Copyright © 2006 W3C® ( MIT, ERCIM, Keio), All Rights Reserved. W3C liability, trademark, and document use rules apply.
RDF is a flexible and extensible way to represent information about World Wide Web resources. It is used to represent, among other things, personal information, social networks, metadata about digital artifacts, as well as provide a means of integration over disparate sources of information. A standardized query language for RDF data with multiple implementations offers developers and end users a way to write and to consume the results of queries across this wide range of information. Used with a common protocol, applications can access and combine information from across the Web.
This document describes the query language part of the SPARQL Protocol And RDF Query Language for easy access to RDF stores. It is designed to meet the requirements and design objectives described in RDF Data Access Use Cases and Requirements [UCNR. The SPARQL query language consists of the syntax and semantics for asking and answering queries against RDF graphs. SPARQL contains capabilities for querying by triple patterns, conjunctions, disjunctions, and optional patterns. It also supports constraining queries by source RDF graph and extensible value testing. Results of SPARQL queries can be ordered, limited and offset in number, and presented in several different forms.
@@Revise when rest finished.
This is a live document and is subject to change without notice. It reflects the best effort of the editors to reflect implementation experience and incorporate input from various members of the WG, but is not yet endorsed by the WG as a whole.
The change log enumerates changes since the Candidate Recommendation of 6 April 2006. We have been tracking threads in the public-rdf-dawg-comments archive more closely. A status report is updated every week or so.
For the definitions, we have an XSLT transformation, defns.xsl, that extracts them from this document. A live version of the output is available via the W3C XSLT service.
See also: SPARQL Test Cases, in progress.
In addition, the collected formal definitions are collected into a single document "SPARQL Query Language for RDF - Formal Definitions".
@@Scope of blank nodes in BGP 5.4 + clarify the group example of { {} {} }
@@Consider putting formal definitions first for OPTIONAL, UNION and result forms (10.2, 10.3, 10.4, 10.5)
@@ Grammar extracts maybe out of line with the grammar while the grammar is revised for clarity.
An RDF graph is a set of triples; each triple consists of a subject, a predicate and an object. RDF graphs are defined in RDF Concepts and Abstract Syntax [CONCEPTS]. These triples can come from a variety of sources. For instance, they may come directly from an RDF document; they may be inferred from other RDF triples; or they may be the RDF expression of data stored in other formats, such as XML or relational databases. The RDF graph may be virtual, in that it is not fully materialized, only doing the work needed for each query to execute.
SPARQL is a query language for getting information from such RDF graphs. It provides facilities to:
As a data access language, it is suitable for both local and remote use. The companion SPARQL Protocol for RDF document [SPROT] describes the remote access protocol.
This document defines the SPARQL, an RDF query language.
@@About grammar extracts
@@ This text does somewhere:
Later sections of this document describe how other graph
patterns can be built using the graph operators OPTIONAL
and UNION
; how graph patterns can be
grouped together; how queries can
extract information from more than one
graph, and how it is also possible to restrict the values allowed in
matching a pattern.
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# |
@@ Need a bit more, esp blank nodes.
The data format used in this document is Turtle [TURTLE], used to show each triple explicitly. Turtle allows URIs to be abbreviated with prefixes:
@prefix dc: <http://purl.org/dc/elements/1.1/> . @prefix : <http://example.org/book/> . :book1 dc:title "SPARQL Tutorial" .
Results in the form of result sets are illustrated results in tabular form.
x | y | z |
---|---|---|
"Alice" | <http://example/a> |
The term "binding" is used as a descriptive term to refer to a
pair (variable, RDF term). In this result set, there are variables x
,
y
and z
(shown as column hearers). Each solution is
shown as a row in the body of the table. Here, there is a single
solution, where 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, for example, optional matches and alternative matches may leave some variables unbound in
some rows.
Results can be returned in XML using the SPARQL Query Results XML Format [RESULTS].
The SPARQL query language is based on matching graph patterns. The simplest graph pattern is the triple pattern, which is like an RDF triple, but with the possibility of a query variable instead of an RDF term in the subject, predicate or object positions. Combining triple patterns gives a basic graph pattern, where an exact match to a graph is needed to fulfill a pattern.
This section gives an introduction to the basic matching features of SPARQL.
The example below shows a SPARQL query to find the title of a
book from the information in the given RDF graph. The query
consists of two parts, the SELECT
clause and the
WHERE
clause. The SELECT
clause
identifies the variables to appear in the query results, and the
WHERE
clause has one triple pattern.
Data:
<http://example.org/book/book1> <http://purl.org/dc/elements/1.1/title> "SPARQL Tutorial" .
Query:
SELECT ?title WHERE { <http://example.org/book/book1> <http://purl.org/dc/elements/1.1/title> ?title . }
This query, on the data above has one solution:
Query Result:
title |
---|
"SPARQL Tutorial" |
The results of a query is a sequence of solutions, giving the ways in which the query pattern matches the data. The sequence of solutions is further modified by the solution sequence modifiers. 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> .
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> |
The results enumerate the RDF terms to which the selected variables can be bound in the query pattern in order to match triples in the data. 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, and all the named variables used in the query pattern must be bound in every solution.
The data below contains a number of 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 "42"^^xsd:integer .
:y ns:p "abc"^^dt:specialDatatype .
:z ns:p "cat"@en .
This RDF data is the target for query examples in the following sections.
The pattern in the following query has a solution
with variable v
bound to :x
because 42
is syntax for
"42"^^<http://www.w3.org/2001/XMLSchema#integer>
.
SELECT ?v WHERE { ?v ?p 42 }
v |
---|
<http://example.org/ns#x> |
The following query has a solution with variable
v
bound to :y
. The query processor does
not have to have any understanding of the values in the space
of the datatype because, in this case, lexical form and
datatype IRI both match exactly.
SELECT ?v WHERE { ?v ?p "abc"^^<http://example.org/datatype#specialDatatype> }
v |
---|
<http://example.org/ns#y> |
This following query has no solution because
"cat"
is not the same RDF literal as
"cat"@en
:
SELECT ?x WHERE { ?x ?p "cat" }
x |
---|
but this does find a solution where variable x
is bound to :z
:
SELECT ?x WHERE { ?x ?p "cat"@en }
x |
---|
<http://example.org/ns#z> |
because "cat"@en
is a term in the graph whereas
"cat"
is not.
Graph pattern matching creates bindings of variables. It is possible to further restrict solutions by constraining the RDF terms that can be used as bindings of variables. Value constraints take the form of boolean-valued expressions; the language also allows application-specific constraints on the values in a solution.
@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 .
Variable bindings can be restricted to strings matching a regular
expression by using the regex
operator. Only plain literals with no language tag and XSD
strings are matched by regex
. regex
can be used to
match the lexical forms of other literals by using the
str operator.
Query:
PREFIX dc: <http://purl.org/dc/elements/1.1/> SELECT ?title WHERE { ?x dc:title ?title FILTER regex(?title, "SPARQL") }
Query Result:
title |
---|
"SPARQL Tutorial" |
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:
title |
---|
"The Semantic Web" |
It is also possible to restrict the values of literals that have number values. Filters apply to the value of the literal, not its lexical form.
