for a CONSTRUCT
or
DESCRIBE
query has no direct effect because only SELECT
returns
a sequence of results. Used in combination with LIMIT
and OFFSET
,
ORDER BY
can be used to return results generated from a different slice of the solution sequence.
An ASK
query does not include ORDER BY
, LIMIT
or OFFSET
.
The solution sequence can be transformed into one involving only a subset of the variables. For each solution in the sequence, a new solution is formed using a specified selection of the variables using the SELECT query form.
The following example shows a query to extract just the names of people described in an RDF graph using FOAF properties.
@prefix foaf: <http://xmlns.com/foaf/0.1/> . _:a foaf:name "Alice" . _:a foaf:mbox <mailto:alice@work.example> . _:b foaf:name "Bob" . _:b foaf:mbox <mailto:bob@work.example> .
PREFIX foaf: <http://xmlns.com/foaf/0.1/> SELECT ?name WHERE { ?x foaf:name ?name }
name |
---|
"Bob" |
"Alice" |
A solution sequence with no DISTINCT
or REDUCED
query modifier
will preserve duplicate solutions.
Data:
@prefix foaf: <http://xmlns.com/foaf/0.1/> . _:x foaf:name "Alice" . _:x foaf:mbox <mailto:alice@example.com> . _:y foaf:name "Alice" . _:y foaf:mbox <mailto:asmith@example.com> . _:z foaf:name "Alice" . _:z foaf:mbox <mailto:alice.smith@example.com> .
Query:
PREFIX foaf: <http://xmlns.com/foaf/0.1/> SELECT ?name WHERE { ?x foaf:name ?name }
Results:
name |
---|
"Alice" |
"Alice" |
"Alice" |
The modifiers DISTINCT
and REDUCED
affect whether duplicates are included in the query results.
The DISTINCT
solution modifier eliminates duplicate solutions.
Only one solution solution that binds the same variables to the same RDF terms is returned from the query.
PREFIX foaf: <http://xmlns.com/foaf/0.1/> SELECT DISTINCT ?name WHERE { ?x foaf:name ?name }
name |
---|
"Alice" |
Note that, per the order of solution sequence modifiers, duplicates are eliminated before either limit or offset is applied.
While the DISTINCT
modifier ensures that duplicate solutions are eliminated from the solution set, REDUCED
simply permits them to be eliminated. The cardinality of any set of variable bindings in a REDUCED
solution set is at least one and not more than the cardinality of the solution set with no DISTINCT
or REDUCED
modifier. For example, using the data above, the query
PREFIX foaf: <http://xmlns.com/foaf/0.1/> SELECT REDUCED ?name WHERE { ?x foaf:name ?name }
may have one, two (shown here) or three solutions:
name |
---|
"Alice" |
"Alice" |
OFFSET
causes the solutions generated to start after the specified
number of solutions. An OFFSET
of zero has no effect.
Using
LIMIT
and OFFSET
to select different subsets of the query solutions
will not be useful unless the order is made predictable by using ORDER BY
.
PREFIX foaf: <http://xmlns.com/foaf/0.1/> SELECT ?name WHERE { ?x foaf:name ?name } ORDER BY ?name LIMIT 5 OFFSET 10
The LIMIT
clause puts an upper bound on the number of solutions returned. If the
number of actual solutions, after OFFSET
is applied, is greater than the limit,
then at most the limit number of solutions will be returned.
PREFIX foaf: <http://xmlns.com/foaf/0.1/> SELECT ?name WHERE { ?x foaf:name ?name } LIMIT 20
A LIMIT
of 0 would cause no results to be returned. A limit may not be negative.
SPARQL has four query forms. These query forms use the solutions from pattern matching to form result sets or RDF graphs. The query forms are:
- SELECT
- Returns all, or a subset of, the variables bound in a query pattern match.
- CONSTRUCT
- Returns an RDF graph constructed by substituting variables in a set of triple templates.
- ASK
- Returns a boolean indicating whether a query pattern matches or not.
- DESCRIBE
- Returns an RDF graph that describes the resources found.
Formats such as
SPARQL 1.1 Query Results JSON Format,
SPARQL Query Results XML Format or
SPARQL 1.1 Query Results CSV and TSV Formats
can be used to serialize the result set from a
SELECT
query or the boolean result of an ASK
query.
The SELECT form of results returns variables and their bindings directly. It combines the operations of projecting the required variables with introducing new variable bindings into a query solution.
Specific variables and their bindings are
returned when a list of variable names is given in the SELECT clause. The syntax
SELECT *
is an abbreviation that
selects all of the variables that are in-scope
at that point in the query. It excludes variables only used in
FILTER
, in the right-hand side of MINUS
,
and takes account of subqueries.
Use of SELECT *
is only permitted when the
query does not have a GROUP BY
clause.
@prefix foaf: <http://xmlns.com/foaf/0.1/> . _:a foaf:name "Alice" . _:a foaf:knows _:b . _:a foaf:knows _:c . _:b foaf:name "Bob" . _:c foaf:name "Clare" . _:c foaf:nick "CT" .
PREFIX foaf: <http://xmlns.com/foaf/0.1/> SELECT ?nameX ?nameY ?nickY WHERE { ?x foaf:knows ?y ; foaf:name ?nameX . ?y foaf:name ?nameY . OPTIONAL { ?y foaf:nick ?nickY } }
Result sets can be accessed by a local API but also can be serialized into either JSON, XML, CSV or TSV.
SPARQL 1.1 Query Results JSON Format:
{ "head": { "vars": [ "nameX" , "nameY" , "nickY" ] } , "results": { "bindings": [ { "nameX": { "type": "literal" , "value": "Alice" } , "nameY": { "type": "literal" , "value": "Bob" } } , { "nameX": { "type": "literal" , "value": "Alice" } , "nameY": { "type": "literal" , "value": "Clare" } , "nickY": { "type": "literal" , "value": "CT" } } ] } }
SPARQL Query Results XML Format:
<?xml version="1.0"?> <sparql xmlns="http://www.w3.org/2005/sparql-results#"> <head> <variable name="nameX"/> <variable name="nameY"/> <variable name="nickY"/> </head> <results> <result> <binding name="nameX"> <literal>Alice</literal> </binding> <binding name="nameY"> <literal>Bob</literal> </binding> </result> <result> <binding name="nameX"> <literal>Alice</literal> </binding> <binding name="nameY"> <literal>Clare</literal> </binding> <binding name="nickY"> <literal>CT</literal> </binding> </result> </results> </sparql>
As well as choosing which variables from the pattern matching are included in the results, the SELECT clause can also introduce new variables. The rules of assignment in SELECT expression are the same as for assignment in BIND. The expression combines variable bindings already in the query solution, or defined earlier in the SELECT clause, to produce a binding in the query solution.
The scoping for (expr AS v)
applies immediately. In
SELECT
expressions, the variable may be used in an expression
later in the same SELECT
clause and may not be
be assigned again in the same SELECT
clause.
Example:
Data:
@prefix dc: <http://purl.org/dc/elements/1.1/> . @prefix : <http://example.org/book/> . @prefix ns: <http://example.org/ns#> . :book1 dc:title "SPARQL Tutorial" . :book1 ns:price 42 . :book1 ns:discount 0.2 . :book2 dc:title "The Semantic Web" . :book2 ns:price 23 . :book2 ns:discount 0.25 .
Query:
PREFIX dc: <http://purl.org/dc/elements/1.1/> PREFIX ns: <http://example.org/ns#> SELECT ?title (?p*(1-?discount) AS ?price) { ?x ns:price ?p . ?x dc:title ?title . ?x ns:discount ?discount }
Results:
title | price |
---|---|
"The Semantic Web" | 17.25 |
"SPARQL Tutorial" | 33.6 |
New variables can also be used in expressions if they are introduced earlier, syntactically, in the same SELECT clause:
PREFIX dc: <http://purl.org/dc/elements/1.1/> PREFIX ns: <http://example.org/ns#> SELECT ?title (?p AS ?fullPrice) (?fullPrice*(1-?discount) AS ?customerPrice) { ?x ns:price ?p . ?x dc:title ?title . ?x ns:discount ?discount }
Results:
title | fullPrice | customerPrice |
---|---|---|
"The Semantic Web" | 23 | 17.25 |
"SPARQL Tutorial" | 42 | 33.6 |
The CONSTRUCT
query form returns a single RDF graph specified by
a graph template. The result is an RDF graph formed by taking each query solution
in the solution sequence, substituting for the variables in the graph template,
and combining the triples into a single RDF graph by set union.
If any such instantiation produces a triple containing an unbound variable or an illegal RDF construct, such as a literal in subject or predicate position, then that triple is not included in the output RDF graph. The graph template can contain triples with no variables (known as ground or explicit triples), and these also appear in the output RDF graph returned by the CONSTRUCT query form.
@prefix foaf: <http://xmlns.com/foaf/0.1/> . _:a foaf:name "Alice" . _:a foaf:mbox <mailto:alice@example.org> .
PREFIX foaf: <http://xmlns.com/foaf/0.1/> PREFIX vcard: <http://www.w3.org/2001/vcard-rdf/3.0#> CONSTRUCT { <http://example.org/person#Alice> vcard:FN ?name } WHERE { ?x foaf:name ?name }
creates vcard properties from the FOAF information:
@prefix vcard: <http://www.w3.org/2001/vcard-rdf/3.0#> . <http://example.org/person#Alice> vcard:FN "Alice" .
A template can create an RDF graph containing blank nodes. The blank node labels are scoped to the template for each solution. If the same label occurs twice in a template, then there will be one blank node created for each query solution, but there will be different blank nodes for triples generated by different query solutions.
@prefix foaf: <http://xmlns.com/foaf/0.1/> . _:a foaf:givenname "Alice" . _:a foaf:family_name "Hacker" . _:b foaf:firstname "Bob" . _:b foaf:surname "Hacker" .
PREFIX foaf: <http://xmlns.com/foaf/0.1/> PREFIX vcard: <http://www.w3.org/2001/vcard-rdf/3.0#> CONSTRUCT { ?x vcard:N _:v . _:v vcard:givenName ?gname . _:v vcard:familyName ?fname } WHERE { { ?x foaf:firstname ?gname } UNION { ?x foaf:givenname ?gname } . { ?x foaf:surname ?fname } UNION { ?x foaf:family_name ?fname } . }
creates vcard properties corresponding to the FOAF information:
@prefix vcard: <http://www.w3.org/2001/vcard-rdf/3.0#> . _:v1 vcard:N _:x . _:x vcard:givenName "Alice" . _:x vcard:familyName "Hacker" . _:v2 vcard:N _:z . _:z vcard:givenName "Bob" . _:z vcard:familyName "Hacker" .
The use of variable x
in the template, which in this example will be bound to
blank nodes with labels _:a
and _:b
in the data,
causes different blank node labels (_:v1
and _:v2
) in the resulting RDF graph.
Using CONSTRUCT
, it is possible to extract parts or the whole of
graphs from the target RDF dataset. This first example returns the graph (if it
is in the dataset) with IRI label http://example.org/aGraph
; otherwise,
it returns an empty graph.
CONSTRUCT { ?s ?p ?o } WHERE { GRAPH <http://example.org/aGraph> { ?s ?p ?o } . }
The access to the graph can be conditional on other information. For example, if the default graph contains metadata about the named graphs in the dataset, then a query like the following one can extract one graph based on information about the named graph:
PREFIX dc: <http://purl.org/dc/elements/1.1/> PREFIX app: <http://example.org/ns#> PREFIX xsd: <http://www.w3.org/2001/XMLSchema#> CONSTRUCT { ?s ?p ?o } WHERE { GRAPH ?g { ?s ?p ?o } . ?g dc:publisher <http://www.w3.org/> . ?g dc:date ?date . FILTER ( app:customDate(?date) > "2005-02-28T00:00:00Z"^^xsd:dateTime ) . }
where app:customDate
identifies an
extension function to turn the date format into an xsd:dateTime
RDF term.
The solution modifiers of a query affect the results of a CONSTRUCT
query. In this example, the output graph from the CONSTRUCT
template
is formed from just two of the solutions from graph pattern matching. The query outputs
a graph with the names of the people with the top two sites, rated by hits. The triples
in the RDF graph are not ordered.
@prefix foaf: <http://xmlns.com/foaf/0.1/> . @prefix site: <http://example.org/stats#> . _:a foaf:name "Alice" . _:a site:hits 2349 . _:b foaf:name "Bob" . _:b site:hits 105 . _:c foaf:name "Eve" . _:c site:hits 181 .
PREFIX foaf: <http://xmlns.com/foaf/0.1/> PREFIX site: <http://example.org/stats#> CONSTRUCT { [] foaf:name ?name } WHERE { [] foaf:name ?name ; site:hits ?hits . } ORDER BY desc(?hits) LIMIT 2
@prefix foaf: <http://xmlns.com/foaf/0.1/> . _:x foaf:name "Alice" . _:y foaf:name "Eve" .
A short form for the CONSTRUCT query form is provided for the case where the template and
the pattern are the same and the pattern is just a basic graph pattern
(no FILTER
s and no complex graph patterns are allowed in the short form).
The keyword WHERE
is required in the short form.
The following two queries are the same; the first is a short form of the second.
PREFIX foaf: <http://xmlns.com/foaf/0.1/> CONSTRUCT WHERE { ?x foaf:name ?name }
PREFIX foaf: <http://xmlns.com/foaf/0.1/> CONSTRUCT { ?x foaf:name ?name } WHERE { ?x foaf:name ?name }
Applications can use the ASK
form to test whether or not a query
pattern has a solution. No information is returned about the possible query solutions,
just whether or not a solution exists.
@prefix foaf: <http://xmlns.com/foaf/0.1/> . _:a foaf:name "Alice" . _:a foaf:homepage <http://work.example.org/alice/> . _:b foaf:name "Bob" . _:b foaf:mbox <mailto:bob@work.example> .
PREFIX foaf: <http://xmlns.com/foaf/0.1/> ASK { ?x foaf:name "Alice" }
true
The SPARQL Query Results XML Format form of this result set gives:
<?xml version="1.0"?> <sparql xmlns="http://www.w3.org/2005/sparql-results#"> <head></head> <boolean>true</boolean> </sparql>
On the same data, the following returns no match because Alice's mbox
is not mentioned.
PREFIX foaf: <http://xmlns.com/foaf/0.1/> ASK { ?x foaf:name "Alice" ; foaf:mbox <mailto:alice@work.example> }
false
The DESCRIBE
form returns a single result RDF graph containing RDF
data about resources. This data is not prescribed by a SPARQL query, where the query
client would need to know the structure of the RDF in the data source, but, instead,
is determined by the SPARQL query processor. The query pattern is used to create
a result set. The DESCRIBE
form takes each of the resources identified
in a solution, together with any resources directly named by IRI, and assembles
a single RDF graph by taking a "description" which can come from any
information available including the target RDF Dataset. The
description is determined by the query service. The syntax DESCRIBE *
is an abbreviation that describes all of the variables in a query.
The DESCRIBE
clause itself can take IRIs to identify the resources.
The simplest DESCRIBE
query is just an IRI in the DESCRIBE
clause:
DESCRIBE <http://example.org/>
The resources to be described can also be taken from the bindings to a query variable in a result set. This enables description of resources whether they are identified by IRI or by blank node in the dataset:
PREFIX foaf: <http://xmlns.com/foaf/0.1/> DESCRIBE ?x WHERE { ?x foaf:mbox <mailto:alice@org> }
The property foaf:mbox
is defined as being an inverse functional property
in the FOAF vocabulary. If treated as such, this query will return information about
at most one person. If, however, the query pattern has multiple solutions, the RDF
data for each is the union of all RDF graph descriptions.
PREFIX foaf: <http://xmlns.com/foaf/0.1/> DESCRIBE ?x WHERE { ?x foaf:name "Alice" }
More than one IRI or variable can be given:
PREFIX foaf: <http://xmlns.com/foaf/0.1/> DESCRIBE ?x ?y <http://example.org/> WHERE {?x foaf:knows ?y}
The RDF returned is determined by the information publisher. It may be information the service deems relevant to the resources being described. It may include information about other resources: for example, the RDF data for a book may also include details about the author.
