W3C


RIF Datatypes and Built-Ins 1.0

W3C Working Draft 18 December 2008

This version:
http://www.w3.org/TR/2008/WD-rif-dtb-20081218/
Latest version:
http://www.w3.org/TR/rif-dtb/
Previous version:
http://www.w3.org/TR/2008/WD-rif-dtb-20080730/
Editors:
Axel Polleres, DERI
Harold Boley, National Research Council Canada
Michael Kifer, State University of New York at Stony Brook

This document is also available in these non-normative formats: PDF version.

Copyright © 2008 W3C® (MIT, ERCIM, Keio), All Rights Reserved. W3C liability, trademark and document use rules apply.

Abstract

Status of this Document

May Be Superseded

This section describes the status of this document at the time of its publication. Other documents may supersede this document. A list of current W3C publications and the latest revision of this technical report can be found in the W3C technical reports index at http://www.w3.org/TR/.

This document is being published as one of a set of 5 documents:

  1. RIF Use Cases and Requirements
  2. RIF Core
  3. RIF Datatypes and Built-Ins 1.0 (this document)
  4. RIF Production Rule Dialect
  5. RIF Test Cases

Summary of Changes

In addition to various editorial improvements, the comparison predicates have been unified, and the "rif:text" datatype has been aligned with OWL 2 as rdf:text

Please Comment By 23 January 2009

The Rule Interchange Format (RIF) Working Group seeks public feedback on these Working Drafts. Please send your comments to public-rif-comments@w3.org (public archive). If possible, please offer specific changes to the text that would address your concern. You may also wish to check the Wiki Version of this document for internal-review comments and changes being drafted which may address your concerns.

No Endorsement

Publication as a Working Draft does not imply endorsement by the W3C Membership. This is a draft document and may be updated, replaced or obsoleted by other documents at any time. It is inappropriate to cite this document as other than work in progress.

Patents

This document was produced by a group operating under the 5 February 2004 W3C Patent Policy. W3C maintains a public list of any patent disclosures made in connection with the deliverables of the group; that page also includes instructions for disclosing a patent. An individual who has actual knowledge of a patent which the individual believes contains Essential Claim(s) must disclose the information in accordance with section 6 of the W3C Patent Policy.


This document, developed by the Rule Interchange Format (RIF) Working Group, specifies a list of primitive datatypes, built-in functions and built-in predicates expected to be supported by RIF dialects such as the RIF Basic Logic Dialect. Each dialect supporting a superset or subset of the primitive datatypes, built-in functions and built-in predicates defined here shall specify these additions or restrictions. Some of the datatypes are adopted from [XML-SCHEMA2]. A large part of the definitions of the listed functions and operators are adopted from [XPath-Functions]. The rdf:text datatype as well as functions and operators associated with that datatype are adopted from [RDF-TEXT].


Contents

1 Constants, Symbol Spaces, and Datatypes

1.1 Constants and Symbol Spaces

Each constant (that is, each non-keyword symbol) in RIF belongs to a particular symbol space. A constant in a particular RIF symbol space has the following presentation syntax:

"literal"^^<symbolSpaceIri>

where literal is called the lexical part of the symbol, and symbolSpaceIri is an (absolute or relative) IRI identifying the symbol space. Here literal is a Unicode string that must be an element in the lexical space of the symbol space identified by the IRI symbolSpaceIri.

1.2 The Base and Prefix Directives

Since IRI typically require long strings of characters, many Web languages have special provisions for abbreviating these strings. One popular technique is called compact URI [CURIE], and RIF uses a similar technique by allowing RIF documents to have the directives Base and Prefix.

The precise way in which these directives work is explained in Section Shortcuts for Constants in RIF's Presentation Syntax.

To avoid writing down long IRIs, this document will assume that the following Prefix directives have been specified in all the RIF documents under consideration:

Using these prefixes and the shorthand mechanism defined in Section Shortcuts for Constants in RIF's Presentation Syntax, we can, for example, abbreviate a constant such as "http://www.example.org"^^<http://www.w3.org/2007/rif#iri> into "http://www.example.org"^^rif:iri.

1.2.1 Symbol Spaces

Formally, we define symbol spaces as follows.

Definition (Symbol space). A symbol space is a named subset of the set of all constants, Const in RIF. Each symbol in Const belongs to exactly one symbol space.

Each symbol space has an associated lexical space, a unique IRI identifying it and a short name. More precisely,

The identifiers of symbol spaces are not themselves constant symbols in RIF.

For convenience we will often use symbol space identifiers to refer to the actual symbol spaces (for instance, we may use "symbol space xs:string" instead of "symbol space identified by xs:string").


RIF dialects are expected to include the following symbol spaces. However, rule sets that are exchanged through RIF can use additional symbol spaces.