Query:
PREFIX dc: <http://purl.org/dc/elements/1.1/> PREFIX ns: <http://example.org/ns#> SELECT ?title ?price WHERE { ?x ns:price ?price . FILTER (?price < 30.5) . ?x dc:title ?title . }
Query Result:
title | price |
---|---|
"The Semantic Web" | 23 |
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.
@@ isURI/isLiteral/isBlank. Discuss these test
RDF defines a reification vocabulary which provides for describing RDF statements without stating them. These descriptions of statements can be queried by using the defined vocabulary. SPARQL does not treat querying reified data differently from any other RDF data. SPARQL can be used to query graph-pattern matches using the reification vocabulary.
@prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> . @prefix dc: <http://purl.org/dc/elements/1.1/> . @prefix : <http://example/ns#> . _:a rdf:subject <http://example.org/book/book1> . _:a rdf:predicate dc:title . _:a rdf:object "SPARQL" . _:a :saidBy "Alice" . _:b rdf:subject <http://example.org/book/book1> . _:b rdf:predicate dc:title . _:b rdf:object "SPARQL Tutorial" . _:b :saidBy "Bob" .
In this example data, there is no RDF triple giving the title of the book; there are triples that describe two such RDF statements but the statements themselves are not asserted in the graph. A query asking for any titles of any book returns nothing.
PREFIX dc: <http://purl.org/dc/elements/1.1/> SELECT ?book ?title WHERE { ?book dc:title ?title }
Query Result:
book | title |
---|
There are no triples in the graph with dc:title
in the property position (it appears in the object position in
the data).
A query can ask about descriptions of statements made by "Bob":
PREFIX rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> PREFIX dc: <http://purl.org/dc/elements/1.1/> PREFIX : <http://example/ns#> SELECT ?book ?title WHERE { ?t rdf:subject ?book . ?t rdf:predicate dc:title . ?t rdf:object ?title . ?t :saidBy "Bob" . }
and there is one such description for a statement made by Bob:
book | title |
---|---|
<http://example.org/book/book1> | "SPARQL Tutorial" |
@@ Move to section 10
The presence of blank nodes in query results can be indicated by labels in the serialization of query results.
Blank nodes labels are local to the result set of a query. An application
or client cannot usefully use blank node labels to formulate a query that
directly refers to a particular blank node. In
effect, this means that information about co-occurrences of blank
nodes may be treated as scoped to the results as defined in
"SPARQL Query Results
XML Format" or the CONSTRUCT
result form.
@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 }
x | name |
---|---|
_:c | "Alice" |
_:d | "Bob" |
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 were the same or different.
x | name |
---|---|
_:r | "Alice" |
_:s | "Bob" |
These two results have the same information: the blank nodes
used to match the query are different in the two solutions. There
would be no relation if the label _:a
were used in
the results and the blank node label in the data graph.
This section covers the syntax used by SPARQL for RDF terms and triple patterns. The full grammar is given in appendix A.
The terms delimited by "<>
" are IRI
references [RFC3987]; the delimiters do not form part
of the reference. They stand for IRIs,
either directly, or relative to a base IRI. IRIs are a
generalization of URIs [RFC3986] and are
fully compatible with URIs and URLs.
The SPARQL syntax provides two abbreviation mechanisms for IRIs, prefixed names and relative IRIs.
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 ":
". It is mapped to an IRI by
concatenating the local part to the IRI corresponding to the
prefix. The prefix label may be the empty string.
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
quotes, 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 and are
interpreted as typed literals of datatype
xsd:integer
; decimal numbers, where there is '.' in
the number but no exponent, are interpreted as
xsd:decimal
and a number with an exponent is
interpreted as an 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
1.0e6
, 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
[60] |
RDFLiteral |
::= | String
( LANGTAG | ( '^^' IRIref )
)? |
[61] |
NumericLiteral |
::= | INTEGER | DECIMAL
| DOUBLE |
[62] |
BooleanLiteral |
::= | 'true' | 'false' |
[63] |
String |
::= | STRING_LITERAL1 | STRING_LITERAL2 | STRING_LITERAL_LONG1 |
STRING_LITERAL_LONG2 |
[73] |
LANGTAG |
::= | '@' [a-zA-Z]+ ('-'
[a-zA-Z0-9]+)* |
[74] |
INTEGER |
::= | [0-9]+ |
[75] |
DECIMAL |
::= | [0-9]+ '.' [0-9]* | '.'
[0-9]+ |
[76] |
DOUBLE |
::= | [0-9]+ '.' [0-9]* EXPONENT | '.' ([0-9])+ EXPONENT | ([0-9])+ EXPONENT |
[77] |
EXPONENT |
::= | [eE] [+-]? [0-9]+ |
[78] |
STRING_LITERAL1 |
::= | "'" ( ([^#x27#x5C#xA#xD]) |
ECHAR
)* "'" |
[79] |
STRING_LITERAL2 |
::= | '"' ( ([^#x22#x5C#xA#xD]) |
ECHAR
)* '"' |
[80] |
STRING_LITERAL_LONG1 |
::= | "'''" ( ( "'" | "''" )? (
[^'\] | ECHAR ) )* "'''" |
[81] |
STRING_LITERAL_LONG2 |
::= | '"""' ( ( '"' | '""' )? (
[^"\] | ECHAR ) )* '"""' |
Query variables in SPARQL queries have global scope; use of a given
variable name anywhere in a query identifies the same variable. Variables
are indicated by "?"; the "?" does not form part of the variable
name. "$" is an alternative to "?". In a query, $abc
and ?abc
are the same variable. The possible names for variables are given in the
SPARQL grammar.
@@Talk about identifiers as mere syntax elements
@@revise/rework when section 5 (BGP matching) updated
A blank
node can appear in a query pattern and will take part in the
pattern matching. Blank nodes are indicated by either the label form
"_:a" or by use of "[ ]". A blank node that is used in only one place in the query
syntax can be abbreviated with []
. A unique blank
node will be created and used to form the triple pattern. Blank node labels
are written as "_:a
" for a blank node with label
"a
" and the label is scoped to the basic graph pattern.
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" .
is equivalent to the two triples:
_:b57 :p "v" . _:b57 :q "w" .
and as an object:
:x :q [ :p "v" ] .
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 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:
_:b18 foaf:name ?name . _:b18 foaf:mbox <mailto:alice@example.org> .
@@ Add rules for [:p "object] when grammar stable again.
[66] |
BlankNode |
::= | BLANK_NODE_LABEL | ANON |
[70] |
BLANK_NODE_LABEL |
::= | '_:' NCNAME |
[87] |
ANON |
::= | '[' WS*
']' |
Triple Patterns are written as a list of subject, predicate, 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 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, then
these can be written using the ",
" notation.
?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_" .
giving:
?x foaf:name ?name . ?x foaf:nick "Alice" . ?x foaf:nick "Alice_" .
RDF
collections can be written in triple patterns using the
syntax "( )". 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 and blank nodes are allocated for the
collection and the blank node at the head of the collection can
be used as a subject or object in other triple patterns. Blank nodes allocated
do not occur else in the query.