A simple query such as
PREFIX ent: <http://org.example.com/employees#> DESCRIBE ?x WHERE { ?x ent:employeeId "1234" }
might return a description of the employee and some other potentially useful details:
@prefix foaf: <http://xmlns.com/foaf/0.1/> . @prefix vcard: <http://www.w3.org/2001/vcard-rdf/3.0> . @prefix exOrg: <http://org.example.com/employees#> . @prefixrdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> . @prefix owl: <http://www.w3.org/2002/07/owl#>
_:a exOrg:employeeId "1234" ;foaf:mbox_sha1sum "bee135d3af1e418104bc42904596fe148e90f033" ;
vcard:N [ vcard:Family "Smith" ; vcard:Given "John" ] .foaf:mbox_sha1sum rdf:type owl:InverseFunctionalProperty .
which includes the blank node closure for the vcard vocabulary vcard:N. Other possible mechanisms for deciding what information to return include Concise Bounded Descriptions [CBD].
For a vocabulary such as FOAF, where the resources are typically blank nodes,
returning sufficient information to identify a node such as the InverseFunctionalProperty
foaf:mbox_sha1sum
as well as information like name and other details recorded
would be appropriate. In the example, the match to the WHERE
clause was returned,
but this is not required.
SPARQL FILTERs
restrict the solutions of a graph pattern match according to a given constraint. Specifically,
FILTERs
eliminate any solutions that, when substituted into the expression, either result in an effective boolean value of false
or produce an error. Effective boolean values are defined in section 17.2.2 Effective Boolean Value and errors are defined in XQuery 1.0: An XML Query Language [XQUERY] section 2.3.1, Kinds of Errors. These errors have no effect outside of FILTER
evaluation.
RDF literals may have a datatype IRI:
@prefix a: <http://www.w3.org/2000/10/annotation-ns#> . @prefix dc: <http://purl.org/dc/elements/1.1/> . _:a a:annotates <http://www.w3.org/TR/rdf-sparql-query/> . _:a dc:date "2004-12-31T19:00:00-05:00" . _:b a:annotates <http://www.w3.org/TR/rdf-sparql-query/> . _:b dc:date "2004-12-31T19:01:00-05:00"^^<http://www.w3.org/2001/XMLSchema#dateTime> .
The object of the first dc:date
triple has no type information. The second has the datatype xsd:dateTime
.
SPARQL expressions are constructed according to the grammar and provide access to functions (named by IRI) and operator functions (invoked by keywords and symbols in the SPARQL grammar). SPARQL operators can be used to compare the values of typed literals:
PREFIX a: <http://www.w3.org/2000/10/annotation-ns#> PREFIX dc: <http://purl.org/dc/elements/1.1/> PREFIX xsd: <http://www.w3.org/2001/XMLSchema#> SELECT ?annot WHERE { ?annot a:annotates <http://www.w3.org/TR/rdf-sparql-query/> . ?annot dc:date ?date . FILTER ( ?date > "2005-01-01T00:00:00Z"^^xsd:dateTime ) }
The SPARQL operators are listed in section 17.3 and are associated with their productions in the grammar.
In addition, SPARQL provides the ability to invoke arbitrary functions, including a subset of the XPath casting functions, listed in section 17.5. These functions are invoked by name (an IRI) within a SPARQL query. For example:
... FILTER ( xsd:dateTime(?date) < xsd:dateTime("2005-01-01T00:00:00Z") ) ...
Typographical convention in this section: XPath operators are labeled
with the prefix op:
. XPath operators have no namespace;
op:
is a labeling convention.
SPARQL functions and operators operate on RDF terms and SPARQL variables. A subset of these functions and operators are taken from the XQuery 1.0 and XPath 2.0 Functions and Operators [FUNCOP] and have XML Schema typed value arguments and return types.
RDF typed literals
passed as arguments to these functions and operators are mapped to XML Schema typed values with a string value of the lexical form
and an atomic datatype corresponding to the datatype IRI. The returned typed values are mapped back to RDF typed literals
the same way.
SPARQL has additional operators which operate on specific subsets of RDF terms. When referring to a type, the following terms denote a typed literal
with the corresponding XML Schema [XSDT] datatype IRI:
The following terms identify additional types used in SPARQL value tests:
typed literals
with datatypes xsd:integer
, xsd:decimal
, xsd:float
, and xsd:double
.plain literal
with no language tag
.IRI
, literal
, and blank node
.The following types are derived from numeric types and are valid arguments to functions and operators taking numeric arguments:
xsd:nonPositiveInteger
xsd:negativeInteger
xsd:long
xsd:int
xsd:short
xsd:byte
xsd:nonNegativeInteger
xsd:unsignedLong
xsd:unsignedInt
xsd:unsignedShort
xsd:unsignedByte
xsd:positiveInteger
SPARQL language extensions may treat additional types as being derived from XML schema datatypes.
SPARQL provides a subset of the functions and operators defined by XQuery Operator Mapping. XQuery 1.0 section 2.2.3 Expression Processing describes the invocation of XPath functions. The following rules accommodate the differences in the data and execution models between XQuery and SPARQL:
xsd:boolean
using the EBV rules in section 17.2.2.||
) or logical-and (&&
) that encounters an error will produce that error.The logical-and and logical-or truth table for true (T), false (F), and error (E) is as follows:
A | B | A || B | A && B |
---|---|---|---|
T | T | T | T |
T | F | T | F |
F | T | T | F |
F | F | F | F |
T | E | T | E |
E | T | T | E |
F | E | E | F |
E | F | E | F |
E | E | E | E |
SPARQL defines a syntax for invoking functions on a list of arguments. Unless otherwise noted, these are invoked as follows:
If any of these steps fails, the invocation generates an error. The effects of errors are defined in Filter Evaluation.
There are also "functional forms" which have different evaluation rules to functions as specificed by each such form.
Effective boolean value is used to calculate the arguments to the logical functions logical-and, logical-or, and fn:not, as well as evaluate the result of a FILTER
expression.
The XQuery Effective Boolean Value rules rely on the definition of XPath's fn:boolean. The following rules reflect the rules for fn:boolean
applied to the argument types present in SPARQL queries:
xsd:boolean
or numeric is false if the lexical form is not valid for that datatype (e.g. "abc"^^xsd:integer).xsd:boolean
, and it has a valid lexical form, the EBV is the value of that argument.xsd:string
, the EBV is false if the operand value has zero length; otherwise the EBV is true.An EBV of true
is represented as a typed literal with a datatype of xsd:boolean
and a lexical value of "true"; an EBV of false is represented as a typed literal with a datatype of xsd:boolean
and a lexical value of "false".
The SPARQL grammar identifies a set of operators (for instance, &&, *, isIRI) used to construct constraints. The following table associates each of these grammatical productions with the appropriate operands and an operator function defined by either XQuery 1.0 and XPath 2.0 Functions and Operators [FUNCOP] or the SPARQL operators specified in section 17.4. When selecting the operator definition for a given set of parameters, the definition with the most specific parameters applies. For instance, when evaluating xsd:integer = xsd:signedInt
, the definition for =
with two numeric
parameters applies, rather than the one with two RDF terms. The table is arranged so that the upper-most viable candidate is the most specific. Operators invoked without appropriate operands result in a type error.
SPARQL follows XPath's scheme for numeric type promotions and subtype substitution for arguments to numeric operators. The XPath Operator Mapping rules for numeric operands (xsd:integer
, xsd:decimal
, xsd:float
, xsd:double
, and types derived from a numeric type) apply to SPARQL operators as well (see XML Path Language (XPath) 2.0 [XPATH20] for definitions of numeric type promotions and subtype substitution). Some of the operators are associated with nested function expressions, e.g. fn:not(op:numeric-equal(A, B))
. Note that per the XPath definitions, fn:not
and op:numeric-equal
produce an error if their argument is an error.
The collation for fn:compare
is defined by XPath and identified by http://www.w3.org/2005/xpath-functions/collation/codepoint
. This collation allows for string comparison based on code point values. Codepoint string equivalence can be tested with RDF term equivalence.
Operator | Type(A) | Function | Result type |
---|---|---|---|
XQuery Unary Operators | |||
! A | xsd:boolean (EBV) | fn:not(A) | xsd:boolean |
+ A | numeric | op:numeric-unary-plus(A) | numeric |
- A | numeric | op:numeric-unary-minus(A) | numeric |
Operator | Type(A) | Type(B) | Function | Result type |
---|---|---|---|---|
Logical Connectives | ||||
A || B | xsd:boolean (EBV) | xsd:boolean (EBV) | logical-or(A, B) | xsd:boolean |
A && B | xsd:boolean (EBV) | xsd:boolean (EBV) | logical-and(A, B) | xsd:boolean |
XPath Tests | ||||
A = B | numeric | numeric | op:numeric-equal(A, B) | xsd:boolean |
A = B | simple literal | simple literal | op:numeric-equal(fn:compare(A, B), 0) | xsd:boolean |
A = B | xsd:string | xsd:string | op:numeric-equal(fn:compare(STR(A), STR(B)), 0) | xsd:boolean |
A = B | xsd:boolean | xsd:boolean | op:boolean-equal(A, B) | xsd:boolean |
A = B | xsd:dateTime | xsd:dateTime | op:dateTime-equal(A, B) | xsd:boolean |
A != B | numeric | numeric | fn:not(op:numeric-equal(A, B)) | xsd:boolean |
A != B | simple literal | simple literal | fn:not(op:numeric-equal(fn:compare(A, B), 0)) | xsd:boolean |
A != B | xsd:string | xsd:string | fn:not(op:numeric-equal(fn:compare(STR(A), STR(B)), 0)) | xsd:boolean |
A != B | xsd:boolean | xsd:boolean | fn:not(op:boolean-equal(A, B)) | xsd:boolean |
A != B | xsd:dateTime | xsd:dateTime | fn:not(op:dateTime-equal(A, B)) | xsd:boolean |
A < B | numeric | numeric | op:numeric-less-than(A, B) | xsd:boolean |
A < B | simple literal | simple literal | op:numeric-equal(fn:compare(A, B), -1) | xsd:boolean |
A < B | xsd:string | xsd:string | op:numeric-equal(fn:compare(STR(A), STR(B)), -1) | xsd:boolean |
A < B | xsd:boolean | xsd:boolean | op:boolean-less-than(A, B) | xsd:boolean |
A < B | xsd:dateTime | xsd:dateTime | op:dateTime-less-than(A, B) | xsd:boolean |
A > B | numeric | numeric | op:numeric-greater-than(A, B) | xsd:boolean |
A > B | simple literal | simple literal | op:numeric-equal(fn:compare(A, B), 1) | xsd:boolean |
A > B | xsd:string | xsd:string | op:numeric-equal(fn:compare(STR(A), STR(B)), 1) | xsd:boolean |
A > B | xsd:boolean | xsd:boolean | op:boolean-greater-than(A, B) | xsd:boolean |
A > B | xsd:dateTime | xsd:dateTime | op:dateTime-greater-than(A, B) | xsd:boolean |
A <= B | numeric | numeric | logical-or(op:numeric-less-than(A, B), op:numeric-equal(A, B)) | xsd:boolean |
A <= B | simple literal | simple literal | fn:not(op:numeric-equal(fn:compare(A, B), 1)) | xsd:boolean |
A <= B | xsd:string | xsd:string | fn:not(op:numeric-equal(fn:compare(STR(A), STR(B)), 1)) | xsd:boolean |
A <= B | xsd:boolean | xsd:boolean | fn:not(op:boolean-greater-than(A, B)) | xsd:boolean |
A <= B | xsd:dateTime | xsd:dateTime | fn:not(op:dateTime-greater-than(A, B)) | xsd:boolean |
A >= B | numeric | numeric | logical-or(op:numeric-greater-than(A, B), op:numeric-equal(A, B)) | xsd:boolean |
A >= B | simple literal | simple literal | fn:not(op:numeric-equal(fn:compare(A, B), -1)) | xsd:boolean |
A >= B | xsd:string | xsd:string | fn:not(op:numeric-equal(fn:compare(STR(A), STR(B)), -1)) | xsd:boolean |
A >= B | xsd:boolean | xsd:boolean | fn:not(op:boolean-less-than(A, B)) | xsd:boolean |
A >= B | xsd:dateTime | xsd:dateTime | fn:not(op:dateTime-less-than(A, B)) | xsd:boolean |
XPath Arithmetic | ||||
A * B | numeric | numeric | op:numeric-multiply(A, B) | numeric |
A / B | numeric | numeric | op:numeric-divide(A, B) | numeric; but xsd:decimal if both operands are xsd:integer |
A + B | numeric | numeric | op:numeric-add(A, B) | numeric |
A - B | numeric | numeric | op:numeric-subtract(A, B) | numeric |
SPARQL Tests | ||||
A = B | RDF term | RDF term | RDFterm-equal(A, B) | xsd:boolean |
A != B | RDF term | RDF term | fn:not(RDFterm-equal(A, B)) | xsd:boolean |
xsd:boolean function arguments marked with "(EBV)" are coerced to xsd:boolean by evaluating the effective boolean value of that argument.
SPARQL language extensions may provide additional associations between operators and operator functions; this amounts to adding rows to the table above. No additional operator may yield a result that replaces any result other than a type error in the semantics defined above. The consequence of this rule is that SPARQL FILTER
s will produce at least the same intermediate bindings after applying a FILTER
as an unextended implementation.
Additional mappings of the '<' operator are expected to control the relative ordering of the operands, specifically, when used in an ORDER BY
clause.
This section defines the operators and functions introduced by the SPARQL Query language. The examples show the behavior of the operators as invoked by the appropriate grammatical constructs.
xsd:boolean BOUND (variable var)
Returns true
if var
is bound to a value. Returns false otherwise. Variables with the value NaN or INF are considered bound.
Data:
@prefix foaf: <http://xmlns.com/foaf/0.1/> . @prefix dc: <http://purl.org/dc/elements/1.1/> . @prefix xsd: <http://www.w3.org/2001/XMLSchema#> . _:a foaf:givenName "Alice". _:b foaf:givenName "Bob" . _:b dc:date "2005-04-04T04:04:04Z"^^xsd:dateTime .
PREFIX foaf: <http://xmlns.com/foaf/0.1/> PREFIX dc: <http://purl.org/dc/elements/1.1/> PREFIX xsd: <http://www.w3.org/2001/XMLSchema#> SELECT ?givenName WHERE { ?x foaf:givenName ?givenName . OPTIONAL { ?x dc:date ?date } . FILTER ( bound(?date) ) }
Query result:
givenName |
---|
"Bob" |
One may test that a graph pattern is not expressed by specifying an OPTIONAL graph pattern that introduces a variable and testing to see that the variable is not bound. This is called Negation as Failure in logic programming.
This query matches the people with a name
but no expressed date
:
PREFIX foaf: <http://xmlns.com/foaf/0.1/> PREFIX dc: <http://purl.org/dc/elements/1.1/> SELECT ?name WHERE { ?x foaf:givenName ?name . OPTIONAL { ?x dc:date ?date } . FILTER (!bound(?date)) }
Query result:
name |
---|
"Alice" |
Because Bob's dc:date
was known, "Bob"
was not a solution to the query.
rdfTerm IF (expression1, expression2, expression3)
The IF
function form evaluates the first argument, interprets it as a effective boolean value, then returns the value of expression2
if the EBV is true, otherwise it returns the value of expression3
. Only one of expression2
and expression3
is evaluated.
If evaluating the first argument raises an error,
then an error is raised for the evaluation of the IF
expression.
Examples: Suppose ?x = 2, ?z = 0 and ?y is not bound in some query solution:
IF(?x = 2, "yes", "no") | returns "yes" |
IF(bound(?y), "yes", "no") | returns "no" |
IF(?x=2, "yes", 1/?z) | returns "yes", the expression 1/?z is not evaluated |
IF(?x=1, "yes", 1/?z) | raises an error |
IF("2" > 1, "yes", "no") | raises an error |
rdfTerm COALESCE(expression, ....)
The COALESCE
function form returns the RDF term value
of the first expression that evaluates without error. In SPARQL,
evaluating an unbound variable raises an error.
If none of the arguments evaluates to an RDF term, an error is raised. If no expressions are evaluate without error, an error is raised.
Examples: Suppose ?x = 2, ?z = 0 and ?y is not bound in some query solution:
COALESCE(?x, 1/0) | returns 2, the value of x |
COALESCE(1/0, ?x) | returns 2 |
COALESCE(5, ?x) | returns 5 |
COALESCE(?y, 3) | returns 3 |
COALESCE(?y) | raises an error because y is not bound. |
There is a filter operator EXISTS
that takes a graph pattern.