Note that, by the associated lexical space, not all unicode strings are syntactically valid lexical parts for all symbol spaces. That is, for instance "1.2"^^xs:decimal and "1"^^xs:integer are syntactically valid constant because 1.2 and 1 are members of the lexical space of symbol spaces xs:decimal and xs:integer, respectively. On the other hand, "a+2"^^xs:decimal is not a syntactically valid constant, since a+2 is not part of the lexical space of xs:decimal.

We will often refer to constant symbols that come from a particular symbol space, X, as X-constants. For instance the constants in the symbol space rif:iri will be referred to as IRI constants or rif:iri constants and the constants found in the symbol space rif:local as local constants or rif:local constants.

1.2.2 Shortcuts for Constants in RIF's Presentation Syntax

Besides the basic notion

"literal"^^<identifier>

RIF's presentation syntax introduces several shortcuts for particular symbol spaces, in order to make the presentation syntax more readable. RIF's presentation syntax for constants is defined by the following EBNF. 

  ANGLEBRACKIRI ::= IRI_REF
  SYMSPACE      ::= ANGLEBRACKIRI | CURIE
  CURIE         ::= PNAME_LN | PNAME_NS
  Const         ::= '"' UNICODESTRING '"^^' SYMSPACE | CONSTSHORT
  CONSTSHORT    ::= ANGLEBRACKIRI              // shortcut for "..."^^rif:iri
                  | CURIE                      // shortcut for "..."^^rif:iri
                  | '"' UNICODESTRING '"'      // shortcut for "..."^^xs:string
                  | NumericLiteral             // shortcut for "..."^^xs:integer,xs:decimal,xs:double
                  | '_' LocalName              // shortcut for "..."^^rif:local
                  | '"' UNICODESTRING '"' '@' languageTag             // shortcut for "...@..."^^rdf:text

The EBNF grammar relies on reuse of nonterminals defined in the following grammar productions from other documents:

In this grammar, CURIE stands for compact IRIs [CURIE], which are used to abbreviate symbol space IRIs. For instance, one can write "http://www.example.org"^^rif:iri instead of "http://www.example.org"^^<http://www.w3.org/2007/rif#iri>, where rif is a prefix defined in Section Base and Prefix Directives. <p>Apart from compact IRIs, there exist convenient shortcut notations for constants in specific symbol spaces, namely for constants in the symbol spaces rif:iri, xs:string, xs:integer, xs:decimal, xs:double, and rif:local:

1.2.3 Relative IRIs

Relative IRIs in RIF documents are resolved with respect to the base IRI. Relative IRIs are combined with base IRIs as per Uniform Resource Identifier (URI): Generic Syntax [RFC-3986] 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 RFC-3986) 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) [RFC-3987].

Base IRIs are specified using the Base directive described in Section Base and Prefix Directives. At most one base directive per document is allowed. In the XML syntax, base IRIs are specified using the attribute xml:base.

For instance, the constant <./xyz> or "./xyz"^^rif:iri are both valid abbreviations in RIF for the constant http://www.example.org/xyz"^^rif:iri, if the following directive is present in the document:

Base(http://www.example.org)

1.3 Primitive Datatypes

Datatypes in RIF are symbol spaces which have special semantics. That is, each datatype is characterized by a fixed lexical space, value space and lexical-to-value-mapping.

Definition (Primitive datatype). A primitive datatype (or just a datatype, for short) is a symbol space that has

Semantic structures are always defined with respect to a particular set of datatypes, denoted by DTS. In a concrete dialect, DTS always includes the datatypes supported by that dialect. RIF dialects are expected to support the following primitive datatypes. However, RIF dialects may include additional datatypes.

Their value spaces and the lexical-to-value-space mappings are defined as follows:

Note that the value space and the lexical-to-value-space mapping for rdf:text defined here are compatible with RDF's semantics for string literals with named tags [RDF-SEMANTICS]. Moreover, the value space and the lexical-to-value-space mapping for xs:string are compatible with RDF's semantics for plain literals. RIF implementations MAY choose to interpret xs:string and its subtypes as subtypes of rdf:text following Section 3.1 of [RDF-TEXT], i.e., interpreting strings as texts with an empty language tag.

Editor's Note: Whether or not we allow the treatment of xs:string as a subtype of rdf:text in RIF implementations is still under discussion, cf. the mail thread starting at http://lists.w3.org/Archives/Public/public-rif-wg/2008Nov/0067.html.

Editor's Note: Some clarification is needed with respect to the value space of rdf:XMLLiteral which will hopefully be resolved by an erratum to the RDF spec., cf. the mail thread starting at http://lists.w3.org/Archives/Public/public-rif-wg/2008Dec/0013.html.

2 Syntax and Semantics of Built-ins

2.1 Syntax of Built-ins

A RIF built-in function or predicate is a special case of externally defined terms, which are defined in RIF Framework for Logic Dialects and also reproduced in the direct definition of RIF Basic Logic Dialect (RIF-BLD).