(1 ?x 3 4) :p "w" .
is a short form for (the blank node labels 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 a short form 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 short for:
?x rdf:type :Class1 . _:b0 rdf:type :appClass . _:b0 :p "v" .
where rdf
: is the prefix for
http://www.w3.org/1999/02/22-rdf-syntax-ns#
The following terms are used from RDF Concepts and Abstract Syntax [CONCEPTS]
SPARQL is defined in terms of IRIs. RDF Concepts and Abstract Syntax "anticipates an RFC on Internationalized Resource Identifiers. Implementations may issue warnings concerning the use of RDF URI References that do not conform with [IRI draft] or its successors."
SPARQL is defined in terms of IRIs, a subset of RDF URI References that omits 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 union RDF-L union 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.
Note that all IRIs 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.
SPARQL query results are a binding of query variables to RDF Terms.
A query variable is a member of the set V where V is infinite and disjoint from RDF-T.
The building blocks of queries are triple patterns.
A triple pattern is member
of the set:
(RDF-T union V) x (I union V) x (RDF-T union 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.
[32] |
TriplesSameSubject |
::= | VarOrTerm PropertyListNotEmpty |
TriplesNode PropertyList |
[33] |
PropertyList |
::= | PropertyListNotEmpty? |
[34] |
PropertyListNotEmpty |
::= | Verb
ObjectList ( ';' PropertyList )? |
[35] |
ObjectList |
::= | GraphNode ( ',' ObjectList
)? |
[36] |
Verb |
::= | VarOrIRIref | 'a' |
SPARQL queries are made of one or more graph patterns. Graph patterns can be combined into larger patterns.
A Graph Pattern is one of:
Formally, a SPARQL query contains four components: the pattern, the dataset being queried, solution modifiers, and the result form.
A SPARQL query is a tuple (GP, DS, SM, R) where:
The graph pattern of a query is called the query pattern.
The graph pattern may be the empty pattern. The set of solution modifiers may be the empty set.
A variable substitution is a substitution function from a subset of V, the set of variables, to the set of RDF terms, RDF-T.
A pattern solution, S, is a variable substitution whose domain includes all the variables in V and whose range is a subset of the set of RDF terms.
The result of replacing every member v of V in a graph pattern P by S(v) is written S(P).
If v is not in the domain of S then S(v) is defined to be v.
The term "solution" is used for "pattern solution" where it is unambiguous.
@@ Consider whether to have a "RDF dataset" section in "Initial Definitions"
Graph patterns match against the default graph of an RDF dataset, except for the RDF Dataset Graph Pattern. In this section, all matching is described for a single graph, being the default graph of the RDF dataset being queried.
Definition: Value Constraint
A value constraint is a boolean-valued expression of variables and RDF Terms.
For value constraint C, a solution S matches C if S(C) is true, where S(C) is the boolean-valued expression obtained by substitution of the variables mentioned in C.
Constraints may be restrictions on the value associated with an RDF Term or they may be restrictions on some part of an RDF term, such as its lexical form. There is a set of functions & operators in SPARQL for constraints. In addition, there is an extension mechanism to provide access to functions that are not defined in the SPARQL language. Restrictions on the value of a RDF term are based on its value, as given by any datatype; value tests only apply to RDF literals.
A constraint may lead to an error condition when testing some RDF term. The exact error will depend on the constraint: for example, in numeric operations, solutions with variables bound to a non-number or a blank node will lead to an error. Any potential solution that causes an error condition in a constraint will not form part of the final results, but does not cause the query to fail.
@@Filters apply to the whole of the group they are in. Canonically, all matchingis done, then filters are applied. Implementations wil optimize this.
[27] |
Constraint |
::= | 'FILTER' ( BrackettedExpression |
BuiltInCall | FunctionCall ) |
A basic graph pattern is a set of triple patterns and forms the basis of SPARQL query matching. Matching a basic graph pattern is defined in terms of generic entailment to allow for future extension of the language.
A Basic Graph Pattern is a set of Triple Patterns.
An E-entailment regime is a binary relation between subsets of RDF graphs.
A graph in the range of an E-entailment is called well-formed for the E-entailment.
This specification covers only simple entailment [RDF-MT] as E-entailment. Examples of other E-entailment regimes are RDF entailment [RDF-MT], RDFS entailment [RDF-MT], OWL entailment [OWL-Semantics].
Logical entailment may result in inconsistent RDF graphs. For example, "-1"^^xsd:positiveInteger is inconsistent with respect to D-entailment [RDF-MT]. The effect of any query on an inconsistent graph is not covered by this specification.
Two basic graph patterns are 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 graphs.
@@ Better name: "General Basic Graph Pattern Matching" ??
A Scoping Set B is some set of RDF terms.
The scoping set restricts the values of variable assignments in a solution. The scoping set may be characterized differently by different entailment regimes.
The Scoping Graph G' for RDF graph G, is an RDF Graph that is graph-equivalent to G
The scoping graph makes the graph to be matched independent of the chosen blank node names.
The same scoping set and scoping graph is used for all basic graph pattern matching in a single SPARQL query request.
Given an entailment regime E, a basic graph pattern BGP, and RDF graph G, with scoping graph G', then BGP E-matches with pattern solution S on graph G with respect to scoping set B if:
The introduction of the basic graph pattern BGP' in the above definition makes the query basic graph pattern independent of the choice of blank node names in the basic graph pattern.
These definitions allow for future extensions to SPARQL. This document defines SPARQL for simple entailment and the scoping set B is the set of all RDF terms in G'.
When using simple entailment, the operation of querying an RDF graph provides access to the graph structure, up to blank node renaming; nothing that is not already in the graph G needs to be inferred or constructed, even implicitly.
A pattern solution can then be defined as follows: to match a basic graph pattern under simple entailment, it is possible to proceed by finding a mapping from blank nodes and variables in the basic graph pattern to terms in the graph being matched; a pattern solution is then a mapping restricted to just the variables, possibly with blank nodes renamed. Moreover, a uniqueness property guarantees the interoperability between SPARQL systems: given a graph and a basic graph pattern, the set of all the pattern solutions is unique up to blank node renaming.
As an example of a Basic Graph Pattern:
Data:
@prefix foaf: <http://xmlns.com/foaf/0.1/> . _:a foaf:name "Johnny Lee Outlaw" . _:a foaf:mbox <mailto:outlaw@example.com> . _:b foaf:name "A. N. Other" . _:b foaf:mbox <mailto:other@example.com> .
There is a blank node [CONCEPTS] in
this dataset, identified by _:a
. The label is only
used within the file for encoding purposes. The label
information is not in the RDF graph.
Query:
PREFIX foaf: <http://xmlns.com/foaf/0.1/> SELECT ?mbox WHERE { ?x foaf:name "Johnny Lee Outlaw" . ?x foaf:mbox ?mbox }
Query Result:
mbox |
---|
<mailto:outlaw@example.com> |
This query contains a basic graph pattern of two triple
patterns, each of which must match with the same solution for the
graph pattern to match. The pattern solution matching the basic
graph pattern maps the variable 'x'
to blank node
_:a
and variable 'mbox'
to the IRI
mailto:outlaw@example.com
. The query only returns
the variable 'mbox'
.
@@ Is a split BGP still a single BGP?
In the SPARQL syntax, Basic Graph Patterns are sequences of triple patterns. Other graph patterns separate basic patterns. The two query fragments below each contain the same basic graph pattern of
{ _:x :p ?v . _:x :q ?w . }
with the scope of the blank node label being the basic graph pattern.