EXISTS
returns true
/false
depending on whether
the pattern matches the dataset
given the bindings in the current group graph pattern, the dataset and
the active graph at this point in the
query evaluation.
No additional binding of variables occurs. The NOT EXISTS
form
translates into fn:not(EXISTS{...})
.
xsd:boolean NOT EXISTS { pattern }
Returns false
if pattern
matches. Returns true otherwise.
NOT EXISTS { pattern }
is equivalent to fn:not(EXISTS { pattern })
.
xsd:boolean EXISTS
{ pattern }
Returns true
if pattern
matches.
Returns false otherwise.
Variables in the pattern
that are bound in the current
solution mapping take the value that they have from the solution mapping.
Variables in the pattern pattern
that are not bound in the current
solution mapping take part in pattern matching.
To facilitate this, we introduce a function Exists that evaluates a SPARQL Algebra expression and returns true or false, depending on whether there are any solutions to the pattern, given the solution mapping being tested by the filter operation.
xsd:boolean xsd:boolean left || xsd:boolean right
Returns a logical OR
of left
and right
. Note that logical-or operates on the effective boolean value of its arguments.
Note: see section 17.2, Filter Evaluation, for
the ||
operator's treatment of errors.
xsd:boolean xsd:boolean left && xsd:boolean right
Returns a logical AND
of left
and right
. Note that logical-and operates on the effective boolean value of its arguments.
Note: see section 17.2, Filter Evaluation, for
the &&
operator's treatment of errors.
xsd:boolean RDF term term1 = RDF term term2
Returns TRUE if term1
and term2
are the same RDF term as defined in Resource Description Framework (RDF): Concepts and Abstract Syntax [CONCEPTS]; produces a type error if the arguments are both literal but are not the same RDF term *; returns FALSE otherwise. term1
and term2
are the same if any of the following is true:
@prefix foaf: <http://xmlns.com/foaf/0.1/> . _:a foaf:name "Alice". _:a foaf:mbox <mailto:alice@work.example> . _:b foaf:name "Ms A.". _:b foaf:mbox <mailto:alice@work.example> .
This query finds the people who have multiple foaf:name
triples:
PREFIX foaf: <http://xmlns.com/foaf/0.1/> SELECT ?name1 ?name2 WHERE { ?x foaf:name ?name1 ; foaf:mbox ?mbox1 . ?y foaf:name ?name2 ; foaf:mbox ?mbox2 . FILTER (?mbox1 = ?mbox2 && ?name1 != ?name2) }
Query result:
name1 | name2 |
---|---|
"Alice" | "Ms A." |
"Ms A." | "Alice" |
In this query for documents that were annotated at a specific date and time (New Year's Day 2005, measures in timezone +00:00), the RDF terms are not the same, but have equivalent values:
@prefix a: <http://www.w3.org/2000/10/annotation-ns#> . @prefix dc: <http://purl.org/dc/elements/1.1/> . _:b a:annotates <http://www.w3.org/TR/rdf-sparql-query/> . _:b dc:date "2004-12-31T19:00:00-05:00"^^<http://www.w3.org/2001/XMLSchema#dateTime> .
PREFIX a: <http://www.w3.org/2000/10/annotation-ns#> PREFIX dc: <http://purl.org/dc/elements/1.1/> PREFIX xsd: <http://www.w3.org/2001/XMLSchema#> SELECT ?annotates WHERE { ?annot a:annotates ?annotates . ?annot dc:date ?date . FILTER ( ?date = xsd:dateTime("2005-01-01T00:00:00Z") ) }
annotates |
---|
<http://www.w3.org/TR/rdf-sparql-query/> |
* Invoking RDFterm-equal on two typed literals tests for
equivalent values. An extended implementation may have support for additional datatypes. An implementation processing a query that tests for equivalence on unsupported datatypes (and non-identical lexical form and datatype IRI) returns an error, indicating that it was unable to determine whether or not the values are equivalent. For example, an unextended implementation will produce an error when testing either
"iiii"^^my:romanNumeral = "iv"^^my:romanNumeral
or
"iiii"^^my:romanNumeral != "iv"^^my:romanNumeral
.
xsd:boolean sameTerm (RDF term term1, RDF term term2)
Returns TRUE if term1
and term2
are the same RDF term as defined in Resource Description Framework (RDF): Concepts and Abstract Syntax [CONCEPTS]; returns FALSE otherwise.
@prefix foaf: <http://xmlns.com/foaf/0.1/> . _:a foaf:name "Alice". _:a foaf:mbox <mailto:alice@work.example> . _:b foaf:name "Ms A.". _:b foaf:mbox <mailto:alice@work.example> .
This query finds the people who have multiple foaf:name
triples:
PREFIX foaf: <http://xmlns.com/foaf/0.1/> SELECT ?name1 ?name2 WHERE { ?x foaf:name ?name1 ; foaf:mbox ?mbox1 . ?y foaf:name ?name2 ; foaf:mbox ?mbox2 . FILTER (sameTerm(?mbox1, ?mbox2) && !sameTerm(?name1, ?name2)) }
Query result:
name1 | name2 |
---|---|
"Alice" | "Ms A." |
"Ms A." | "Alice" |
Unlike RDFterm-equal, sameTerm can be used to test for non-equivalent typed literals with unsupported datatypes:
@prefix : <http://example.org/WMterms#> . @prefix t: <http://example.org/types#> . _:c1 :label "Container 1" . _:c1 :weight "100"^^t:kilos . _:c1 :displacement "100"^^t:liters . _:c2 :label "Container 2" . _:c2 :weight "100"^^t:kilos . _:c2 :displacement "85"^^t:liters . _:c3 :label "Container 3" . _:c3 :weight "85"^^t:kilos . _:c3 :displacement "85"^^t:liters .
PREFIX : <http://example.org/WMterms#> PREFIX t: <http://example.org/types#> SELECT ?aLabel1 ?bLabel WHERE { ?a :label ?aLabel . ?a :weight ?aWeight . ?a :displacement ?aDisp . ?b :label ?bLabel . ?b :weight ?bWeight . ?b :displacement ?bDisp . FILTER ( sameTerm(?aWeight, ?bWeight) && !sameTerm(?aDisp, ?bDisp)) }
aLabel | bLabel |
---|---|
"Container 1" | "Container 2" |
"Container 2" | "Container 1" |
The test for boxes with the same weight may also be done with the '=' operator (RDFterm-equal) as the test for "100"^^t:kilos = "85"^^t:kilos
will result in an error, eliminating that potential solution.
boolean rdfTerm
IN (expression, ...)
The IN
operator tests whether the RDF term on the
left-hand side is found in the values of list of expressions
on the right-hand side.
The test is done with "=" operator, which tests for the same value, as
determined by the operator mapping.
A list of zero terms on the right-hand side is legal.
Errors in comparisons cause the IN
expression
to raise an error if the RDF term being tested is not found
elsewhere in the list of terms.
The IN
operator is equivalent to the SPARQL expression:
(lhs = expression1) || (lhs = expression2) || ...
Examples:
2 IN (1, 2, 3) | true |
2 IN () | false |
2 IN (<http://example/iri>, "str", 2.0) | true |
2 IN (1/0, 2) | true |
2 IN (2, 1/0) | true |
2 IN (3, 1/0) | raises an error |
boolean rdfTerm
NOT IN (expression, ...)
The NOT IN
operator tests whether the RDF term on the
left-hand side is not found in the values of list of expressions
on the right-hand side.
The test is done with "!=" operator, which tests for not the same value, as
determined by the operator mapping.
A list of zero terms on the right-hand side is legal.
Errors in comparisons cause the NOT IN
expression
to raise an error if the RDF term being tested is not found
to be in the list elsewhere in the list of terms.
The NOT IN
operator is equivalent to the SPARQL expression:
(lhs != expression1) && (lhs != expression2) && ...
NOT IN (...)
is equivalent to !(IN (...))
.
Examples:
2 NOT IN (1, 2, 3) | false |
2 NOT IN () | true |
2 NOT IN (<http://example/iri>, "str", 2.0) | false |
2 NOT IN (1/0, 2) | false |
2 NOT IN (2, 1/0) | false |
2 NOT IN (3, 1/0) | raises an error |
xsd:boolean isIRI (RDF term term) xsd:boolean isURI (RDF term term)
Returns true
if term
is an IRI. Returns false
otherwise. isURI is an alternate spelling for the isIRI operator.
@prefix foaf: <http://xmlns.com/foaf/0.1/> . _:a foaf:name "Alice". _:a foaf:mbox <mailto:alice@work.example> . _:b foaf:name "Bob" . _:b foaf:mbox "bob@work.example" .
This query matches the people with a name
and an mbox
which is an IRI:
PREFIX foaf: <http://xmlns.com/foaf/0.1/> SELECT ?name ?mbox WHERE { ?x foaf:name ?name ; foaf:mbox ?mbox . FILTER isIRI(?mbox) }
Query result:
name | mbox |
---|---|
"Alice" | <mailto:alice@work.example> |
xsd:boolean isBlank (RDF term term)
Returns true
if term
is a blank node. Returns false
otherwise.
@prefix a: <http://www.w3.org/2000/10/annotation-ns#> . @prefix dc: <http://purl.org/dc/elements/1.1/> . @prefix foaf: <http://xmlns.com/foaf/0.1/> . _:a a:annotates <http://www.w3.org/TR/rdf-sparql-query/> . _:a dc:creator "Alice B. Toeclips" . _:b a:annotates <http://www.w3.org/TR/rdf-sparql-query/> . _:b dc:creator _:c . _:c foaf:given "Bob". _:c foaf:family "Smith".
This query matches the people with a dc:creator
which uses
predicates from the FOAF vocabulary to express the name.
PREFIX a: <http://www.w3.org/2000/10/annotation-ns#> PREFIX dc: <http://purl.org/dc/elements/1.1/> PREFIX foaf: <http://xmlns.com/foaf/0.1/> SELECT ?given ?family WHERE { ?annot a:annotates <http://www.w3.org/TR/rdf-sparql-query/> . ?annot dc:creator ?c . OPTIONAL { ?c foaf:given ?given ; foaf:family ?family } . FILTER isBlank(?c) }
Query result:
given | family |
---|---|
"Bob" | "Smith" |
In this example, there were two objects of dc:creator
predicates, but only one (_:c
) was a blank node.
xsd:boolean isLiteral (RDF term term)
Returns true
if term
is a literal. Returns false
otherwise.
@prefix foaf: <http://xmlns.com/foaf/0.1/> . _:a foaf:name "Alice". _:a foaf:mbox <mailto:alice@work.example> . _:b foaf:name "Bob" . _:b foaf:mbox "bob@work.example" .
This query is similar to the one in 17.4.2.1 except that is matches the people with a name
and an mbox
which is a literal. This could be used to look for erroneous data (foaf:mbox
should only have an
IRI as its object).
PREFIX foaf: <http://xmlns.com/foaf/0.1/> SELECT ?name ?mbox WHERE { ?x foaf:name ?name ; foaf:mbox ?mbox . FILTER isLiteral(?mbox) }
Query result:
name | mbox |
---|---|
"Bob" | "bob@work.example" |
xsd:boolean isNumeric (RDF term term)
Returns true
if term
is a numeric value. Returns false
otherwise.
term
is numeric if it has an appropriate datatype (see the section Operand Data Types) and has a valid lexical form, making it
a valid argument to functions and operators
taking numeric arguments.
Examples:
isNumeric(12) | true |
isNumeric("12") | false |
isNumeric("12"^^xsd:nonNegativeInteger) | true |
isNumeric("1200"^^xsd:byte) | false |
isNumeric(<http://example/>) | false |
simple literal STR (literal ltrl) simple literal STR (IRI rsrc)
Returns the lexical form of ltrl
(a literal); returns the codepoint representation of rsrc
(an IRI). This is useful for examining parts of an IRI, for instance, the host-name.
@prefix foaf: <http://xmlns.com/foaf/0.1/> . _:a foaf:name "Alice". _:a foaf:mbox <mailto:alice@work.example> . _:b foaf:name "Bob" . _:b foaf:mbox <mailto:bob@home.example> .
This query selects the set of people who use their work.example
address in their foaf profile:
PREFIX foaf: <http://xmlns.com/foaf/0.1/> SELECT ?name ?mbox WHERE { ?x foaf:name ?name ; foaf:mbox ?mbox . FILTER regex(str(?mbox), "@work\\.example$") }
Query result:
name | mbox |
---|---|
"Alice" | <mailto:alice@work.example> |
simple literal LANG (literal ltrl)
Returns the language tag of ltrl
, if it has one. It returns ""
if ltrl
has no language tag. Note that the RDF data model does not include literals with an empty language tag.
@prefix foaf: <http://xmlns.com/foaf/0.1/> . _:a foaf:name "Robert"@en. _:a foaf:name "Roberto"@es. _:a foaf:mbox <mailto:bob@work.example> .
This query finds the Spanish foaf:name
and foaf:mbox
:
PREFIX foaf: <http://xmlns.com/foaf/0.1/> SELECT ?name ?mbox WHERE { ?x foaf:name ?name ; foaf:mbox ?mbox . FILTER ( lang(?name) = "es" ) }
Query result:
name | mbox |
---|---|
"Roberto"@es | <mailto:bob@work.example> |
iri DATATYPE (literal literal)
Returns the datatype IRI of a literal
.
xsd:string
rdf:langString
@prefix foaf: <http://xmlns.com/foaf/0.1/> . @prefix eg: <http://biometrics.example/ns#> . @prefix xsd: <http://www.w3.org/2001/XMLSchema#> . _:a foaf:name "Alice". _:a eg:shoeSize "9.5"^^xsd:float . _:b foaf:name "Bob". _:b eg:shoeSize "42"^^xsd:integer .
This query finds the foaf:name
and foaf:shoeSize
of everyone with a shoeSize that is an integer:
PREFIX foaf: <http://xmlns.com/foaf/0.1/> PREFIX xsd: <http://www.w3.org/2001/XMLSchema#> PREFIX eg: <http://biometrics.example/ns#> SELECT ?name ?shoeSize WHERE { ?x foaf:name ?name ; eg:shoeSize ?shoeSize . FILTER ( datatype(?shoeSize) = xsd:integer ) }
Query result:
name | shoeSize |
---|---|
"Bob" | 42 |
In SPARQL 1.0, the
DATATYPE
function was not defined for literals with a language tag.
Therefore, an unextended implementation would raise an error when DATATYPE
was called with a literal with a language tag. Operator extensibility allows implementations to
return a result rather than raise an error. SPARQL 1.1 defines the result of
DATATYPE
applied to a literal with a language tag to be
rdf:langString
.
rdf:langString
based on the work in RDF-WG.
iri IRI(simple literal
) iri IRI(xsd:string) iri IRI(iri) iri URI(simple literal
) iri URI(xsd:string) iri URI(iri)
The IRI
function constructs an IRI by resolving the string argument
(see RFC 3986
and RFC 3987
or any later RFC that superceeds RFC 3986 or RFC 3987).
The IRI is resolved against the base IRI of the query and must result
in an absolute IRI.
The URI
function is a synonym for IRI
.
If the function is passed an IRI, it returns the IRI unchanged.
Passing any RDF term other than a simple literal, xsd:string or an IRI is an error.
An implementation MAY normalize the IRI.
Examples:
IRI("http://example/") | <http://example/> |
IRI(<http://example/>) | <http://example/> |
blank node BNODE()
blank node BNODE(simple literal)
blank node BNODE(xsd:string)
The BNODE
function constructs a blank node that is distinct
from all blank nodes in the dataset being queried and distinct
from all blank nodes created by calls to this constructor
for other query solutions. If the no argument form is used,
every call results in a distinct blank node. If the form with
a simple literal is used, every call results in distinct blank nodes
for different simple literals, and the same blank node
for calls with the same simple literal within expressions for
one solution mapping.
This functionality is compatible with the treatment of blank nodes in SPARQL CONSTRUCT templates.
literal STRDT(simple literal lexicalForm, IRI datatypeIRI)
The STRDT
function constructs a literal with lexical
form and type as specified by the arguments.