In RIF's presentation syntax built-in predicates and functions are syntactically represented as external terms of the form:

'External' '(' Expr ')'

where Expr is a positional term as defined in RIF Framework for Logic Dialects (see also in RIF Basic Logic Dialect). For RIF's normative syntax, see the XML Serialization Framework in RIF-FLD, or, specifically for RIF-BLD, see XML Serialization Syntax for RIF-BLD.

RIF-FLD introduces the notion of an external schema to describe both both the syntax and semantics of exernally defined terms. In the special case of a RIF built-in, external schemas have an especially simple form. A built-in named f that takes n arguments has the schema

( ?X1 ... ?Xn;   f(?X1 ... ?Xn) )

Here f(?X1 ... ?Xn) is the actual term that is used to refer to the built-in (in expressions of the form External(f(?X1 ... ?Xn))) and ?X1 ... ?Xn is the list of all variables in that term.

For convenience, a complete definition of external schemas is reproduced in Appendix: Schemas for Externally Defined Terms.


2.2 Semantics of Built-ins

The semantics of external terms in RIF-FLD and RIF-BLD is defined using two mappings: Iexternal and Itruth ο Iexternal.

3 List of RIF Built-in Predicates and Functions

This section provides a catalogue defining the syntax and semantics of a list of built-in predicates and functions in RIF. For each built-in, the following is defined:

  1. The name of the built-in.
  2. The external schema of the built-in.
  3. For a built-in function, how it maps its arguments into a result.

    As explained in Section Semantics of Built-ins, this corresponds to the mapping Iexternal(σ) in the formal semantics of RIF-FLD and RIF-BLD, where σ is the external schema of the built-in.

  4. For a built-in predicate, its truth value when the arguments are substituted with values in the domain.

    As explained in Section Semantics of Built-ins, this corresponds to the mapping Itruth ο Iexternal(σ) in the formal semantics of RIF-FLD and RIF-BLD, where σ is the external schema of the built-in.

  5. The domains for the arguments of the built-in.

    Typically, built-in functions and predicates are defined over the value spaces of appropriate datatypes, i.e. the domains of the arguments. When an argument falls outside of its domain, it is understood as an error. Since this document defines a model-theoretic semantics for RIF built-ins, which does not support the notion of an error, the definitions leave the values of the built-in predicates and functions unspecified in such cases. This means that if one or more of the arguments is not in its domain, the value of Iexternal(σ)(a1 ... an) is unspecified. In particular, this means it can vary from one implementation to another. Similarly, Itruth ο Iexternal(σ)(a1 ... an) is unspecified when an argument is not in its domain.

    This indeterminacy in case of an error implies that applications should not make any assumptions about the values of built-ins in such situations. Implementations are even allowed to abort in such cases and the only safe way to communicate rule sets that contain built-ins among RIF-compliant systems is to use datatype guards.


Many built-in functions and predicates described below are adapted from [XPath-Functions] and, when appropriate, we will refer to the definitions in that specification in order to avoid copying them.

3.1 Guard Predicates for Datatypes

RIF defines guard predicates for all datatypes in Section Primitive Datatypes.

Accordingly, the following schemas are defined.

3.1.1 pred:isInteger

3.1.2 pred:isDecimal

3.1.3 pred:isDouble

3.1.4 pred:isString

3.1.5 pred:isTime

3.1.6 pred:isDate

3.1.7 pred:isDateTime

3.1.8 pred:isDayTimeDuration

3.1.9 pred:isYearMonthDuration

3.1.10 pred:isXMLLiteral

3.1.11 pred:isText

Future dialects may extend this list of guards to other datatypes, but RIF does not require guards for all datatypes.

3.2 Negative Guard Predicates for Datatypes

Likewise, RIF defines negative guard predicates for all datatypes in Section Primitive Datatypes.

Accordingly, the following schemas are defined.

3.2.1 pred:isNotInteger

3.2.2 pred:isNotDecimal

3.2.3 pred:isNotDouble

3.2.4 pred:isNotString

3.2.5 pred:isNotTime

3.2.6 pred:isNotDate

3.2.7 pred:isNotDateTime

3.2.8 pred:isNotDayTimeDuration

3.2.9 pred:isNotYearMonthDuration

3.2.10 pred:isNotXMLLiteral

3.2.11 pred:isNotText

Future dialects may extend this list of guards to other datatypes, but RIF does not require negative guards for all datatypes.

3.3 Datatype Conversion and Datatypes Checking

In the following, we adapt several cast functions according to the conversions defined in Section 17.1 of [XPath-Functions]. Note that some of these conversions are only partially defined, which affects the domains of these cast functions.