{ _:x :p ?v . FILTER (?v < 3) . _:x :q ?w . }
{ _:x :p ?v . _:x :q ?w . FILTER (?v < 3) . }
@@ Don't need this summary any more ?
Complex graph patterns can be made by combining simpler graph patterns. The ways of creating graph patterns are:
Definition: Group Graph Pattern
A group graph pattern GGP is a set of graph patterns, GPi.
A solution of Group Graph Pattern GGP on graph G is any solution S such that, for every element GPi of GGP, S is a solution of GPi.
For any solution, the same variable is given the same value everywhere in the set of graph patterns making up the group graph pattern.
In a SPARQL query string, a group graph pattern is delimited
with braces: {}
. For example, this query has a group graph
pattern of one basic graph pattern as the query 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 . } }
[19] |
GroupGraphPattern |
::= | '{' GraphPattern '}' |
The group pattern:
{ }
matches any graph (including the empty graph) requiring no substitutions for variables.
SELECT ?x WHERE {}
matches with one solution which has no substitutions for variables.
@@ More? Need to couple to a pattern solution involves the "required" terms.
There is no implied order of graph patterns within a Group Graph Pattern. Any solution for the group graph pattern that can satisfy all the graph patterns in the group is valid, independently of the order that may be implied by the lexical order of the graph patterns in the group.
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 the query, every variable is bound to an RDF Term in a pattern solution. However, regular, complete structures cannot be assumed in all RDF graphs and it is useful to be able to have queries that allow information to be added to the solution where the information is available, but not to have the solution rejected because some part of the query pattern does not match. Optional matching provides this facility; if the optional part does not lead to any solutions, it creates no bindings.
Optional parts of the graph pattern may be specified syntactically with the OPTIONAL keyword applied to a graph pattern:
pattern OPTIONAL { pattern }
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" .
PREFIX foaf: <http://xmlns.com/foaf/0.1/> SELECT ?name ?mbox WHERE { ?x foaf:name ?name . OPTIONAL { ?x foaf:mbox ?mbox } }
With the data above, the query result is:
name | mbox |
---|---|
"Alice" | <mailto:alice@example.com> |
"Alice" | <mailto:alice@work.example> |
"Bob" |
There is no value of mbox
in the solution where
the name is "Bob"
. It is unbound.
This query finds the names of people in the data. If there is
a triple with predicate mbox
and same subject, a
solution will contain the object of that triple as well. In the
example, only a single triple pattern is given in the optional
match part of the query but, in general, it is any graph pattern.
The whole graph pattern of an optional graph pattern must match
for the optional graph pattern to affect the query solution.
Constraints can be given in an optional graph pattern as this example shows:
@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 .
PREFIX dc: <http://purl.org/dc/elements/1.1/> PREFIX ns: <http://example.org/ns#> SELECT ?title ?price WHERE { ?x dc:title ?title . OPTIONAL { ?x ns:price ?price . FILTER (?price < 30) } }
title | price |
---|---|
"SPARQL Tutorial" | |
"The Semantic Web" | 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.
Data:
@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> .
Query:
PREFIX foaf: <http://xmlns.com/foaf/0.1/> SELECT ?name ?mbox ?hpage WHERE { ?x foaf:name ?name . OPTIONAL { ?x foaf:mbox ?mbox } . OPTIONAL { ?x foaf:homepage ?hpage } }
Query result:
name | mbox | hpage |
---|---|---|
"Alice" | <http://work.example.org/alice/> | |
"Bob" | <mailto:bob@work.example> |
In an optional match, either an additional graph pattern matches a graph, thereby defining one or more pattern solutions; or it passes the solution without adding any additional bindings.
An optional graph pattern is a combination of a pair of graph patterns. The second pattern modifies pattern solutions of the first pattern but does not fail matching of the overall optional graph pattern.
If Opt(A, B) is an optional graph pattern, where A and B are graph patterns, then S is a solution of optional graph pattern if S is a pattern solution of A and of B otherwise if S is a solution to A, but not to A and B.
The syntactic form:
{ OPTIONAL { pattern } }
is defined to be
{ { } OPTIONAL { pattern } }
[24] |
OptionalGraphPattern |
::= | 'OPTIONAL' GroupGraphPattern |
The OPTIONAL
keyword is left-associative :
pattern OPTIONAL { pattern } OPTIONAL { pattern }
matches the same as:
{ pattern OPTIONAL { pattern } } OPTIONAL { pattern }
Optional patterns can occur inside any group graph pattern, including a group graph pattern which itself is optional, forming a nested pattern. The outer optional graph pattern must match for any nested optional pattern to be matched.
Data:
@prefix foaf: <http://xmlns.com/foaf/0.1/> . @prefix vcard: <http://www.w3.org/2001/vcard-rdf/3.0#> . _:a foaf:name "Alice" . _:a foaf:mbox <mailto:alice@work.example> . _:a vcard:N _:x . _:x vcard:Family "Hacker" . _:x vcard:Given "Alice" . _:b foaf:name "Bob" . _:b foaf:mbox <mailto:bob@work.example> . _:b foaf:N _:z . _:z vcard:Family "Hacker" . _:e foaf:name "Ella" . _:e vcard:N _:y . _:y vcard:Given "Eleanor" .
Query:
PREFIX foaf: <http://xmlns.com/foaf/0.1/> PREFIX vcard: <http://www.w3.org/2001/vcard-rdf/3.0#> SELECT ?foafName ?mbox ?gname ?fname WHERE { ?x foaf:name ?foafName . OPTIONAL { ?x foaf:mbox ?mbox } . OPTIONAL { ?x vcard:N ?vc . ?vc vcard:Given ?gname . OPTIONAL { ?vc vcard:Family ?fname } } }
Query result:
foafName | mbox | gname | fname |
---|---|---|---|
"Alice" | <mailto:alice@work.example> | "Alice" | "Hacker" |
"Bob" | <mailto:bob@work.example> | ||
"Ella" | "Eleanor" |
This query finds the name, optionally the mbox, and also the vCard given name; further, if there is a vCard Family name as well as the Given name, the query finds that as well.
By nesting the optional pattern involving
vcard:Family,
the query only matches these if there
are appropriate vcard:N
and vcard:Given
triples in the data. Here the expression is a simple triple
pattern on vcard:N
but it could be a complex graph
pattern with value constraints.
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.
The UNION
keyword is the syntax for pattern
alternatives.
Data:
@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)" .
Query:
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:
title |
---|
"SPARQL Protocol Tutorial" |
"SPARQL" |
"SPARQL (updated)" |
"SPARQL Query Language Tutorial" |
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. If the application wishes to know how exactly the information was recorded, then the query:
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 } }
x | y |
---|---|
"SPARQL (updated)" | |
"SPARQL Protocol Tutorial" | |
"SPARQL" | |
"SPARQL Query Language Tutorial" |
will return results with the variables x
or
y
bound depending on which way the query processor
matches the pattern to the data. Note that, unlike an
OPTIONAL
pattern, if neither part of the
UNION
pattern matched, then the graph pattern
would not match.