STRDT("123", xsd:integer) | "123"^^<http://www.w3.org/2001/XMLSchema#integer> |
STRDT("iiii", <http://example/romanNumeral>) | "iiii"^^<http://example/romanNumeral> |
Certain functions (e.g. REGEX,
STRLEN, CONTAINS)
take a string literal
as an argument and accept a simple literal,
a plain literal with language tag, or a literal with datatype xsd:string.
They then act on the lexcial form of the literal.
The term string literal
is used in the function descriptions for this.
Use of any other RDF term will cause a call to the function to raise an error.
The functions STRSTARTS, STRENDS, CONTAINS, STRBEFORE and STRAFTER take two arguments. These arguments must be compatible otherwise invocation of one of these functions raises an error.
Compatibility of two arguments is defined as:
Argument1 | Argument2 | Compatible? |
---|---|---|
"abc" | "b" | yes |
"abc" | "b"^^xsd:string | yes |
"abc"^^xsd:string | "b" | yes |
"abc"^^xsd:string | "b"^^xsd:string | yes |
"abc"@en | "b" | yes |
"abc"@en | "b"^^xsd:string | yes |
"abc"@en | "b"@en | yes |
"abc"@fr | "b"@ja | no |
"abc" | "b"@ja | no |
"abc" | "b"@en | no |
"abc"^^xsd:string | "b"@en | no |
Functions that return a string literal do so with the string literal of the same kind as the first argument (simple literal, plain literal with same language tag, xsd:string). This includes SUBSTR, STRBEFORE and STRAFTER.
The function CONCAT returns a string literal based on the details of all its arguments.
xsd:integer STRLEN(string literal str)
The strlen
function corresponds to the
XPath fn:string-length
function and returns an xsd:integer
equal to the length
in characters of the lexical form of the literal.
strlen("chat") | 4 |
strlen("chat"@en) | 4 |
strlen("chat"^^xsd:string) | 4 |
string literal SUBSTR(string literal source, xsd:integer startingLoc)
string literal SUBSTR(string literal source, xsd:integer startingLoc, xsd:integer length)
The substr
function corresponds to the XPath
fn:substring
function and returns a literal of the same kind (simple literal, literal with language tag,
xsd:string
typed literal) as the source
input parameter but
with a lexical form formed from the substring of the lexcial form of the source.
The arguments startingLoc
and length
may be derived types of xsd:integer.
The index of the first character in a strings is 1.
substr("foobar", 4) | "bar" |
substr("foobar"@en, 4) | "bar"@en |
substr("foobar"^^xsd:string, 4) | "bar"^^xsd:string |
substr("foobar", 4, 1) | "b" |
substr("foobar"@en, 4, 1) | "b"@en |
substr("foobar"^^xsd:string, 4, 1) | "b"^^xsd:string |
string literal UCASE(string literal str)
The UCASE
function corresponds to the XPath
fn:upper-case function.
It returns a string literal whose lexical form is the upper case of the
lexcial form of the argument.
ucase("foo") | "FOO" |
ucase("foo"@en) | "FOO"@en |
ucase("foo"^^xsd:string) | "FOO"^^xsd:string |
string literal LCASE(string literal str)
The LCASE
function corresponds to the XPath
fn:lower-case function.
It returns a string literal whose lexical form is the lower case of the
lexcial form of the argument.
lcase("BAR") | "bar" |
lcase("BAR"@en) | "bar"@en |
lcase("BAR"^^xsd:string) | "bar"^^xsd:string |
xsd:boolean STRSTARTS(string literal arg1, string literal arg2)
The STRSTARTS
function corresponds to the XPath
fn:starts-with function.
The arguments must be argument compatible
otherwise an error is raised.
For such input pairs, the function returns true if the lexical form of arg1
starts with the lexical form of arg2
, otherwise it returns false.
strStarts("foobar", "foo") | true |
strStarts("foobar"@en, "foo"@en) | true |
strStarts("foobar"^^xsd:string, "foo"^^xsd:string) | true |
strStarts("foobar"^^xsd:string, "foo") | true |
strStarts("foobar", "foo"^^xsd:string) | true |
strStarts("foobar"@en, "foo") | true |
strStarts("foobar"@en, "foo"^^xsd:string) | true |
xsd:boolean STRENDS(string literal arg1, string literal arg2)
The STRENDS
function corresponds to the XPath
fn:starts-with function.
The arguments must be argument compatible
otherwise an error is raised.
For such input pairs, the function returns true if the lexical form of arg1
ends with the lexical form of arg2
, otherwise it returns false.
strEnds("foobar", "bar") | true |
strEnds("foobar"@en, "bar"@en) | true |
strEnds("foobar"^^xsd:string, "bar"^^xsd:string) | true |
strEnds("foobar"^^xsd:string, "bar") | true |
strEnds("foobar", "bar"^^xsd:string) | true |
strEnds("foobar"@en, "bar") | true |
strEnds("foobar"@en, "bar"^^xsd:string) | true |
xsd:boolean CONTAINS(string literal arg1, string literal arg2)
The CONTAINS
function corresponds to the XPath
fn:contains.
The arguments must be argument compatible
otherwise an error is raised.
contains("foobar", "bar") | true |
contains("foobar"@en, "foo"@en) | true |
contains("foobar"^^xsd:string, "bar"^^xsd:string) | true |
contains("foobar"^^xsd:string, "foo") | true |
contains("foobar", "bar"^^xsd:string) | true |
contains("foobar"@en, "foo") | true |
contains("foobar"@en, "bar"^^xsd:string) | true |
literal STRBEFORE(string literal arg1, string literal arg2)
The STRBEFORE
function corresponds to the XPath
fn:substring-before function.
The arguments must be argument compatible
otherwise an error is raised.
The function returns a literal of the same kind
(simple literal, plain literal same language tag, xsd:string)
as the first argument arg1
. The lexical form of
the result is the substring of the value of arg1
that precedes in arg1
the first occurrence of
the lexical form of arg2
;
otherwise the lexical form of the result is the empty string.
If the lexical form of arg2
is the empty string,
the lexical form of the result is the emprty string.
strbefore("abc","b") | "a" |
strbefore("abc"@en,"bc") | "a"@en |
strbefore("abc"@en,"b"@cy) | error |
strbefore("abc"^^xsd:string,"") | ""^^xsd:string |
strbefore("abc","xyz") | "" |
literal STRAFTER(string literal arg1, string literal arg2)
The STRAFTER
function corresponds to the XPath
fn:substring-after function.
The arguments must be argument compatible
otherwise an error is raised.
The function returns a literal of the same kind
(simple literal, plain literal same language tag, xsd:string)
as the first argument arg1
. The lexical form of
the result is the substring of the value of arg1
that proceeds in arg1
the first occurrence of
the lexical form of arg2
;
otherwise the lexical form of the result is the empty string.
If the lexical form of arg2
is the empty string,
the lexical form of the result is the emprty string.
strafter("abc","b") | "c" |
strafter("abc"@en,"ab") | "c"@en |
strafter("abc"@en,"b"@cy) | error |
strafter("abc"^^xsd:string,"") | ""^^xsd:string |
strafter("abc","xyz") | "" |
simple literal ENCODE_FOR_URI(string literal ltrl)
The ENCODE_FOR_URI
function corresponds to the XPath fn:encode-for-uri function.
It returns a simple literal with the lexical form obtained from the lexical
form of its input after translating reserved characters according to the
fn:encode-for-uri function.
encode_for_uri("Los Angeles") | "Los%20Angeles" |
encode_for_uri("Los Angeles"@en) | "Los%20Angeles" |
encode_for_uri("Los Angeles"^^xsd:string) | "Los%20Angeles" |
string literal CONCAT(string literal ltrl1 ... string literal ltrln)
The CONCAT
function corresponds to the XPath fn:concat function. The function accepts string literals as arguments.
The lexical form of the returned literal is obtained by concatenating the lexical forms of its inputs.
If all input literals are typed literals of type xsd:string
, then the returned literal is also of type xsd:string
, if all input literals are plain literals with identical language tag, then the returned literal is a plain literal with the same language tag, in all other cases, the returned literal is a simple literal.
concat("foo", "bar") | "foobar" |
concat("foo"@en, "foo"@en) | "foobar"@en |
concat("foo"^^xsd:string, "bar"^^xsd:string) | "foobar"^^xsd:string |
concat("foo", "bar"^^xsd:string) | "foobar" |
concat("foo"@en, "foo") | "foobar" |
concat("foo"@en, "bar"^^xsd:string) | "foobar" |
xsd:boolean langMatches (simple literal language-tag, simple literal language-range)
Returns true
if language-tag
(first argument) matches language-range
(second argument) per the basic filtering scheme defined in [RFC4647] section 3.3.1. language-range
is a basic language range per Matching of Language Tags [RFC4647] section 2.1. A language-range
of "*" matches any non-empty language-tag
string.
@prefix dc: <http://purl.org/dc/elements/1.1/> . _:a dc:title "That Seventies Show"@en . _:a dc:title "Cette Série des Années Soixante-dix"@fr . _:a dc:title "Cette Série des Années Septante"@fr-BE . _:b dc:title "Il Buono, il Bruto, il Cattivo" .
This query uses
langMatches
and
lang
to find the French titles for the show known in English as "That Seventies Show":
PREFIX dc: <http://purl.org/dc/elements/1.1/> SELECT ?title WHERE { ?x dc:title "That Seventies Show"@en ; dc:title ?title . FILTER langMatches( lang(?title), "FR" ) }
Query result:
title |
---|
"Cette Série des Années Soixante-dix"@fr |
"Cette Série des Années Septante"@fr-BE |
The idiom langMatches( lang( ?v ), "*" )
will not match literals without a language tag as lang( ?v )
will return an empty string, so
PREFIX dc: <http://purl.org/dc/elements/1.1/> SELECT ?title WHERE { ?x dc:title ?title . FILTER langMatches( lang(?title), "*" ) }
will report all of the titles with a language tag:
title |
---|
"That Seventies Show"@en |
"Cette Série des Années Soixante-dix"@fr |
"Cette Série des Années Septante"@fr-BE |
xsd:boolean REGEX (string literal text, simple literal pattern) xsd:boolean REGEX (string literal text, simple literal pattern, simple literal flags)
Invokes the XPath fn:matches function to match text
against a regular expression pattern
. The regular expression language is defined in XQuery 1.0 and XPath 2.0 Functions and Operators section 7.6.1 Regular Expression Syntax [FUNCOP].
@prefix foaf: <http://xmlns.com/foaf/0.1/> . _:a foaf:name "Alice". _:b foaf:name "Bob" .
PREFIX foaf: <http://xmlns.com/foaf/0.1/> SELECT ?name WHERE { ?x foaf:name ?name FILTER regex(?name, "^ali", "i") }
Query result:
name |
---|
"Alice" |
string literal REPLACE (string literal arg, simple literal pattern, simple literal replacement ) string literal REPLACE (string literal arg, simple literal pattern, simple literal replacement, simple literal flags)
The REPLACE
function corresponds to the XPath
fn:replace function.
It replaces each non-overlapping occurrence of the regular expression pattern with the replacement string.
Regular expession matching may involve modifier flags. See REGEX.
replace("abcd", "b", "Z") | "aZcd" |
replace("abab", "B", "Z","i") | "aZaZ" |
replace("abab", "B.", "Z","i") | "aZb" |
numeric ABS (numeric term)
Returns the absolute value of arg
.
An error is raised if arg
is not a numeric value.
This function is the same as fn:numeric-abs for terms with a datatype from XDM.
abs(1) | 1 |
abs(-1.5) | 1.5 |
numeric ROUND (numeric term)
Returns the number with no fractional part that is closest to the argument.
If there are two such numbers, then the one that is closest to
positive infinity is returned.
An error is raised if arg
is not a numeric value.
This function is the same as fn:numeric-round for terms with a datatype from XDM.
round(2.4999) | 2.0 |
round(2.5) | 3.0 |
round(-2.5) | -2.0 |
numeric CEIL (numeric term)
Returns the smallest (closest to negative infinity) number
with no fractional part that is not less than the value of arg
.
An error is raised if arg
is not a numeric value.
This function is the same as fn:numeric-ceil for terms with a datatype from XDM.
ceil(10.5) | 11.0 |
ceil(-10.5) | -10.0 |
numeric FLOOR (numeric term)
Returns the largest (closest to positive infinity) number
with no fractional part that is not greater than the value of arg
.
An error is raised if arg
is not a numeric value.
This function is the same as fn:numeric-floor for terms with a datatype from XDM.
floor(10.5) | 10.0 |
floor(-10.5) | -11.0 |
xsd:dateTime NOW ()
Returns an XSD dateTime value for the current query execution. All calls to this function in any one query execution must return the same value. The exact moment returned is not specificed.
now() | "2011-01-10T14:45:13.815-05:00"^^xsd:dateTime |
xsd:integer YEAR (xsd:dateTime arg)
Returns the year part of arg
as an integer.
This function corresponds to fn:year-from-dateTime.
year("2011-01-10T14:45:13.815-05:00"^^xsd:dateTime) | 2011 |
xsd:integer MONTH (xsd:dateTime arg)
Returns the month part of arg
as an integer.
This function corresponds to fn:month-from-dateTime.
month("2011-01-10T14:45:13.815-05:00"^^xsd:dateTime) | 1 |
xsd:integer DAY (xsd:dateTime arg)
Returns the day part of arg
as an integer.
This function corresponds to fn:day-from-dateTime.
day("2011-01-10T14:45:13.815-05:00"^^xsd:dateTime) | 10 |
xsd:integer HOURS (xsd:dateTime arg)
Returns the hours part of arg
as an integer.
The value is as given in the lexical form of the XSD dateTime.
This function corresponds to fn:hours-from-dateTime.
hours("2011-01-10T14:45:13.815-05:00"^^xsd:dateTime) | 14 |
xsd:integer MINUTES (xsd:dateTime arg)
Returns the minutes part of the lexical form of arg
.
The value is as given in the lexical form of the XSD dateTime.
This function corresponds to fn:minutes-from-dateTime.
minutes("2011-01-10T14:45:13.815-05:00"^^xsd:dateTime) | 45 |
xsd:decimal SECONDS (xsd:dateTime arg)
Returns the seconds part of the lexical form of arg
.
This function corresponds to fn:seconds-from-dateTime.
seconds("2011-01-10T14:45:13.815-05:00"^^xsd:dateTime) | 13.815 |
xsd:duration TIMEZONE (xsd:dateTime arg)
Returns the timezone part of arg
as an xsd:dayTimeDuration.
Raises an error if there is no timezone.
This function corresponds to fn:timezone-from-dateTime except for the treatment of literals with no timezone.
timezone("2011-01-10T14:45:13.815-05:00"^^xsd:dateTime) | "-PT5H"^^xsd:dayTimeDuration |
timezone("2011-01-10T14:45:13.815Z"^^xsd:dateTime) | "PT0S"^^xsd:dayTimeDuration |
timezone("2011-01-10T14:45:13.815"^^xsd:dateTime) | error |
simple literal TZ (xsd:dateTime arg)
Returns the timezone part of arg
as a simple literal.
Returns the empty string if there is no timezone.
tz("2011-01-10T14:45:13.815-05:00"^^xsd:dateTime) | "-05:00" |
tz("2011-01-10T14:45:13.815Z"^^xsd:dateTime) | "Z" |
tz("2011-01-10T14:45:13.815"^^xsd:dateTime) | "" |
simple literal MD5 (simple literal arg)
simple literal MD5 (xsd:string arg)
Returns the MD5 checksum, as a hex digit string, calculated on the
UTF-8 representation of the simple literal or lexical form of the
xsd:string
. Hex digits SHOULD be in lower case.
MD5("abc") | "900150983cd24fb0d6963f7d28e17f72" |
MD5("abc"^^xsd:string) | "900150983cd24fb0d6963f7d28e17f72" |
simple literal SHA1 (simple literal arg)
simple literal SHA1 (xsd:string arg)
Returns the SHA1 checksum, as a hex digit string, calculated on the
UTF-8 representation of the simple literal or lexical form of the
xsd:string
. Hex digits SHOULD be in lower case.