The UNION
operator combines graph patterns, so
more than one triple pattern can be given in each alternative
possibility:
PREFIX dc10: <http://purl.org/dc/elements/1.1/> PREFIX dc11: <http://purl.org/dc/elements/1.0/> SELECT ?title ?author WHERE { { ?book dc10:title ?title . ?book dc10:creator ?author } UNION { ?book dc11:title ?title . ?book dc11:creator ?author } }
author | title |
---|---|
"Alice" | "SPARQL Protocol Tutorial" |
"Bob" | "SPARQL Query Language Tutorial" |
This query will only match a book if it has both a title and creator predicate from the same version of Dublin Core.
Definition: Union Graph Pattern
A union graph pattern is a set of graph patterns GPi.
A union graph pattern matches a graph G with solution S if there is some GPi such that GPi matches G with solution S.
Query results involving a pattern containing GP1 and GP2 will include separate solutions for each match where GP1 and GP2 give rise to different sets of bindings.
[26] |
GroupOrUnionGraphPattern |
::= | GroupGraphPattern (
'UNION' GroupGraphPattern
)* |
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, each identified by IRI. A SPARQL query can match different parts of the query pattern against different graphs as described in the query section.
Definition: RDF Dataset
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.
There may be no named graphs; there is always a default graph.
In the previous sections, all queries have been shown executed against a single graph, being the default graph of an RDF dataset. A query does not need to involve the default graph; the query can just involve matching named graphs.
The definition of RDF Dataset does not restrict the relationships of named and default graphs. Information can be repeated in different graphs; relationships between graph can exposed. Two useful arrangements are:
Example 1:
# 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 arranegment of graphs in an RDF Dataset is to have the default graph being 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 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.
A query processor may use these IRIs in any way to associate an RDF Dataset with a query. For example, it could use IRIs to retrieve documents, parse them and use the resulting triples as one of the graphs; alternatively, it might only service queries that specify IRIs of graphs that it has already stored.
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
clausesFROM
NAMED
clause.[9] |
DatasetClause |
::= | 'FROM' ( DefaultGraphClause | NamedGraphClause ) |
[10] |
DefaultGraphClause |
::= | SourceSelector |
[11] |
NamedGraphClause |
::= | 'NAMED' SourceSelector |
[12] |
SourceSelector |
::= | IRIref |
[26] |
GroupOrUnionGraphPattern |
::= | GroupGraphPattern (
'UNION' GroupGraphPattern
)* |
Each FROM
clause contains an IRI that indicates
the graph to be used to form the default graph. This does not put
the graph in as a named graph; a query can do this by also
specifying the graph in the FROM NAMED
clause.
In this example, there is a single default graph:
# Default graph (stored 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> .
PREFIX foaf: <http://xmlns.com/foaf/0.1/> SELECT ?name FROM <http://example.org/foaf/aliceFoaf> WHERE { ?x foaf:name ?name }
name |
---|
"Alice" |
If a query provides more than one FROM
clause,
providing more than one IRI to indicate the default graph, then
the default graph is based on 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 actually the relationship
between a URI 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 (stored 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 } }
who | g | mbox |
---|---|---|
"Bob Hacker" | <http://example.org/bob> | <mailto:bob@oldcorp.example.org> |
"Alice Hacker" | <http://example.org/alice> | <mailto:alice@work.example.org> |
This query finds the mbox
together with the
information in the default graph about the publisher.
<http://example.org/dft.ttl>
is just the IRI
used to form the default graph, not it's name.
When querying a collection of graphs, the GRAPH
keyword is used to match patterns against named graphs. This is
by either using an IRI to select a graph or using a variable to
range over the IRIs naming graphs.
If D is a dataset {G, (<u1>, G1), ... }, and P is a graph pattern then S is a pattern solution of RDF Dataset Graph Pattern GRAPH(g, P) if either of:
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 .
[25] |
GraphGraphPattern |
::= | 'GRAPH' VarOrBlankNodeOrIRIref
GroupGraphPattern |
The query below matches the graph pattern on each of the
named graphs in the dataset and forms solutions which have the
src
variable bound to IRIs of the graph being
matched.
PREFIX foaf: <http://xmlns.com/foaf/0.1/> SELECT ?src ?bobNick 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:
src | bobNick |
---|---|
<http://example.org/foaf/aliceFoaf> | "Bobby" |
<http://example.org/foaf/bobFoaf> | "Robert" |
The query can restrict the matching applied to a specific
graph by supplying the graph 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 WHERE { GRAPH data:bobFoaf { ?x foaf:mbox <mailto:bob@work.example> . ?x foaf:nick ?nick } }
which yields a single solution:
nick |
---|
"Robert" |
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.
This can be used to find information in one part of a query,
and thus restrict the graphs matched in another part of the
query. 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 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 } }
mbox | nick | ppd |
---|---|---|
<mailto:bob@work.example> | "Robert" | <http://example.org/foaf/bobFoaf> |
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.
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.
name | mbox | date |
---|---|---|
"Bob" | <mailto:bob@oldcorp.example.org> | "2004-12-06"^^xsd:date |
"Bob" | <mailto:bob@newcorp.example.org> | "2005-01-10"^^xsd:date |
The IRI for the date datatype has been abbreviated in the results for clarity.
SPARQL has four query result forms. These result forms use the solutions from pattern matching to form result sets or RDF graphs. The query result 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.
- DESCRIBE
- Returns an RDF graph that describes the resources found.
- ASK
- Returns a boolean indicating whether a query pattern matches or not.
The SPARQL Variable Binding
Results XML Format can be used to serialize result sets from
a SELECT
query or the boolean result of an
ASK
query.
Query patterns generate an unordered collection of solutions, each solution being a function from variables to RDF terms. These solutions are then treated as a 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 SPARQL result forms.
Definition: Solution Sequence
A solution sequence S is a list of solutions.
S = ( S0, S1, . . . , Sn)
The solution sequence from matching the query pattern is a collection formed from the solutions of the query pattern with no defined order.
Definition: Solution Sequence Modifier
A solution sequence modifier is one of:
If SM is the set of modifiers, and QS is the collection of solutions of a query, we write SM(QS) for the sequence formed by applying SM to the solution sequence formed from QS.
The elements of a sequence of solutions can be modified by:
ORDER BY
: put the solutions in orderDISTINCT
: ensure solutions in the sequence are
uniqueOFFSET
: control where the solutions processed
start from in the overall sequence of solutionsLIMIT
: restrict the number of solutions
processed for query resultsapplied in the order given by the list.
The ORDER BY
clause takes a solution sequence and
applies an ordering condition based on all the expressions and directions
specified in the ORDER BY
clause. The ordering condition also
involves a direction of
ordering which is ascending by default. It can be explicitly set to
ascending or descending by enclosing the condition in
ASC()
or DESC()
respectively. If
multiple expressions are given, then they are applied in turn until one gives the indication of the ordering.
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/> PREFIX xsd: <http://www.w3.org/2001/XMLSchema#> SELECT ?name WHERE { ?x foaf:name ?name ; :empId ?emp } ORDER BY DESC(?emp)
PREFIX foaf: <http://xmlns.com/foaf/0.1/> SELECT ?name WHERE { ?x foaf:name ?name ; :empId ?emp } ORDER BY ?name DESC(?emp)
Using ORDER BY
on a solution sequence for a
result form other than SELECT
has no direct effect
because only SELECT
returns a sequence of results.
In combination with LIMIT
and OFFSET
,
it can be used to return partial results.
An ordered solution sequence is a solution sequence where the sequence is partially ordered with respect to some ordering condition.
A solution sequence S = ( S0, S1, . . . , Sn) is ordered with respect to an ordering condition C if, for Si, Sj, then i < j if C orders Si before Sj.
An ordering condition need not give a total ordering of a solution sequence.
The "<" operator (see the Operator Mapping) defines the relative
order of pairs of numerics
,
xsd:dateTimes
and xsd:strings
.
IRIs are ordered by comparing the character strings making up each IRI using the "<" operator.
SPARQL also defines a fixed, arbitrary order between some
kinds of RDF terms that would not otherwise be ordered. This
arbitrary order is necessary to provide slicing of query
solutions by use of LIMIT
and
OFFSET
.
xsd:string
of the same lexical form.If the ordering criteria do not specify the order of values, then the ordering in the solution sequence is undefined.
Ordering a sequence of solutions always results in a sequence with the same number of solutions in it, even if the ordering criteria does not differentiate between two solutions.
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.
Definition: Projection
The projection of solution
QS over a set of variables VS is the solution
project(QS, VS) = { (v, QS(v)) | v in VS }
For a solution sequence S = ( S0, S1,
. . . , Sn) and a finite set of variables VS,
project(S, VS) = ( project(S0, VS), project(S1,
VS), . . . , project(Sn, VS) )
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" |
The solution sequence can be modified by adding the
DISTINCT
keyword which ensures that every
combination of variable bindings (i.e. each solution) in the
sequence is unique.
@prefix foaf: <http://xmlns.com/foaf/0.1/> . _:a foaf:name "Alice" . _:a foaf:mbox <mailto:alice@org> . _:z foaf:name "Alice" . _:z foaf:mbox <mailto:smith@work> .
PREFIX foaf: <http://xmlns.com/foaf/0.1/> SELECT DISTINCT ?name WHERE { ?x foaf:name ?name }
name |
---|
"Alice" |
If DISTINCT
and
LIMIT
or OFFSET
are specified, then
duplicates are eliminated before the limit or offset is
applied.
Definition: Distinct Solution Sequence
A Distinct Solution Sequence is a solution sequence in which no two solutions are the same.
Let Sx and Sy be pattern
solutions
then Sx != Sy if there exists variable v such that Sx(v) != Sy(v).
Equivalence of RDF terms is defined in Resource Description Framework (RDF): Concepts and Abstract Syntax [CONCEPTS].
For a solution sequence S = ( S1, S2, . . . , Sn), then write set(S) for the set of solution sequences in S.
distinct(S) = (Si | Si != Sj for all i != j) and set(distinct(S)) = set(S)
OFFSET
causes the solutions generated to start
after the specified number of solutions. An OFFSET
of zero has no effect.
The order in which solutions are returned is initially
undefined. 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
An Offset Solution Sequence with respect to another solution sequence S, is one which starts at a given index of S.
For solution sequence S = (S0, S1, . .
. , Sn), the offset solution sequence
offset(S, k), k >= 0 is
(Sk, Sk+1, . . ., Sn) if n
>= k
(), the empty sequence, if k > n
The LIMIT form puts an upper bound on the number of solutions returned. If the number of actual solutions 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.
Definition: Limited Solution Sequence
A Limited Solution Sequence has at most a given, fixed number of members.
The limit of solution sequence S = (S0, S1, . . . , Sn) is
limit(S, m) =
(S0, S1, . . . , Sm-1) if n
> m
(S0, S1, . . . , Sn) if n
<= m-1
The SELECT form of results returns the variables directly. The
syntax SELECT *
is an abbreviation that selects all
of the variables in a query.
@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 } }
nameX | nameY | nickY |
---|---|---|
"Alice" | "Bob" | |
"Alice" | "Clare" | "CT" |
Results can be thought of as a table or result set, with one row per query solution. Some cells may be empty because a variable is not bound in that particular solution.
Result sets can be accessed by a local API but also can be serialized into either XML or an RDF graph. An XML format is described in SPARQL Query Results XML Format, and this gives:
<?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>
Definition: SELECT
Given Q = (GP, DS, SM, SELECT VS) where
then, if QS is the set of solutions formed by matching dataset DS with graph pattern GP, the SELECT result is project(SM(QS), VS)
The CONSTRUCT
result 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 into 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 ground or explicit triples, that is, triples with no variables, 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 across 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 (which have labels _:a
and _:b
in the data) causes different blank node
labels (_:v1
and _:v2
) as shown by the
results.
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. Suppose 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#> 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
identified an extension function to turn the data
format into an xsd:dateTime
RDF Term.
Definition: Graph Template
A graph template is a set of triple patterns.
If T = { tj | j = 1,2 ... m } is a graph template and S is a pattern solution then SC(S, tj) is a set of one RDF triple S(tj) if all variables in tj are in the domain of S. SC(S, tj) is the empty set otherwise.
Write SC(S, T) for the union of SC(S, tj).
Definition: CONSTRUCT
Let Q = (GP, DS, SM, CONSTRUCT T) where
then, if QS is the set of solutions formed by matching dataset DS with graph pattern GP, then write SM(QS) = { Si | i = 1,2 ... n }.
Let Ti be a sequence of sets of triple patterns, such that each Ti is basic graph pattern equivalent to T and no Ti have a blank node in common and no Ti has a blank node in common with any blank node in SM(QS).
Let Ri be the RDF graph formed from SC(Si, Ti).
The CONSTRUCT result is the RDF graph formed by the union of Ri.
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 2 of
the solutions from graph pattern matching. The query outputs a
graph with the names of the people with the top 2 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" .
Current conventions for DESCRIBE
return an RDF graph without any specified constraints. Future
SPARQL specifications may further constrain the results of
DESCRIBE
, rendering some currently valid
DESCRIBE
responses invalid. As with any query, a
service may refuse to serve a DESCRIBE
query.
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" from the target
knowledge base. The description is determined by the query
service. The syntax DESCRIBE *
is an abbreviation that identifies 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 can also be a query variable from 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 function 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 is the useful information the service has about a resource. It may include information about other resources: 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 "ABCD1234" ;
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 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.
Definition: DESCRIBE
Let Q = (GP, DS, SM, DESCRIBE V) where
then, if QS is the set of solutions formed by matching
dataset DS with graph pattern GP, the DESCRIBE result is an RDF graph formed by
information relating elements of
distinct(U union project(SM(QS), VS)).
This definition intentionally does not prescribe the nature of the relevant information.
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 the server can
find one or not.
@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" }
yes
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> <results> <boolean>true</boolean> </results> </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> }
no
Definition: ASK
Let Q = (GP, DS, SM, ASK) where
and QS is the set of solutions formed by matching dataset DS with graph pattern GP then the ASK result is true if SM(QS) is not empty, otherwise it is false.
SPARQL FILTERs
restrict the set of solutions according to a given expression. 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 11.2.2 Effective Boolean Value; errors are defined in XQuery 1.0: An XML Query Language [XQUERY] section 2.3.1, Kinds of Errors.