SHA1("abc") | "a9993e364706816aba3e25717850c26c9cd0d89d" |
SHA1("abc"^^xsd:string) | "a9993e364706816aba3e25717850c26c9cd0d89d" |
simple literal SHA256 (simple literal arg)
simple literal SHA256 (xsd:string arg)
Returns the SHA256 checksum, as a hex digit string, calculated on the
UTF-8 representation of the simple literal or lexical form of the
xsd:string
. Hex digits SHOULD be in lower case.
SHA256("abc") | "ba7816bf8f01cfea414140de5dae2223b00361a396177a9cb410ff61f20015ad" |
SHA256("abc"^^xsd:string) | "ba7816bf8f01cfea414140de5dae2223b00361a396177a9cb410ff61f20015ad" |
simple literal SHA384 (simple literal arg)
simple literal SHA384 (xsd:string arg)
Returns the SHA384 checksum, as a hex digit string, calculated on the
UTF-8 representation of the simple literal or lexical form of the
xsd:string
. Hex digits SHOULD be in lower case.
SHA384("abc") | "cb00753f45a35e8bb5a03d699ac65007272c32ab0eded1631a8b605a43ff5bed8086072ba1e7cc2358baeca134c825a7" |
SHA384("abc"^^xsd:string) | "cb00753f45a35e8bb5a03d699ac65007272c32ab0eded1631a8b605a43ff5bed8086072ba1e7cc2358baeca134c825a7" |
simple literal SHA512 (simple literal arg)
simple literal SHA512 (xsd:string arg)
Returns the SHA512 checksum, as a hex digit string, calculated on the
UTF-8 representation of the simple literal or lexical form of the
xsd:string
. Hex digits SHOULD be in lower case.
SHA512("abc") | "ddaf35a193617abacc417349ae20413112e6fa4e89a97ea20a9eeee64b55d39a2192992a274fc1a836ba3c23a3feebbd454d4423643ce80e2a9ac94fa54ca49f" |
SHA512("abc"^^xsd:string) | "ddaf35a193617abacc417349ae20413112e6fa4e89a97ea20a9eeee64b55d39a2192992a274fc1a836ba3c23a3feebbd454d4423643ce80e2a9ac94fa54ca49f" |
SPARQL imports a subset of the XPath constructor functions defined in XQuery 1.0 and XPath 2.0 Functions and Operators [FUNCOP] in section 17.1 Casting from primitive types to primitive types. SPARQL constructors include all of the XPath constructors for the SPARQL operand datatypes plus the additional datatypes imposed by the RDF data model. Casting in SPARQL is performed by calling a constructor function for the target type on an operand of the source type.
XPath defines only the casts from one XML Schema datatype to another. The remaining casts are defined as follows:
xsd:string
produces a typed literal with a lexical value of the codepoints comprising the IRI, and a datatype of xsd:string
.xsd:string
with the string value equal to the lexical value of the literal to the target datatype.The table below summarizes the casting operations that are always allowed (Y), never allowed (N) and dependent on the lexical value (M). For example, a casting operation from an xsd:string
(the first row) to an xsd:float
(the second column) is dependent on the lexical value (M).
bool = xsd:boolean
dbl = xsd:double
flt = xsd:float
dec = xsd:decimal
int = xsd:integer
dT = xsd:dateTime
str = xsd:string
IRI = IRI
ltrl =simple literal
From \ To | str | flt | dbl | dec | int | dT | bool |
---|---|---|---|---|---|---|---|
str | Y | M | M | M | M | M | M |
flt | Y | Y | Y | M | M | N | Y |
dbl | Y | Y | Y | M | M | N | Y |
dec | Y | Y | Y | Y | Y | N | Y |
int | Y | Y | Y | Y | Y | N | Y |
dT | Y | N | N | N | N | Y | N |
bool | Y | Y | Y | Y | Y | N | Y |
IRI | Y | N | N | N | N | N | N |
ltrl | Y | M | M | M | M | M | M |
It should be noted that any function or operator that is specified to return an error under some conditions is a valid extension point. That is, an implementation may return a non-error value in these error cases, and still be conformant with this recommendation.
A PrimaryExpression grammar rule can be a call to an extension function named by an IRI. An extension function takes some number of RDF terms as arguments and returns an RDF term. The semantics of these functions are identified by the IRI that identifies the function.
SPARQL queries using extension functions are likely to have limited interoperability.
As an example, consider a function called func:even
:
xsd:boolean
func:even
(numeric
value
)
This function would be invoked in a FILTER as such:
PREFIX foaf: <http://xmlns.com/foaf/0.1/> PREFIX func: <http://example.org/functions#> SELECT ?name ?id WHERE { ?x foaf:name ?name ; func:empId ?id . FILTER (func:even(?id)) }
For a second example, consider a function aGeo:distance
that calculates the distance between two points, which is used here to find the places near Grenoble:
xsd:double
aGeo:distance
(numeric
x1
,numeric
y1
,numeric
x2
,numeric
y2
)
PREFIX aGeo: <http://example.org/geo#> SELECT ?neighbor WHERE { ?a aGeo:placeName "Grenoble" . ?a aGeo:location ?axLoc . ?a aGeo:location ?ayLoc . ?b aGeo:placeName ?neighbor . ?b aGeo:location ?bxLoc . ?b aGeo:location ?byLoc . FILTER ( aGeo:distance(?axLoc, ?ayLoc, ?bxLoc, ?byLoc) < 10 ) . }
An extension function might be used to test some application datatype not supported by the core SPARQL specification, it might be a transformation between datatype formats, for example into an XSD dateTime RDF term from another date format.
This section defines the correct behavior for evaluation of graph patterns and solution modifiers, given a query string and an RDF dataset. It does not imply a SPARQL implementation must use the process defined here.
The outcome of executing a SPARQL query is defined by a series of steps, starting from the SPARQL query as a string, turning that string into an abstract syntax form, then turning the abstract syntax into a SPARQL abstract query comprising operators from the SPARQL algebra. This abstract query is then evaluated on an RDF dataset.
SPARQL is defined in terms of IRIs [RFC3987]. IRIs are a subset of RDF URI References that omits the use of spaces.
Let I be the set of all IRIs.
Let RDF-L be the set of all RDF Literals
Let RDF-B be the set of all blank nodes in RDF graphs
The set of RDF Terms, RDF-T, is I ∪ RDF-L ∪ RDF-B.
This definition of RDF Term collects together several basic notions from the RDF data model, but updated to refer to IRIs rather than RDF URI references.
Definition: Simple Literal
The set of Simple Literals is the set of all RDF Literals with no language tag or datatype IRI.
An RDF dataset is a set:
{ G, (<u1>, G1), (<u2>, G2), . . .
(<un>, Gn) }
where G and each Gi are graphs, and each <ui> is
an IRI.
Each <ui> is distinct.
G is called the default graph. (<ui>, Gi) are called named graphs.
The active graph is the graph from the dataset used for basic graph pattern matching.
Let DS1 =
{ G1, (<u11>, G11), (<u12>, G12), . . .
(<u1n>, G1n) },
and DS2 =
{ G2, (<u21>, G21), (<u22>, G22), . . .
(<u2m>, G2m) }
then we define the RDF Dataset Merge of DS1 and DS2 to be:
DS={ G, (<u1>, G1), (<u2>, G2), . . .
(<uk>, Gk) }
where:
Write N1 for { <u1j> j = 1 to n }
Write N2 for { <u2j> j = 1 to m }
A query variable is a member of the set V where V is infinite and disjoint from RDF-T.
A triple pattern is member of the set:
(RDF-T ∪ V) x (I ∪ V) x (RDF-T ∪ V)
This definition of Triple Pattern includes literal subjects. This has been noted by RDF-core.
"[The RDF core Working Group] noted that it is aware of no reason why literals should not be subjects and a future WG with a less restrictive charter may extend the syntaxes to allow literals as the subjects of statements."
Because RDF graphs may not contain literal subjects, any SPARQL triple pattern with a literal as subject will fail to match on any RDF graph.
A Basic Graph Pattern is a set of Triple Patterns.
The empty graph pattern is a basic graph pattern which is the empty set.
A Property Path is a sequence of triples, ti in sequence ST, with n = length(ST)-1, such that, for i=0 to n, the object of ti is the same term as the subject of ti+1.
We call the subject of t0 the start of the path.
We call the object of tn the end of the path.
A Property Path is a path in graph G if each ti is a triple of G.
A property path does not span multiple graphs in a dataset.
A property path expression is an expression used to match properties in a graph formed after translation of the path syntax as defined below.
Let PP be the set of all property path expressions.
A property path pattern is a member of the set:
(RDF-T ∪ V) x PP x (RDF-T ∪ V)
A Property Path Pattern is a generalization of a Triple Pattern to include a property path expression in the property position.
A solution mapping is a mapping from a set of variables to a set of RDF terms. We use the term 'solution' where it is clear.
A solution mapping, μ, is a partial function μ : V -> RDF-T.
The domain of μ, dom(μ), is the subset of V where μ is defined.
A solution sequence is a list of solutions, possibly unordered.
Write expr(μ) for the value of the expression expr, using the terms for variables given by μ. Evaluation may result in an error.
A solution sequence modifier is one of:
A SPARQL Abstract Query is a tuple (E, DS, QF) where:
A query level is a graph pattern, a set of group and aggregation, and a set of solution modifiers.
A query is a tree of "query levels", where each subquery forms one query level in the tree.
This section defines the process of converting graph patterns and solution modifiers in a SPARQL query string into a SPARQL algebra expression. The process described converts one level of query nesting, as formed by subqueries using the nested SELECT syntax and is applied recursively on subqueries. Each level consists of graph pattern matching and filtering, followed by the application of solution modifiers.
The SPARQL query string is parsed and the abbreviations for IRIs and triple patterns given in section 4 are applied. At this point the abstract syntax tree is composed of:
Patterns | Modifiers | Query Forms | Other |
---|---|---|---|
RDF terms | DISTINCT | SELECT | BINDINGS |
Property path expression | REDUCED | CONSTRUCT | SERVICE |
Property path patterns | Projection | DESCRIBE | |
Groups | ORDER BY | ASK | |
OPTIONAL | LIMIT | ||
UNION | OFFSET | ||
GRAPH | Select expressions | ||
BIND | |||
GROUP BY | |||
HAVING | |||
MINUS | |||
FILTER |
Property path expressions are written to produce triple patterns and algebra forms, ZeroLengthPath, ZeroOrMorePath, OneOrMorePath, and NegatedPropertySet as necessary.
The result of converting such an abstract syntax tree is a SPARQL query that uses the following symbols in the SPARQL algebra:
Graph Pattern | Solution Modifiers |
---|---|
BGP | ToList |
Join | OrderBy |
LeftJoin | Project |
Filter | Distinct |
Union | Reduced |
Graph | Slice |
Extend | ToMultiSet |
Minus | |
Group | |
Aggregation | |
AggregateJoin | |
ZeroLengthPath | |
ZeroOrMorePath | |
OneOrMorePath | |
NegatedPropertySet |
Slice is the combination of OFFSET and LIMIT.
ToList is used where conversion from the results of graph pattern matching to sequences occurs.
ToMultiSet is used where conversion from a solution sequence to a multiset occurs.
ZeroLengthPath, ZeroOrMorePath, OneOrMorePath and NegatedPropertySet are used in property path expressions.
We define a variable to be in-scope if there is a way for a variable to be in the domain of a solution mapping at that point in the execution of the SPARQL algebra for the query. The definition below provides a way of determing this from the abstract syntax of a query.
Note that a subquery with a projection can hide variables;
use of a variable in FILTER
, or in MINUS
does not cause a variable
to be in-scope outside of those forms.
Let P, P1, P2 be graph patterns and E, E1,...En be expressions.
A variable v
is in-scope if:
Syntax Form | In-scope variables |
---|---|
Basic Graph Pattern (BGP) | v occurs in the BGP |
Path | v occurs in the path |
Group { P1 P2 ... } | v is in-scope if it is in-scope in one or more of P1, P2, ... |
GRAPH term { P } | v is term or v is in-scope in P |
{ P1 } UNION { P2 } | v is in-scope in P1 or in-scope in P2 |
OPTIONAL {P} | v is in-scope in P |
SERVICE term {P} | v is term or v is in-scope in P |
(expr AS v) for BIND , SELECT and GROUP BY | v is in-scope |
SELECT ..v .. { P } | v is in-scope if v is mentioned as a project variable |
SELECT * { P } | v is in-scope in P |
BINDINGS varlist (values) | v is in-scope if v is in varlist |
The scoping for (expr AS v)
applies immediately. In
SELECT
expressions, the variable may be used in an expression
later in the same SELECT
clause and may not be
assigned again in the same SELECT
clause.
This section describes the process for translating a SPARQL graph pattern into a SPARQL algebra expression. After translating syntactic abbreviations for IRIs and triple patterns, it recursively processes syntactic forms into algebra expressions.
We write
translate(graph pattern)
for the algorthm described here to translate graph patterns.
OPTIONAL { { ... FILTER ( ... ?x ... ) } }.
.
This is illustrated by two non-normative test cases:
Applying the simpification step after all the translation of graph patterns is the preferred reading.
Expand abbreviations for IRIs and triple patterns given in section 4.
The following table gives the translation of property paths. It is applied recursively to the path syntax. This introduces triple patterns, which are grouped into basic graph patterns by adjacency (without intervening group pattern delimiters { and }) or other syntax forms.
Notes:
We introduce the following symbols:
The parsing step interprets triple patterns as property paths of length 1. This step introduces triple patterns and basic graph patterns.
Syntax Form (path) | translate(path) |
---|---|
X iri Y | Triple pattern: X iri Y |
X !(:iri1|...|:irin) Y | NegatedPropertySet(X,{:iri1 ... :irin} ,Y) |
X !(^:iri1|...|^:irin)Y | X ^(!(:iri1|...|:irin)) Y |
X !(:iri1|...|:irii|^:irii+1|...|^:irim) Y | { X !(:iri1|...|:irii)Y } UNION { X !(^:irii+1|...|^:irim) Y } |
X ^path Y | Y path X |
X path1 / path2 Y | X path1 ?V . ?V path2 Y |
X path1 | path2 Y | { X path1 Y } UNION { X path2 Y} |
X path? Y | { X path{0} Y } UNION { X path Y} |
X path* Y | ZeroOrMorePath(X, path, Y) |
X path+ Y | OneOrMorePath(X, path, Y) |
X path{0} Y | ZeroLengthPath(X, path, Y) |
X path{n} Y where n > 0 | X path ?V1 . ?V1 path ?V2 ... ?Vn-1 path Y |
X path{n,m} Y | { X path{n} Y } UNION { X path{n+1} Y } ... UNION { X path{m} Y} |
X path{n,} Y where n > 0 | X path{n} ?V . ?V path* Y |
X path{0,} Y | X path* Y |
X path{,n} Y | X path{0,n} Y |
After translating property paths, any adjacent triple patterns are collected together
to form a basic graph pattern BGP(triples)
.
In SPARQL 1.0, this was achieved by translating each TriplesBlock.
Replace all occurrences of EXISTS
and
NOT EXISTS
with:
Let P := graph pattern of EXISTS Let A := Translate(P) Replace EXISTS{P} by exists(A) Replace NOT EXISTS{P} by fn:not(exists(A))
Next, translate each graph pattern form, recursively applying the translation process.
If the form is
GroupOrUnionGraphPattern
Let A := undefined For each element G in the GroupOrUnionGraphPattern If A is undefined A := Translate(G) Else A := Union(A, Translate(G)) End The result is A
If the form is
GraphGraphPattern
If the form is GRAPH IRI GroupGraphPattern The result is Graph(IRI, Translate(GroupGraphPattern))
If the form is GRAPH Var GroupGraphPattern The result is Graph(Var, Translate(GroupGraphPattern))
If the form is
GroupGraphPattern
We introduce the following symbols:
- Join(Pattern, Pattern)
- LeftJoin(Pattern, Pattern, expression)
- Filter(expression, Pattern)
Let FS := the empty set Let G := the empty pattern, a basic graph pattern which is the empty set. For each element E in the GroupGraphPattern If E is of the form FILTER(expr) FS := FS ∪ {expr} End If E is of the form OPTIONAL{P} Let A := Translate(P) If A is of the form Filter(F, A2) G := LeftJoin(G, A2, F) Else G := LeftJoin(G, A, true) End End If E is of the form MINUS{P} G := Minus(G, Translate(P)) End If E is of the form BIND(expr AS var) G := Extend(G, var, expr) End If E is any other form Let A := Translate(E) G := Join(G, A) End End If FS is not empty Let X := Conjunction of expressions in FS G := Filter(X, G) End The result is G.
If the form is SubSelect
The result is ToMultiset(Translate(SubSelect))
The second form of a rewrite example is the first with empty group joins removed by the simplification step.
Example: group with a basic graph pattern consisting of a single triple pattern:
Example: group with a basic graph pattern consisting of two triple patterns:
Example: group consisting of a union of two basic graph patterns:
Example: group consisting of a union of a union and a basic graph pattern:
Example: group consisting of a basic graph pattern and an optional graph pattern:
Example: group consisting of a basic graph pattern and two optional graph patterns:
Example: group consisting of a basic graph pattern and an optional graph pattern with a filter:
Example: group consisting of a union graph pattern and an optional graph pattern:
Example: group consisting of a basic graph pattern, a filter and an optional graph pattern:
Example: Pattern involving BIND:
Example: Pattern involving MINUS:
Example: Pattern involving a subquery:
In this step, we process clauses on the query level in the following order:
Step: GROUP BY
If the GROUP BY
keyword is used, or there is implicit grouping due to the use of aggregates in the projection, then grouping is performed by the Group function. It divides the solution set into groups of one or more solutions, with the same overall cardinality. In case of implicit grouping, a fixed constant (1) is used to group all solutions into a single group.
Step: Aggregates
The aggregation step is applied as a transformation on the query level, replacing aggregate expressions in the query level with Aggregation() algebraic expressions.
The transformation for query levels that use any aggregates is given below:
Let A := the empty sequence Let Q := the query level being evaluated Let P := the algebra translation of the GroupGraphPattern of the query level Let E := [], a list of pairs of the form (variable, expression) If Q contains GROUP BY exprlist Let G := Group(exprlist, P) Else If Q contains an aggregate in SELECT, HAVING, ORDER BY Let G := Group((1), P) Else skip the rest of the aggregate step End Global i := 1 # Initially 1 for each query processed For each (X AS Var) in SELECT, each HAVING(X), and each ORDER BY X in Q For each unaggregated variable V in X Replace V with Sample(V) End For each aggregate R(args ; scalarvals) now in X # note scalarvals may be omitted, then it's equivalent to the empty set Ai := Aggregation(args, R, scalarvals, G) Replace R(...) with aggi in Q i := i + 1 End End For each variable V appearing outside of an aggregate Ai := Aggregation(V, Sample, {}, G) E := E append (V, aggi) i := i + 1 End A := Ai, ..., Ai-1 P := AggregateJoin(A)
Note: aggi is a temporary variable. E is then used in 18.2.4.4 for the processing of select expressions.
Example:
PREFIX rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> SELECT (SUM(?val) AS ?sum) (COUNT(?a) AS ?count) WHERE { ?a rdf:value ?val . } GROUP BY ?a
The SUM expression becomes agg1, and the COUNT expression becomes agg2.
Let G := Group((?a), BGP(?a rdf:value ?val)) A1 = Aggregation((?val), Sum, {}, G) A2 = Aggregation((?a), Count, {}, G) A := (A1, A2) Let P := AggregateJoin(A)
The HAVING expression is evaluated using the same rules as FILTER(). Note that, due to the logic position in which the HAVING clause is evaluated, expressions projected by the SELECT clause are not visible to the HAVING clause.
Let Q := the query level being evaluated Let P := the algebra translation of the query level so far For each HAVING(E) in Q P := Filter(E, P) End
If the query contains a BINDINGS clause:
Let P := the algebra translation of the query level so far P := Join(P, ToMultiSet(data)) where data is a solution sequence formed from the BINDINGS clause.
data is formed from a clause( 'BINDINGS' Var* '{' ( '(' BindingValue* ')' | NIL )* '}' )?
by taking eachBindingValue
, forming the solution mapping from the variable in the corresponding position inVar*
, omitting if theBindingValue
is wordUNDEF
.
Step: Select expressions
We have two forms of the abstract syntax to consider:
SELECT selItem ... { pattern } SELECT * { pattern }
Let X := algebra from earlier steps
Let VS := list of all variables visible in the pattern,
so restricted by sub-SELECT projected variables and GROUP BY variables.
Not visible: only in filter, exists/not exists, masked by a subselect,
non-projected GROUP variables, only in the right hand side of MINUS
Let PV := {}, a set of variable names
Note, E is a list of pairs of the form (variable, expression), defined in section 18.2.4
If "SELECT *"
PV := VS
If "SELECT selItem ...
:"
For each selItem:
If selItem is a variable
PV := PV ∪ { variable }
End
If selItem is (expr AS variable)
variable must not appear in VS nor in PV; if it does then generate a syntax error and stop
PV := PV ∪ { variable }
E := E append (variable, expr)
End
End
For each pair (var, expr) in E
X := Extend(X, var, expr)
End
Result is X
The set PV is used later for projection.
The syntax error arises for use of a variable as the named target of AS (e.g. ... AS ?x) when the variable is used inside the WHERE clause of the SELECT or if already used as the traget of AS in this SELECT expression.
Solutions modifiers apply to the processing of a SPARQL query after pattern matching. The solution modifiers are applied to a query in the following order:
Step: ToList
ToList turns a multiset into a sequence with the same elements and cardinality. There is no implied ordering to the sequence; duplicates need not be adjacent.
Let M := ToList(Pattern)
If the query string has an ORDER BY clause
M := OrderBy(M, list of order comparators)
The set of projection variables, PV
, was calculated in the
processing of SELECT expressions.
M := Project(M, PV)
where vars is the set of variables mentioned in the SELECT clause or all named variables that are in-scope in the query if SELECT * used.
When matching graph patterns, the possible solutions form a multiset [multiset], also known as a bag. A multiset is an unordered collection of elements in which each element may appear more than once. It is described by a set of elements and a cardinality function giving the number of occurrences of each element from the set in the multiset.
Write μ for solution mappings.
Write μ0 for the mapping such that dom(μ0) is the empty set.
Write Ω0 for the multiset consisting of exactly the empty mapping μ0, with cardinality 1. This is the join identity.
Write μ(x) for the solution mapping variable x to RDF term t : { (x, t) }
Write Ω(x) for the multiset consisting of exactly μ(?x->t), that is, { { (x, t) } } with cardinality 1.
Two solution mappings μ1 and μ2 are compatible if, for every variable v in dom(μ1) and in dom(μ2), μ1(v) = μ2(v).
Here, μ1(v) = μ2(v) means that μ1(v) and μ2(v) are the same RDF term.
If μ1 and μ2 are compatible then μ1 ∪ μ2 is also a mapping. Write merge(μ1, μ2) for μ1 ∪ μ2
Write card[Ω](μ) for the cardinality of solution mapping μ in a multiset of mappings Ω.
A basic graph pattern is matched against the active graph for that part of the query. Basic graph patterns can be instantiated by replacing both variables and blank nodes by terms, giving two notions of instance. Blank nodes are replaced using an RDF instance mapping, σ, from blank nodes to RDF terms; variables are replaced by a solution mapping from query variables to RDF terms.
A Pattern Instance Mapping, P, is the combination of an RDF instance mapping, σ, and solution mapping, μ. P(x) = μ(σ(x))
For a BGP 'x', P(x) denotes the result of replacing blank nodes b in x for which σ is defined with σ(b) and all variables v in x for which μ is defined with μ(v).
Any pattern instance mapping defines a unique solution mapping and a unique RDF instance mapping obtained by restricting it to query variables and blank nodes respectively.
Let BGP be a basic graph pattern and let G be an RDF graph.
μ is a solution for BGP from G when there is a pattern instance mapping P such that P(BGP) is a subgraph of G and μ is the restriction of P to the query variables in BGP.
card[Ω](μ) = card[Ω](number of distinct RDF instance mappings, σ, such that P = μ(σ) is a pattern instance mapping and P(BGP) is a subgraph of G).
If a basic graph pattern is the empty set, then the solution is Ω0.
This definition allows the solution mapping to bind a variable in a basic graph pattern, BGP, to a blank node in G. Since SPARQL treats blank node identifiers in a results format document (SPARQL Query Results XML Format, SPARQL 1.1 Query Results JSON Format and SPARQL 1.1 Query Results CSV and TSV Formats) as scoped to the document, they cannot be understood as identifying nodes in the active graph of the dataset. If DS is the dataset of a query, pattern solutions are therefore understood to be not from the active graph of DS itself, but from an RDF graph, called the scoping graph, which is graph-equivalent to the active graph of DS but shares no blank nodes with DS or with BGP. The same scoping graph is used for all solutions to a single query. The scoping graph is purely a theoretical construct; in practice, the effect is obtained simply by the document scope conventions for blank node identifiers.
Since RDF blank nodes allow infinitely many redundant solutions for many patterns, there can be infinitely many pattern solutions (obtained by replacing blank nodes by different blank nodes). It is necessary, therefore, to somehow delimit the solutions for a basic graph pattern. SPARQL uses the subgraph match criterion to determine the solutions of a basic graph pattern. There is one solution for each distinct pattern instance mapping from the basic graph pattern to a subset of the active graph.
This is optimized for ease of computation rather than redundancy elimination. It allows query results to contain redundancies even when the active graph of the dataset is lean, and it allows logically equivalent datasets to yield different query results.
For each symbol in a SPARQL abstract query, we define an operator for evaluation. The SPARQL algebra operators of the same name are used to evaluate SPARQL abstract query nodes as described in the section "Evaluation Semantics".
Definition: Filter
Let Ω be a multiset of solution mappings and expr be an expression. We define:
Filter(expr, Ω, D(G)) = { μ | μ in Ω and expr(μ) is an expression that has an effective boolean value of true }
card[Filter(expr, Ω, D(G))](μ) = card[Ω](μ)
Note that evaluating an exists(pattern)
expression uses the dataset and active graph, D(G).
See the evaluation of filter.
Definition: Join
Let Ω1 and Ω2 be multisets of solution mappings. We define:
Join(Ω1, Ω2) = { merge(μ1, μ2) | μ1 in Ω1and μ2 in Ω2, and μ1 and μ2 are compatible }
card[Join(Ω1, Ω2)](μ) =
for each merge(μ1, μ2), μ1
in Ω1and μ2 in Ω2 such that μ = merge(μ1, μ2),
sum over (μ1, μ2), card[Ω1](μ1)*card[Ω2](μ2)
It is possible that a solution mapping μ in a Join can arise in different solution mappings, μ1and μ2 in the multisets being joined. The cardinality of μ is the sum of the cardinalities from all possibilities.
Definition: Diff
Let Ω1 and Ω2 be multisets of solution mappings and expr be an expression. We define:
Diff(Ω1, Ω2, expr) = { μ | μ in Ω1 such that ∀ μ′ in Ω2, either μ and μ′ are not compatible or μ and μ' are compatible and expr(merge(μ, μ')) has an effective boolean value of false }
card[Diff(Ω1, Ω2, expr)](μ) = card[Ω1](μ)
Diff is used internally for the definition of LeftJoin.
Definition: LeftJoin
Let Ω1 and Ω2 be multisets of solution mappings and expr be an expression. We define:
LeftJoin(Ω1, Ω2, expr) = Filter(expr, Join(Ω1, Ω2)) ∪ Diff(Ω1, Ω2, expr)
card[LeftJoin(Ω1, Ω2, expr)](μ) = card[Filter(expr, Join(Ω1, Ω2))](μ) + card[Diff(Ω1, Ω2, expr)](μ)
Written in full that is:
LeftJoin(Ω1, Ω2, expr) =
{ merge(μ1, μ2) | μ1 in Ω1 and μ2 in
Ω2, μ1 and μ2 are compatible and expr(merge(μ1,
μ2)) is true }
∪
{ μ1 | μ1 in Ω1, ∀ μ2 in Ω2,
μ1 and μ2 are not compatible, or Ω2 is empty }
∪
{ μ1 | μ1 in Ω1, ∃ μ2 in Ω2,
μ1 and μ2 are compatible and expr(merge(μ1, μ2)) is false. }
As these are distinct, the cardinality of LeftJoin is cardinality of these individual components of the definition.
Definition: Union
Let Ω1 and Ω2 be multisets of solution mappings. We define:
Union(Ω1, Ω2) = { μ | μ in Ω1 or μ in Ω2 }
card[Union(Ω1, Ω2)](μ) = card[Ω1](μ) + card[Ω2](μ)
Definition: Minus
Let Ω1 and Ω2 be multisets of solution mappings. We define:
Minus(Ω1, Ω2) = { μ | μ in Ω1 . ∀ μ' in Ω2, either μ and μ' are not compatible or dom(μ) and dom(μ') are disjoint }
card[Minus(Ω1, Ω2)](μ) = card[Ω1](μ)
The additional restriction on dom(μ) and dom(μ') is added because otherwise
if there is a solution mapping in Ω2 that has no variables in
common with the solution mappings of Ω1, then
Minus(Ω1, Ω2) would be empty, regardless of
the rest of Ω2. The empty solution mapping is compatible
with every other solution mapping so P MINUS {}
would otherwise
be empty for any pattern P
.
There are 4 property path operators in the SPARQL algebra
Definition: ZeroLengthPath
A zero length path matches all subjects and objects in the graph, and also any RDF terms explicitly given as endpoints of the path pattern.
Definition: ZeroOrMorePath
An arbitrary length path P = (X (path)* Y) is all solutions from X to Y by repeated use of path such that any nodes in the graph are traversed once only. ZeroOrMorePath includes X.
Definition: OneOrMorePath
An arbitrary length path P = (X (path)+ Y) is all solutions from X to Y by repeated use of path such that any nodes in the graph are traversed once only. This does not include X, unless repeated evaluation of the path from X returns to X.
A NegatedPropertySet NPS(X, S, Y), where X and Y are variables or RDF terms, and S is a set of IRIs, describes a match where X and Y are the subject and object respectively of a triple but the property IRI of the triple is not one of the IRIs in S.
Let μ be a solution mapping, Ω a multiset of solution mappings, var a variable and expr be an expression, then we define:
Extend(μ, var, expr) = μ ∪ { (var,value) | var not in dom(μ) and value = expr(μ) }
Extend(μ, var, expr) = μ if var not in dom(μ) and expr(μ) is an error
Extend is undefined when var in dom(μ).
Extend(Ω, var, expr) = { Extend(μ, var, expr) | μ in Ω }
Write [ x | C ] for a sequence of elements where C is a condition on x.
Write card[L](x) to be the cardinality of x in L.
Let Ω be a multiset of solution mappings. We define:
ToList(Ω) = a sequence of mappings μ in Ω in any order, with card[Ω](μ) occurrences of μ
card[ToList(Ω)](μ) = card[Ω](μ)
Let Ψ be a sequence of solution mappings. We define:
OrderBy(Ψ, condition) = [ μ | μ in Ψ and the sequence satisfies the ordering condition]
card[OrderBy(Ψ, condition)](μ) = card[Ψ](μ)
Let Ψ be a sequence of solution mappings and PV a set of variables.
For mapping μ, write Proj(μ, PV) to be the restriction of μ to variables in PV.
Project(Ψ, PV) = [ Proj(Ψ[μ], PV) | μ in Ψ ]
card[Project(Ψ, PV)](μ) = card[Ψ](μ)
The order of Project(Ψ, PV) must preserve any ordering given by OrderBy.
Let Ψ be a sequence of solution mappings. We define:
Distinct(Ψ) = [ μ | μ in Ψ ]
card[Distinct(Ψ)](μ) = 1
The order of Distinct(Ψ) must preserve any ordering given by OrderBy.
Let Ψ be a sequence of solution mappings. We define:
Reduced(Ψ) = [ μ | μ in Ψ ]
card[Reduced(Ψ)](μ) is between 1 and card[Ψ](μ)
The order of Reduced(Ψ) must preserve any ordering given by OrderBy.
The Reduced solution sequence modifier does not guarantee a defined cardinality.
Let Ψ be a sequence of solution mappings. We define:
Slice(Ψ, start, length)[i] = Ψ[start+i] for i = 0 to (length-1)
Let Ψ be a solution sequence. We define:
ToMultiSet(Ψ) = { μ | μ in Ψ }
card[ToMultiSet(Ψ)](μ) = card[Ψ](μ)
ListEval is a function which is used to evaluate a list of expressions against a solution and return a list of the resulting values.