As stated in section 4.1, RDF Terms are made of IRIs, Literals and Blank Nodes. 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 first dc:date
arc 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 11.3 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 11.5. The are invoked by name (an IRI) within a SPARQL query:
... FILTER ( xsd:dateTime(?date) < xsd:dateTime("2005-01-01T00:00:00Z") ) ...
The following typographical conventions are used in this section:
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
@@by reversing this mapping@@.
SPARQL has additional operators which operate on specific subsets of RDF terms. The following terms are imported from Resource Description Framework (RDF): Concepts and Abstract Syntax [CONCEPTS]:
RDF URI reference
")datatype
URI
")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 dervived from numeric types:
xsd:nonPositiveInteger
xsd:negativeInteger
xsd:long
xsd:int
xsd:short
xsd:byte
xsd:nonNegativeInteger
xsd:unsignedLong
xsd:unsignedInt
xsd:unsignedShort
xsd:unsignedByte
xsd:positiveInteger
Extended SPARQL implementations may treat additional types as being derived from numeric types.
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
) will produce a type error. Functions requiring an argument of type xsd:boolean
are coerced to xsd:boolean
using the EBV rules in section 11.2.2 .||
) 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 and operators on a list of arguments. 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.
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
, 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 with a lexical value of "false".
[Informative: 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.]
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 11.4. 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 upper-most viable candiate 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 {xs:integer
, xs:decimal
, xs:float
, xs:double
, and types derived from a numeric type} apply to SPARQL operators as well (see XML Path Language (XPath) 2.0 [XPATH20] for defintions 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 equivilence can be tested with RDF term equivilence.
Operator | Type(A) | Function | Result type | |
---|---|---|---|---|
XQuery Unary Operators | ||||
! A | xsd:boolean | fn:not(A) | xsd:boolean | |
+ A | numeric | op:numeric-unary-plus(A) | numeric | |
- A | numeric | op:numeric-unary-minus(A) | numeric | |
SPARQL Tests, defined in section 11.4 | ||||
BOUND(A) | variable | bound(A) | xsd:boolean | |
isIRI(A) isURI(A) |
RDF term | isIRI(A) | xsd:boolean | |
isBLANK(A) | RDF term | isBlank(A) | xsd:boolean | |
isLITERAL(A) | RDF term | isLiteral(A) | xsd:boolean | |
SPARQL Accessors | ||||
STR(A) | literal | str(A) | simple literal | |
STR(A) | IRI | str(A) | simple literal | |
LANG(A) | literal | lang(A) | simple literal | |
DATATYPE(A) | RDF term | datatype(A) | IRI |
Operator | Type(A) | Type(B) | Function | Result type |
---|---|---|---|---|
Logical Connectives, defined in section 11.4 | ||||
A || B | xsd:boolean | xsd:boolean | logical-or(A, B) | xsd:boolean |
A && B | xsd:boolean | xsd:boolean | 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, defined in section 11.4 | ||||
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 |
sameTERM(A) | RDF term | RDF term | sameTerm(A, B) | xsd:boolean |
langMATCHES(A, B) | simple literal | simple literal | langMatches(A, B) | xsd:boolean |
REGEX(STRING, PATTERN) | simple literal | simple literal | fn:matches(STRING, PATTERN) | xsd:boolean |
Operator | Type(A) | Type(B) | Type(C) | Function | Result type |
---|---|---|---|---|---|
SPARQL Tests, defined in section 11.4 | |||||
REGEX(STRING, PATTERN, FLAGS) | simple literal | simple literal | simple literal | fn:matches(STRING, PATTERN, FLAGS) | xsd:boolean |
Extended SPARQL implementations may support additional associations between operators and operator functions; this amounts to adding rows to the table above. No additional operator support may yield a result that replaces any result other than a type error in an unextended implementation. The consequence of this rule is that extended SPARQL implementations will produce at least the same solutions as an unextended implementation, and may, for some queries, produce more solutions.
This section defines the operators 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 a var
is bound to a value. Returns false otherwise. Variables with the value NaN or INF are considered bound. See 6.3 Unbound Variables for a discussion of why variables may be unbound.
@@ 6.3 may be removed.
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 ?name 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.
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 foaf:knows
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 11.4.2 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" |
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
.
@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
(RDF term
ltrl
)
Returns the datatype IRI
of ltrl
if ltrl
is a typed literal; returns xsd:string
if ltrl
is a simple literal; produces an error otherwise.
@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 |
xsd:boolean
xsd:boolean
left
||
xsd:boolean
right
Returns a logical OR
of left
and right
. As with other functions and operators with boolean arguments, logical-or
operates on the effective boolean value of its arguments.
Note: see section 11.2, 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
. As with other functions and operators with boolean arguments, logical-and
operates on the effective boolean value of its arguments.
Note: see section 11.2, 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:
term1
and term2
are equivalent IRIs as defined in 6.4 RDF URI References.term1
and term2
are equivalent literals as defined in 6.5.1 Literal Equality.term1
and term2
are the same blank node as described in 6.6 Blank Nodes.@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
arcs:
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 on New Year's Day (2004 or 2005), 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 types literals tests for equivilent 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 URI) 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
language-tag
,RDF term
language-range
)
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
arcs:
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-equivilent typed literals with unsupported data types:
@prefix : <http://example.org/WMterms#> . @prefix t: <http://example.org/types#> . _:c1 :label "Container 1" . _:c1 :weight "100"^^t:kilos . _:c1 :displacment "100"^^t:liters . _:c2 :label "Container 2" . _:c2 :weight "100"^^t:kilos . _:c2 :displacment "85"^^t:liters . _:c3 :label "Container 3" . _:c3 :weight "85"^^t:kilos . _:c3 :displacment "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. In the same way that pointer comparisons are usually more efficient than value comparisons, sameTerm is likely to be more efficient than RDFterm-equal. @@is that worth mentioning?@@
xsd:boolean
langMatches
(simple literal
language-tag
,simple literal
language-range
)
Returns true
if language-range
(second argument) matches language-tag
(first argument) per Tags for the Identification of Languages [RFC3066] section 2.5. RFC3066 @@reference rfc4647 (3066bis) term "well-formed" if the RFC is ready in time@@ defines a case-insensitive, hierarchical matching algorithm which operates on ISO-defined subtags for language and country codes, and user defined subtags. In SPARQL, 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
(described in section 11.2.3.8) 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
(simple literal
text
,simple literal
pattern
)xsd:boolean
regex
(simple 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" |
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 data types 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 |
A PrimaryExpression (see the grammar, production [55]) 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.
@@ Check the reference into the grammar
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:boolean
aGeo:distance
(numeric
x
,numeric
y
)
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 . . .
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. |
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 whitespace is significant; these
form a possible choice of terminals for constructing a SPARQL
parser. White space is significant in strings.
@@ Example ?a<?b&&?c>&d
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 Q_IRI_REF
production and QName
(after prefix
expansion) production, after escape processing, must be 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 Q_IRI_REF
<abc#def>
may occur in a SPARQL query string,
but the Q_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 see section 2.1.1, Syntax of IRI Terms, for a description of BASE and PREFIX.
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) |
where HEX is a hexadecimal character
HEX ::= [0-9] | [A-F] | [a-f]
Any escaped character in the range #x0 - #x10FFFF
may appear in any string production. For instance, "\n" may
appear in a
STRING_LITERAL1
even though the unescaped form is not
valid in that production.