ToMultiset turns a sequence into a multiset with the same elements and cardinality as the sequence. The order of the sequence has no effect on the resulting multiset, and duplicates are preserved.
Definition: Exists
exists(pattern) is a function that returns true if the pattern evaluates to a non-empty solution sequence, given the current solution mapping and active graph at the time of evaluation; otherwise it returns false.
Group is a function which groups a solution sequence into multiple solutions, based on some attribute of the solutions.
Group evaluates a list of expressions against a solution sequence, producing a set of partial functions from keys to solution sequences.
Group(exprlist, Ω) = { ListEval(exprlist, μ) → { μ' | μ' in Ω, ListEval(exprlist, μ) = ListEval(exprlist, μ') } | μ in Ω }
Definition: ListEval
ListEval((expr1, ..., exprn), μ) returns a list (e1, ..., en), where ei = expri(μ) or error.
ListEval retains errors resulting from the evaluation of the list elements.
Note that, although the result of a ListEval can be an error, and errors may be used to group, solutions containing error values are removed at projection time.
ListEval((unbound), μ) = (error), as the evaluation of an unbound expression is an error.
Aggregation, a function which calculates a scalar value as an output of the aggregate expression. It is used in the SELECT clause, the HAVING evaluation process, and in ORDER BY (where required). Aggregation calculates aggregated values over groups of solutions, using set functions.
Let exprlist be a list of expressions or *, func a set function, scalarvals a set of partial functions (possibly empty) passed from the aggregate in the query, and let { key1→Ω1, ..., keym→Ωm } be a multiset of partial functions from keys to solution sequences as produced by the grouping step.
Aggregation applies the set function func to the given multiset and produces a single value for each key and partition of solutions for that key.
Aggregation(exprlist, func, scalarvals, { key1→Omega1, ..., keym→Omegam } )
= { (key, F(Ω)) | key → Ω in { key1→Ω1, ..., keym→Ωm } }
where
M(Ω) = { ListEval(exprlist, μ) | μ in Ω }
F(Ω) = func(M(Ω), scalarvals), for non-DISTINCT
F(Ω) = func(Distinct(M(Ω)), scalarvals), for DISTINCT
Special Case: when COUNT
is used with the expression *
the value of F
will be the cardinality of the group solution sequence,
card[Ω]
, or card[Distinct(Ω)]
if the DISTINCT
keyword is
present.
scalarvals are used to pass values to the underlying set function,
bypassing the mechanics of the grouping. For example, the aggregate
expression GROUP_CONCAT(?x ; separator="|")
has a scalarvals argument
of { "separator" → "|" }.
All aggregates may have the DISTINCT
keyword as the first token in their argument list. If this keyword is
present then first argument to func is Distinct(M).
Example
Given a solution multiset (Ω) with the following values:
solution | ?x | ?y | ?z |
μ1 | 1 | 2 | 3 |
μ2 | 1 | 3 | 4 |
μ3 | 2 | 5 | 6 |
And the query expression SELECT (ex:agg(?y, ?z) AS ?agg) WHERE { ?x ?y ?z } GROUP BY ?x.
We produce G = Group((?x), Ω) = { ( (1), { μ1, μ2 } ), ( (2), { μ3 } ) }
And so Aggregation((?y, ?z), ex:agg, {}, G) =
{ ((1), eg:agg({(2, 3), (3, 4)}, {})), ((2), eg:agg({(5, 6)}, {})) }.
Definition: AggregateJoin
Let S1, ..., Sn be a list of sets, where each set Si contains key to (aggregated) value maps as produced by Aggregate.
Let K = { key | key in dom(Sj) for some 1 <= j <= n } be the set of keys, then
AggregateJoin(S1, ..., Sn) = { agg1→val1, ..., aggn→valn | key in K and key→vali in Si for each 1 <= i <= n }
Flatten is a function which is used to collapse multisets of lists into a multiset, so for example { (1, 2), (3, 4) } becomes { 1, 2, 3, 4 }.
Definition: Flatten
The Flatten(M) function takes a multiset of lists, M {(L1, L2, ...), ...}, and returns the multiset { x | L in M and x in L }.
The set functions which underlie SPARQL aggregates all have a common
signature: SetFunc(M), or SetFunc(M, scalarvals) where M is a multiset
of lists, and scalarvals is one or more scalar values that are passed to the
set function indirectly via the ( ... ; key=value ) syntax for aggregates in the SPARQL grammar. The only use of this that is supported by the built-in aggregates in SPARQL Query 1.1 is GROUP_CONCAT
, as in GROUP_CONCAT(?x ; separator=", ")
.
Note that the name "Set Function" is somewhat historical — the arguments to set functions are in fact multisets. The name is retained due to the commonality with SQL Set Functions, which also operate over multisets.
The set functions defined in this document are Count, Sum, Min, Max, Avg, GroupConcat, and Sample — corresponding to the aggregates COUNT
, SUM
, MIN
, MAX
, AVG
, GROUP_CONCAT
, and SAMPLE
. Definitions may be found in the following sections. Systems may choose to expand this set using local extensions, using the same notation as for functions and casts. Note that, unless the ; separator is used this requires the parser to know whether some IRI refers to a function, cast, or aggregate before it can determine if there are any errors in a query where aggregates are used.
Count is a SPARQL set function which counts the number of times a given expression has a bound, and non-error value within the aggregate group.
Definition: Count
xsd:integer Count(multiset M)N = Flatten(M)
remove error elements from N
Count(M) = card[N]
Sum is a SPARQL set function that will return the numeric value obtained by summing the values within the aggregate group. Type promotion happens as per the op:numeric-add function, applied transitively, (see definition below) so the value of SUM(?x), in an aggregate group where ?x has values 1 (integer), 2.0e0 (float), and 3.0 (decimal) will be 6.0 (float).
Definition: Sum
numeric Sum(multiset M)The Sum set function is used by the SUM
aggregate in the syntax.
Sum(M) = Sum(ToList(Flatten(M))).
Sum(S) = op:numeric-add(S1, Sum(S2..n)) when card[S] > 1
Sum(S) = op:numeric-add(S1, 0) when card[S] = 1
Sum(S) = "0"^^xsd:integer when card[S] = 0
In this way, Sum({1, 2, 3}) = op:numeric-add(1, op:numeric-add(2, op:numeric-add(3, 0))).
The Avg set function calculates the average value for an expression over a group. It is defined in terms of Sum and Count.
Definition: Avg
numeric Avg(multiset M)Avg(M) = "0"^^xsd:integer, where Count(M) = 0
Avg(M) = Sum(M) / Count(M), where Count(M) > 0
For example, Avg({1, 2, 3}) = Sum({1, 2, 3})/Count({1, 2, 3}) = 6/3 = 2.
Min is a SPARQL set functions that returns the minimum value from a group respectively.
It makes use of the SPARQL ORDER BY ordering definition, to allow ordering over arbitrarily typed expressions.
Definition: Min
term Min(multiset M)Min(M) = Min(ToList(Flatten(M))).
The flattened multiset of values passed as an argument is converted to a sequence S, this sequence is ordered as per the ORDER BY ASC
clause.
Min(S) = S0
Max is a SPARQL set function that return the maximum value from a group respectively.
It makes use of the SPARQL ORDER BY ordering definition, to allow ordering over arbitrarily typed expressions.
Definition: Max
term Max(multiset M)Max(M) = Max(ToList(Flatten(M))).
The multiset of values passed as an argument is converted to a sequence S, this sequence is ordered as per the ORDER BY DESC
clause.
Max(S) = S0
GroupConcat is a set function which performs a string concatenation across the values of an expression with a group. The order of the strings is not specified. The separator character used in the concatenation may be given with the scalar argument SEPARATOR.
Definition: GroupConcat
literal GroupConcat(multiset M)If the "separator" scalar argument is absent from GROUP_CONCAT then it is taken to be the "space" character, unicode codepoint U+0020.
The multiset of values, M passed as an argument is converted to a sequence S.
GroupConcat(M, scalarvals) = GroupConcat(Flatten(M), scalarvals("separator"))
GroupConcat(S, sep) = "", where |S| = 0
GroupConcat(S, sep) = CONCAT("", S0), where |S| = 1
GroupConcat(S, sep) = CONCAT(S0, sep, GroupConcat(S1..n-1, sep)), where |S| > 1
For example, GroupConcat({"a", "b", "c"}, {"separator" → "."}) = "a.b.c".
Sample is a set function which returns an arbitrary value from the multiset passed to it.
Definition: Sample
literal Sample(multiset M)Sample(M) = v, where v in Flatten(M)
For example, given Sample({"a", "b", "c"}), "a", "b", and "c" are all valid return values. Note that Sample() is not required to be deterministic for a given input, the only restriction is that the output value must be present in the input multiset.
We define eval(D(G), algebra expression) as the evaluation of an algebra expression with respect to a dataset D having active graph G. The active graph is initially the default graph.
D : a dataset D(G) : D a dataset with active graph G (the one patterns match against) D[i] : The graph with IRI i in dataset D P, P1, P2 : graph patterns L : a solution sequence F : an expression
eval(D(G), BGP) = multiset of solution mappings
See section Basic Graph Patterns
eval(D(G), Filter(F, P)) = Filter(F, eval(D(G),P), D(G))
'substitute' is a filter function in support of the evaluation of
EXISTS
and NOT EXISTS
forms which were translated to exists
.
Definition: Substitute
Let μ be a solution mapping.
substitute(pattern, μ) = the pattern formed by replacing every occurrence of a variable v in pattern by μ(v) for each v in dom(μ)
Definition: Evaluation of Exists
Let μ be the current solution mapping for a filter and P a graph pattern:
The value exists(P), given D(G) is true if and only if eval(D(G), substitute(P, μ)) is a non-empty sequence.
eval(D(G), Join(P1, P2)) = Join(eval(D(G), P1), eval(D(G), P2))
eval(D(G), LeftJoin(P1, P2, F)) = LeftJoin(eval(D(G), P1), eval(D(G), P2), F)
eval(D(G), Union(P1,P2)) = Union(eval(D(G), P1), eval(D(G), P2))
if IRI is a graph name in D eval(D(G), Graph(IRI,P)) = eval(D(D[IRI]), P)
if IRI is not a graph name in D eval(D(G), Graph(IRI,P)) = the empty multiset
eval(D(G), Graph(var,P)) = Let R be the empty multiset foreach IRI i in D R := Union(R, Join( eval(D(D[i]), P) , Ω(?var->i) ) the result is R
The evaluation of graph uses the SPARQL algebra union operator. The cardinality of a solution mapping is the sum of the cardinalities of that solution mapping in each join operation.
Definition: Evaluation of Group
eval(D(G), Group(exprlist, P)) = Group(exprlist, eval(D(G), P))
Definition: Evaluation of Aggregation
eval(D(G), Aggregation(exprlist, func, scalarvals, P)) = Aggregation(exprlist, func, scalarvals, eval(D(G), P))
Definition: Evaluation of AggregateJoin
eval(D(G), AggregateJoin(A1, ..., An)) = AggregateJoin(eval(D(G), A1), ..., eval(D(G), An))
Note that if eval(D(G), Ai) is an error, it is ignored.
eval(D(G), Extend(P, var, expr)) = Extend(eval(D(G), P), var, expr)
For matching propery paths expressions, we write x:t
for term or variables, x
which is
of type t
or variable used for that type.
For example, var:term
means a variable used for RDF terms;
x:term
means x is some RDF term.
Definition: Node set of a graph
The node set of a graph G, nodes(G), is:
nodes(G) = { n | n is an RDF term that is used as a subject or object of a triple of G}
We define an auxillary function ALP used in the definitions of ZeroOrMorePath and OneOrMorePath. Note that the algorithm given here serves to specify the feature. An implementation is free to implement evaluation by any method that produces the same results for the query overall.
The matching algorithm is based on following all paths, and detecting when a graph node (subject or object), has been already visited on the path.
Informally, this algorithm attempts to extend the multiset of results by one application of path at each step, noting which nodes it has visited for this particular path in Visited. If a node has been visited for the path under consideration, it is not a candidate for another step. A node can still be visited multiple times if there are two different paths that visit it.
Definition: Function ALP
Let eval(x:term, path) be the evaluation of 'path', returning a multiset of RDF terms reached by path. ALP(x:term, path) = Let R = empty multiset ALP(x:term, path, R, {}) return is R # V is the set of nodes on this one path possibility. # R is the overall result. ALP(x:term, path, R:multiset of RDF terms , V:set of RDF terms) = if ( x in V ) return add x to V add x to R X = eval(x,path) For n:term in X ALP(n, path, R, V) End remove x from V
We now define the evalution of the path expression operations ZeroLengthPath, ZeroOrMorePath, OneOrMorePath and NegatedPropertySet.
Definition: Evaluation of ZeroLengthPath
eval(D(G), ZeroLengthPath(X, path, Y)
eval(D(G), ZeroLengthPath(vx:var, path, vy:var))) = { {(vx, term), (vy, term)} | term in nodes(G) } card[{(vx, term), (vy, term)}] = 1 eval(D(G), ZeroLengthPath(vx:var, path, y:term)) = { { (vx, y) } } card[{ (vx, y) }] = 1 eval(D(G), ZeroLengthPath(x:term, path, vy:var)) = { { (vy, x) } } card[{ (vy, x) }] = 1 eval(D(G), ZeroLengthPath(x:term, path, y:term)) = if x is the same term as y { {} } card[{}] = 1 else { } card[] = 0
Definition: Evaluation of ZeroOrMorePath
eval(D(G), ZeroOrMorePath(X, path, Y))
eval(D(G), ZeroOrMorePath(x:term, path, vy:var)) = { { (vy, n) } | n in ALP(x, path) } card[{(vy, n)}] = card[n] in ALP(x, path) eval(D(G), ZeroOrMorePath(vx:var, path, vy:var)) = { { (vx, t), (vy, n) } | t in nodes(G), (vy, n) in eval(D(G), ZeroOrMorePath(t, path, vy:var)) } card[{(vx, t), (vy, n)}] = card[n] in eval(D(G), ZeroOrMorePath(t, path, vy:var)) eval(D(G), ZeroOrMorePath(vx:var, path, y:term)) = eval(D(G), ZeroOrMorePath(y:term, ^path, vx:var)) eval(D(G), ZeroOrMorePath(x:term, path, y:term)) = { { } } if { (vy:var,y) } in eval(D(G), ZeroOrMorePath(x, path, vy); card[{ }] = 1 { } if y not in ALP(x, path), card[] = 0
Definition: Evaluation of OneOrMorePath
eval(D(G), OneOrMorePath(X, path, Y))
# For OneOrMorePath, we take one step of the path then start # recording nodes for results. eval(D(G), OneOrMorePath(x:term, path, vy:var)) = Let X = eval(x, path) Let R = the empty multiset For n in X ALP(n, path, R, {}) End result is R eval(D(G), OneOrMorePath(vx:var, path, vy:var)) = { { (vx, t), (vy, n) } | t in nodes(G), (vy, n) in eval(D(G), OneOrMorePath(t, path, vy:var)) } card[(vx, t), (vy, n)] = card[n] in eval(D(G), OneOrMorePath(t, path, vy:var)) eval(D(G), OneOrMorePath(vx:var, path, y:term)) = eval(D(G), OneOrMorePath(y:term, ^path, vx:var)) eval(D(G), OneOrMorePath(x:term, path, y:term)) = { { } } if { (vy:var, y) } in eval(D(G), OneOrMorePath(x, path, vy); card[{ }] = 1 { } if y not in ALP(x, path), card[] = 0
Definition: Evaluation of NegatedPropertySet
Write μ' as the extension of a solution mapping: μ'(μ,x) = μ(x) if x is a variable μ'(μ,t) = t if t is a RDF term
Let x and y be variables or RDF terms, and S a set of IRIs: eval(D(G), NPS(x, S, y)) = { μ | ∃ triple(μ'(μ,x), p, μ'(μ,y)) in G, such that the IRI of p ∉ S }
eval(D(G), ToList(P)) = ToList(eval(D(G), P))
eval(D(G), Distinct(L)) = Distinct(eval(D(G), L))
eval(D(G), Reduced(L)) = Reduced(eval(D(G), L))
eval(D(G), Project(L, vars)) = Project(eval(D(G), L), vars)
eval(D(G), OrderBy(L, condition)) = OrderBy(eval(D(G), L), condition)
eval(D(G), ToMultiSet(L)) = ToMultiSet(eval(D), M))
eval(D(G), Slice(L, start, length)) = Slice(eval(D(G), L), start, length)
The overall SPARQL design can be used for queries which assume a more elaborate form of entailment than simple entailment, by re-writing the matching conditions for basic graph patterns. Since it is an open research problem to state such conditions in a single general form which applies to all forms of entailment and optimally eliminates needless or inappropriate redundancy, this document only gives necessary conditions which any such solution should satisfy. These will need to be extended to full definitions for each particular case.
Basic graph patterns stand in the same relation to triple patterns that RDF graphs do to RDF triples, and much of the same terminology can be applied to them. In particular, two basic graph patterns are said to be equivalent if there is a bijection M between the terms of the triple patterns that maps blank nodes to blank nodes and maps variables, literals and IRIs to themselves, such that a triple ( s, p, o ) is in the first pattern if and only if the triple ( M(s), M(p), M(o) ) is in the second. This definition extends that for RDF graph equivalence to basic graph patterns by preserving variable names across equivalent patterns.
An entailment regime specifies
Detailed definitions for querying various entailment regimes can be found in SPARQL 1.1 Entailment Regimes.
Some entailment regimes can categorize some RDF graphs as inconsistent. For example, the RDF graph:
_:x rdf:type xsd:string . _:x rdf:type xsd:decimal .
is D-inconsistent when D contains the XSD datatypes. The effect of a query on an inconsistent graph is not covered by this specification, but must be specified by the particular SPARQL extension.
An entailment regime E must provide conditions on basic graph pattern
evaluation such that for any basic graph pattern BGP, any RDF graph G,
and any evaluation that satisfies the conditions, the resulting
multiset of solutions is uniquely determined up to RDF graph
equivalence. We denote the multiset of solutions from evaluating BGP
over G using E with Eval-E(G, BGP).
An entailment regime must further satisfy the following conditions:
SG E-entails (SG union μ1(BGP1) union ... union μn(BGPn))
These conditions do not fully determine the set of possible answers, since RDF allows unlimited amounts of redundancy. In addition, therefore, the following must hold.
(a) SG will often be graph equivalent to AG, but restricting this to E-equivalence allows some forms of normalization, for example elimination of semantic redundancies, to be applied to the source documents before querying.
(b) The construction in condition 3 ensures that any blank nodes introduced by the solution mapping are used in a way which is internally consistent with the way that blank nodes occur in SG. This ensures that blank node identifiers occur in more than one answer in an answer set only when the blank nodes so identified are indeed identical in SG. If the extension does not allow bindings to blank nodes, then this condition can be simplified to the condition:
SG E-entails μ(BGP) for each solution mapping μ.
(c) These conditions do not impose the SPARQL requirement that SG shares no blank nodes with AG or BGP. In particular, it allows SG to actually be AG. This allows query protocols in which blank node identifiers retain their meaning between the query and the source document, or across multiple queries. Such protocols are not supported by the current SPARQL protocol specification, however.
(d) Since conditions 1 to 3 are only necessary conditions on answers, condition 4 allows cases where the set of legal answers can be restricted in various ways.
(e) None of these conditions refer explicitly to instance mappings on blank nodes in BGP. For some entailment regimes, the existential interpretation of blank nodes cannot be fully captured by the existence of a single instance mapping. These conditions allow such regimes to give blank nodes in query patterns a 'fully existential' reading.
It is straightforward to show that SPARQL satisfies these conditions for the case where E is simple entailment, given that the SPARQL condition on SG is that it is graph-equivalent to AG but shares no blank nodes with AG or BGP (which satisfies the first condition). The only condition which is nontrivial is (3).
For every solution mapping μi, there is, by definition of basic graph pattern matching, an RDF instance mapping σi such that Pi(BGPi) is a subgraph of SG where Pi is the pattern instance mapping composed of μi and σi. Since BGPi and SG have no blank nodes in common, the ranges of σi and μi contain no blank nodes from BGPi; therefore, the solution mapping μi and the RDF instance mapping σi of Pi commute, so Pi(BGPi) = σi(μi(BGPi)). So
P1(BGP1) union ... union Pn(BGPn)
= σ1(μ1(BGP1)) union ... union
σn(μn(BGPn))
= [ σ1 + ... + σn](
μ1(BGP1) union ... union
μn(BGPn) )
since the domains of the σi RDF instance mappings are all mutually exclusive. Since they are also exclusive from SG,
SG union [ σ1 + ... + σn](
μ1(BGP1) union ... union μn(BGPn) )
= [ σ1 + ... + σn](SG union
μ1(BGP1) union ... union μn(BGPn) )
i.e.
SG union μ1(BGP1) union ... union μn(BGPn)
has an instance which is a subgraph of SG, so is simply entailed by SG by the RDF interpolation lemma [RDF-MT].
At-risk features
The SPARQL Working Group proposes to make the following changes to align SPARQL with the emerging Turtle specification.
~.-!$&'()*+,;=:/?#@%_
.
Feedback, both positive and negative, is invited by sending email to mailing list public-rdf-dawg-comments@w3.org, (public archive).
A SPARQL query string
is a Unicode character string (c.f. section 6.1 String concepts of [CHARMOD])
in the language defined by the following grammar, starting with the
Query production. For compatibility with future versions of
Unicode, the characters in this string may include Unicode codepoints that are unassigned
as of the date of this publication (see
Identifier
and Pattern Syntax [UNIID] section 4 Pattern Syntax). For
productions with excluded character classes (for example [^<>'{}|^`]
),
the characters are excluded from the range #x0 - #x10FFFF
.
A SPARQL Query String is processed for codepoint escape sequences before parsing by the grammar defined in EBNF below. The codepoint escape sequences for a SPARQL query string are:
Escape | Unicode code point |
---|---|
'\u' HEX HEX HEX HEX | A Unicode code point in the range U+0 to U+FFFF inclusive corresponding to the encoded hexadecimal value. |
'\U' HEX HEX HEX HEX HEX HEX HEX HEX | A Unicode code point in the range U+0 to U+10FFFF inclusive corresponding to the encoded hexadecimal value. |
where HEX is a hexadecimal character
HEX ::= [0-9] | [A-F] | [a-f]
Examples:
<ab\u00E9xy> # Codepoint 00E9 is Latin small e with acute - é \u03B1:a # Codepoint x03B1 is Greek small alpha - α a\u003Ab # a:b -- codepoint x3A is colon
Codepoint escape sequences can appear anywhere in the query string. They are
processed before parsing based on the grammar rules and so may be replaced by codepoints
with significance in the grammar, such as ":
" marking a prefixed name.
These escape sequences are not included in the grammar below. Only escape sequences
for characters that would be legal at that point in the grammar may be given. For
example, the variable "?x\u0020y
" is not legal (\u0020
is a space and is not permitted in a variable name).
White space (production WS
)
is used to separate two terminals which would otherwise be (mis-)recognized as one
terminal. Rule names below in capitals indicate where white space is significant;
these form a possible choice of terminals for constructing a SPARQL parser. White
space is significant in strings.
For example:
?a<?b&&?c>?d
is the token sequence variable '?a
', an IRI '<?b&&?c>
',
and variable '?d
', not a expression involving the operator '&&
'
connecting two expression using '<
' (less than) and '>
' (greater than).
Comments in SPARQL queries take the form of '#
', outside an IRI
or string, and continue to the end of line (marked by characters 0x0D
or 0x0A
) or end of file if there is no end of line after the comment
marker. Comments are treated as white space.
Text matched by the IRI_REF
production and PrefixedName
(after
prefix expansion) production, after escape processing, must conform to the generic
syntax of IRI references in section 2.2 of RFC 3987 "ABNF for IRI References and
IRIs" [RFC3987]. For example, the
IRI_REF
<abc#def>
may occur in a
SPARQL query string, but the IRI_REF
<abc##def>
must not.
Base IRIs declared with the BASE keyword must be absolute IRIs. A prefix declared with the PREFIX keyword may not be re-declared in the same query. See section 4.1.1, Syntax of IRI Terms, for a description of BASE and PREFIX.
The same blank node label may not be used in two separate basic graph patterns with a single query.
In addition to the codepoint escape sequences, the following escape sequences
any string
production (e.g.
STRING_LITERAL1
,
STRING_LITERAL2
,
STRING_LITERAL_LONG1
,
STRING_LITERAL_LONG2
):
Escape | Unicode code point |
---|---|
'\t' | U+0009 (tab) |
'\n' | U+000A (line feed) |
'\r' | U+000D (carriage return) |
'\b' | U+0008 (backspace) |
'\f' | U+000C (form feed) |
'\"' | U+0022 (quotation mark, double quote mark) |
"\'" | U+0027 (apostrophe-quote, single quote mark) |
'\\' | U+005C (backslash) |
Examples:
"abc\n" "xy\rz" 'xy\tz'
The EBNF notation used in the grammar is defined in Extensible Markup Language (XML) 1.1 [XML11] section 6 Notation.
Notes:
a
' which, in line with Turtle and N3, is used in place of the IRI
rdf:type
(in full,
http://www.w3.org/1999/02/22-rdf-syntax-ns#type
).QueryUnit
for SPARQL queries,
and UpdateUnit
for SPARQL Update requests.
AdditiveExpression
grammar rule
allows for this by covering the two cases of an expression followed by a
signed number. These produce an addition or subtraction of the unsigned
number as appropriate.INSERT DATA,
DELETE DATA,
DELETE WHERE
allow any amount of
whitespace between the words. The single space version is used in the grammar for clarity.
QuadData
and
QuadPattern
rules both use rule Quads
.
The rule QuadData
,
used in
INSERT DATA
and
DELETE DATA
,
must not allow variables in the quad patterns.
DELETE WHERE
,
DELETE
, nor in
DELETE DATA
.
BINDING
must be the
same as the number of each list of associated BindingValues
.
SELECT
clauses must only use
in-scope variables.
This only applies to expressions used on the left-hand side of AS
.
BIND
clause must not be already
in-scope.
Productions for terminals:
[129] | IRI_REF | ::= | '<' ([^<>"{}|^`\]-[#x00-#x20])* '>' |
[130] | PNAME_NS | ::= | PN_PREFIX? ':' |
[131] | PNAME_LN | ::= | PNAME_NS PN_LOCAL |
[132] | BLANK_NODE_LABEL | ::= | '_:' ( PN_CHARS_U | [0-9] ) ((PN_CHARS|'.')* PN_CHARS)? |
[133] | VAR1 | ::= | '?' VARNAME |
[134] | VAR2 | ::= | '$' VARNAME |
[135] | LANGTAG | ::= | '@' [a-zA-Z]+ ('-' [a-zA-Z0-9]+)* |
[136] | INTEGER | ::= | [0-9]+ |
[137] | DECIMAL | ::= | [0-9]* '.' [0-9]+ |
[138] | DOUBLE | ::= | [0-9]+ '.' [0-9]* EXPONENT | '.' ([0-9])+ EXPONENT | ([0-9])+ EXPONENT |
[139] | INTEGER_POSITIVE | ::= | '+' INTEGER |
[140] | DECIMAL_POSITIVE | ::= | '+' DECIMAL |
[141] | DOUBLE_POSITIVE | ::= | '+' DOUBLE |
[142] | INTEGER_NEGATIVE | ::= | '-' INTEGER |
[143] | DECIMAL_NEGATIVE | ::= | '-' DECIMAL |
[144] | DOUBLE_NEGATIVE | ::= | '-' DOUBLE |
[145] | EXPONENT | ::= | [eE] [+-]? [0-9]+ |
[146] | STRING_LITERAL1 | ::= | "'" ( ([^#x27#x5C#xA#xD]) | ECHAR )* "'" |
[147] | STRING_LITERAL2 | ::= | '"' ( ([^#x22#x5C#xA#xD]) | ECHAR )* '"' |
[148] | STRING_LITERAL_LONG1 | ::= | "'''" ( ( "'" | "''" )? ( [^'\] | ECHAR ) )* "'''" |
[149] | STRING_LITERAL_LONG2 | ::= | '"""' ( ( '"' | '""' )? ( [^"\] | ECHAR ) )* '"""' |
[150] | ECHAR | ::= | '\' [tbnrf\"'] |
[151] | NIL | ::= | '(' WS* ')' |
[152] | WS | ::= | #x20 | #x9 | #xD | #xA |
[153] | ANON | ::= | '[' WS* ']' |
[154] | PN_CHARS_BASE | ::= | [A-Z] | [a-z] | [#x00C0-#x00D6] | [#x00D8-#x00F6] | [#x00F8-#x02FF] | [#x0370-#x037D] | [#x037F-#x1FFF] | [#x200C-#x200D] | [#x2070-#x218F] | [#x2C00-#x2FEF] | [#x3001-#xD7FF] | [#xF900-#xFDCF] | [#xFDF0-#xFFFD] | [#x10000-#xEFFFF] |
[155] | PN_CHARS_U | ::= | PN_CHARS_BASE | '_' |
[156] | VARNAME | ::= | ( PN_CHARS_U | [0-9] ) ( PN_CHARS_U | [0-9] | #x00B7 | [#x0300-#x036F] | [#x203F-#x2040] )* |
[157] | PN_CHARS | ::= | PN_CHARS_U | '-' | [0-9] | #x00B7 | [#x0300-#x036F] | [#x203F-#x2040] |
[158] | PN_PREFIX | ::= | PN_CHARS_BASE ((PN_CHARS|'.')* PN_CHARS)? |
[159] | PN_LOCAL | ::= | (PN_CHARS_U | [0-9] | PLX ) ( ( PN_CHARS | '.' | PLX )* ( PN_CHARS | PLX ) ) ? > |
[160] | PLX | ::= | PERCENT | PN_LOCAL_ESC |
[161] | PERCENT | ::= | '%' HEX HEX |
[162] | HEX | ::= | [0-9] | [A-F] | [a-f] |
[163] | PN_LOCAL_ESC | ::= | '\' ( '_' | '~' | '.' | '-' | '!' | '$' | '&' | "'" | '(' | ')' | '*' | '+' | ',' | ';' | '=' | ':' | '/' | '?' | '#' | '@' | '%' ) |
See Section 19 SPARQL Grammar regarding conformance of SPARQL Query strings, and section 16 Query Forms for conformance of query results. See section 22. Internet Media Type for conformance to the application/sparql-query media type.
This specification is intended for use in conjunction with the SPARQL Protocol [SPROT], the SPARQL Query Results XML Format [SPARQL XML Results] and the SPARQL Query Results JSON Format [SPARQL JSON Results]. See those specifications for their conformance criteria.
Note that the SPARQL protocol describes a means for conveying SPARQL queries to an SPARQL query processing service and returning the query results to the entity that requested them.
SPARQL queries using FROM, FROM NAMED, or GRAPH may cause the specified URI to
be dereferenced. This may cause additional use of network, disk or CPU resources
along with associated secondary issues such as denial of service. The security issues
of Uniform Resource Identifier
(URI): Generic Syntax [RFC3986] Section 7 should be considered.
In addition, the contents of file:
URIs can in some cases be accessed,
processed and returned as results, providing unintended access to local resources.
SPARQL requests may cause additional requests to be issued from the SPARQL endpoint, such as FROM NAMED. The endpoint is potentially within an organisations firewall or DMZ, and so such queries may be a source of indirection attacks.
The SPARQL language permits extensions, which will have their own security implications.
Multiple IRIs may have the same appearance. Characters in different scripts may look similar (a Cyrillic "о" may appear similar to a Latin "o"). A character followed by combining characters may have the same visual representation as another character (LATIN SMALL LETTER E followed by COMBINING ACUTE ACCENT has the same visual representation as LATIN SMALL LETTER E WITH ACUTE). Users of SPARQL must take care to construct queries with IRIs that match the IRIs in the data. Further information about matching of similar characters can be found in Unicode Security Considerations [UNISEC] and Internationalized Resource Identifiers (IRIs) [RFC3987] Section 8.
The Internet Media Type / MIME Type for the SPARQL Query Language is "application/sparql-query".
It is recommended that sparql query files have the extension ".rq" (lowercase) on all platforms.
It is recommended that sparql query files stored on Macintosh HFS file systems be given a file type of "TEXT".