Examples:
"abc\n" "xy\rz" 'xy\tz' 'a\u00E9'
The EBNF notation used in the grammar is defined in Extensible Markup Language (XML) 1.1 [XML11] section 6 Notation.
Keywords are matched in a case-insensitive manner with the exception of the keyword '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)
.
@@keywords are ...
Escape sequences are case sensitive.
When choosing a rule to match, the longest match is chosen.
The SPARQL grammar is LL(1) when the rules with uppercased names are used as terminals.
Some grammar files for some commonly used tools are avaiable here (parsers/).
See appendix A SPARQL Grammar regarding conformance of SPARQL Query strings, and section 10 Query Result Forms for conformance of query results. See appendix E. 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] and the SPARQL Query Results XML Format [RESULTS]. See those specifications for their conformance criteria.
Note that the SPARQL protocol describes an abstract interface as well as a network protocol, and the abstract interface may apply to APIs as well as network interfaces.
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.
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 collected formal definitions are collected into a single document "SPARQL Query Language for RDF - Formal Definitions".
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" (all lowercase) on all platforms.
It is recommended that sparql query files stored on Macintosh HFS file systems be given a file type of "TEXT".
This information that follows is intended to be submitted to the IESG for review, approval, and registration with IANA.
The SPARQL RDF Query Language is a product of the whole of the W3C RDF Data Access Working Group, and our thanks for discussions, comments and reviews go to all present and past members.
In addition, we have had comments and discussions with many people through the working group comments list. All comments go to making a better document. Andy would also like to particularly thank Geoff Chappell, Bob MacGregor, Yosi Scharf and Richard Newman for exploring specific issues related to SPARQL. Eric would like to acknowledge the invaluable help of Björn Höhrmann.
Changes since the 21 July 2005 Working Draft include design changes, for which the WG has or intends to have corresponding test cases:
and significant editorial changes:
Raw CVS log:
$Log: rq24.html,v $ Revision 1.45 2007/02/16 18:06:04 aseaborne Checkpoint Revision 1.44 2007/01/02 14:46:03 eric + = and != for simple literal and xsd:string Revision 1.43 2006/10/13 15:01:12 aseaborne Finish removing token UCHAR Revision 1.42 2006/10/12 12:58:09 aseaborne Editorial changes from 2006OctDec/0025 as described in 2006OctDec/0056 Grammar changed as detailed in 2006OctDec/0055 Revision 1.41 2006/10/10 11:31:54 aseaborne Fix HTML for validation ; truncate CVS log to rq24 start Revision 1.38 2006/10/02 14:06:14 aseaborne Remove red text about UNION objection that has been withdrawn Revision 1.37 2006/09/20 14:33:44 aseaborne Removed out-of-date editor notes. Changes to reflect the WG decisions on: + """ to support term distinctness w/r/t URIs and bnodes, with literals to be decided """ + """ Logical entailment may result in inconsistent RDF graphs. The result of queries on an inconsistent graph is outside this specification. """
Revision 1.36 2006/09/20 10:50:27 eric - Pending issues summary per Bijan's and Kendall's requests Revision 1.35 2006/09/19 16:07:21 eric - DISTINCT issue per WG decision Revision 1.34 2006/09/19 15:31:16 eric - inconsistent graph issue per WG decision Revision 1.33 2006/09/19 10:43:08 eric ~ updated Pending issues per discussion with Ralph, Ivan, Sandro, DanC 2006-09-18T14:18:55Z Revision 1.32 2006/09/15 08:22:57 aseaborne Added an @@ for filters in 4.7 Revision 1.31 2006/09/14 13:04:46 eric ~ [NON-EDITORIAL] DATATYE (RDF term) => IRI Revision 1.30 2006/09/14 11:48:02 eric + [NON-EDITORIAL] 11.4.10bis sameTerm + [EDITORIAL] explanation of RDFterm-equal type errors Revision 1.29 2006/09/13 19:52:52 aseaborne Editorial changes in response to /2006Sep/0003 as noted in /2006Sep/0004 Revision 1.28 2006/09/13 14:33:07 aseaborne Editorial changes based on comments by SimonR: 2006Sep/0000as noted in 2006JulSep/??? Revision 1.27 2006/09/13 13:03:42 aseaborne Editorial changes based on telecon of 2006/09/12: - Remove section discussion D-entailment (4.8) + Add text in 4.7 that restrictions by value only apply to RDF literals. Revision 1.25 2006/09/12 12:33:01 aseaborne Fix validation errors Revision 1.23 2006/09/11 17:16:39 aseaborne Editorial changes based on comments by LeeF: 2006JulSep/0108 (partial commit) Revision 1.22 2006/09/11 12:42:05 aseaborne Editorial changes based on comments by LeeF: 2006JulSep/0107 as noted in 2006JulSep/0210 Revision 1.21 2006/09/09 10:38:57 eric + Pending issues list + issue descriptions, place in context in the document Revision 1.20 2006/09/08 12:34:12 eric + handle unbound arguments [addressed comment, proposed changes] ~ [EDITORIAL] changed the operator name "isBound" to "bound" because the distinct func name was unhelpful + [EDITORIAL] note 3066bis Revision 1.19 2006/09/08 11:19:29 eric + controversial extensibility text [announced] Revision 1.18 2006/09/06 08:04:12 aseaborne Type ; added an @@ Revision 1.17 2006/08/16 09:02:14 aseaborne Noted ToDo items for DISTINCT Revision 1.16 2006/08/15 17:20:26 aseaborne Add CVS date to head Revision 1.15 2006/08/15 11:39:11 eric + make RDFterm-equal produce a type error for != literals Revision 1.14 2006/08/15 11:37:18 eric ~ [EDITORIAL] rework Testing Values to facilitate adding extensibility Revision 1.13 2006/08/14 17:36:19 aseaborne Put back text for DISTINCT definition which gives the condition for DISTINCTness. Revision 1.12 2006/08/14 17:14:01 eric ~ [EDITORIAL] restructured 11.3 intro paragraphs Revision 1.11 2006/08/14 13:57:07 eric ~ [EDITORIAL] minor clarifications on filter functions Revision 1.10 2006/08/09 14:50:33 eric ~ copied 11 Testing Values markup from rq23 Revision 1.9 2006/07/26 12:31:08 aseaborne Added ties to the grammar from main body of doc - some still placeholders Revision 1.8 2006/07/24 10:35:43 aseaborne Reorganize appendix A. Move codepoint escape processing outside the grammar proper as per 2006JanMAr/0443. The grammar rules itself not updated for this chnage. Revision 1.7 2006/07/17 12:53:34 aseaborne Finish renumbering Revision 1.6 2006/07/13 17:05:01 aseaborne Editorial changes to wording in descriptive sections Revision 1.5 2006/07/06 10:44:28 aseaborne Validation fix Revision 1.4 2006/07/06 10:39:46 aseaborne Reorg old sections 7/8/9 (datasets) into one section (new 9) Revision 1.3 2006/07/04 13:35:51 aseaborne Missing space in section 4.1 title Revision 1.2 2006/07/04 13:33:02 aseaborne Ran tidy -i -asxhtml Revision 1.1 2006/07/04 13:31:16 aseaborne Draft reorganisation of sections