Editor's Note: Due to the subtle differences in casting, e.g., concerning error handling, between RIF and [XPath-Functions], the definitions of cast functions might still need refinement in terms of defining the domains in future versions of this draft. Also, the definition of the mappings need refinement. See e-mail, esp. the response to item 6)

Likewise we define a conversion predicate useful for converting between rif:iri constants and strings, as well as a predicate to check the datatype of a constant.

3.3.1 xs:double

3.3.2 xs:integer

3.3.3 xs:decimal

3.3.4 xs:time

3.3.5 xs:date

3.3.6 xs:dateTime

3.3.7 xs:dayTimeDuration

3.3.8 xs:yearMonthDuration

3.3.9 xs:string

Note: Since RIF implementations MAY choose to interpret xs:string and its subtypes as subtypes of rdf:text following Section 3.1 of [RDF-TEXT], in such implementations this cast function also serves for conversions to rdf:text.


Editor's Note: Whether or not we allow the treatment of xs:string as a subtype of rdf:text in RIF implementations is still under discussion, cf. the mail thread starting at http://lists.w3.org/Archives/Public/public-rif-wg/2008Nov/0067.html.


Editor's Note: Casting from rdf:XMLLiteral to xs:string is still under discussion.

3.3.10 rdf:XMLLiteral

3.3.11 pred:iri-string

Conversions from rif:iri to xs:string and vice versa cannot be defined by the casting functions as above since rif:iri is not a datatype with a well-defined value space.

To this end, since conversions from IRIs (resources) to strings are a needed feature for instance for conversions between RDF formats (see example below), we introduce a built-in predicate which supports such conversions.

3.3.12 pred:hasDatatype

Extractions of the Datatype from a constant cannot be defined by a function (like for instance in SPARQL's datatype function) since the value spaces of datatypes may overlap.

To this end, we introduce a built-in predicate which supports extraction of the datatypes for a constant at hand.

Editor's Note: It is still under discussion in the WG whether this predicate should restrict the domain of the second argument rather to strings that represent valid IRIs than just being true for any constants that have the same interpretation as the particular rif:iri representing the datatype.

This predicate can be usable for extracting the datatype from a constant but due to the overlap of the calue spaces of datatypes, such extraction is not necessarily unique; for example, the following is entailed in any RIF ruleset:

  And ( External( pred:hasDatatype( "1.0"^^xs:decimal xs:decimal ) )
        External( pred:hasDatatype( "1.0"^^xs:decimal xs:integer ) )
        External( pred:hasDatatype( "1.0"^^xs:decimal xs:double  ) ) )

Editor's Note: Note that this example shows that pred:hasDatatype is not adequate for emulating SPARQL's datatype function http://www.w3.org/TR/rdf-sparql-query/#func-datatype, cf. the mail thread starting at http://lists.w3.org/Archives/Public/public-rif-wg/2008Nov/0067.html

The following example shows that also whether or not a RIF implementation that treats xs:string as a subtype of rdf:text may affect the entailments for pred:hasDatatype:

  Forall ?X (
    ?P [ ex:nameType -> ?D ] :-  
          And ( ?P[ foaf:name -> ?N ]
                External( pred:hasDatatype( ?N ?D ) ) )
  ex:alice [foaf:name -> "Alice"]

In a RIF implementation that treats xs:string as a subtype of rdf:text, following Section 3.1 of [RDF-TEXT], this ruleset would entail both ex:alice [ex:nameType -> rdf:text] and ex:alice [ex:nameType -> xs:string].

Editor's Note: Whether or not we allow the treatment of xs:string as a subtype of rdf:text in RIF implementations is still under discussion, cf. the mail thread starting at http://lists.w3.org/Archives/Public/public-rif-wg/2008Nov/0067.html.

Editor's Note: It is still under discussion in the WG whether an additional predicate pred:hasNotDatatype should be added, cf. ISSUE-80.

3.4 Numeric Functions and Predicates

The following functions and predicates are adapted from the respective numeric functions and operators in [XPath-Functions].

3.4.1 Numeric Functions

The following numeric built-in functions func:numeric-add, func:numeric-subtract, func:numeric-multiply, func:numeric-divide, func:numeric-integer-divide, and func:numeric-mod are defined in accordance with their corresponding operators in [XPath-Functions].

3.4.1.1 func:numeric-add (adapted from op:numeric-add)

3.4.1.2 func:numeric-subtract (adapted from op:numeric-subtract)

3.4.1.3 func:numeric-multiply (adapted from op:numeric-multiply)

3.4.1.4 func:numeric-divide (adapted from op:numeric-divide)

3.4.1.5 func:numeric-integer-divide (adapted from op:numeric-integer-divide)

3.4.1.6 func:numeric-mod (adapted from op:numeric-mod)

3.4.2 Numeric Predicates

3.4.2.1 pred:numeric-equal (adapted from op:numeric-equal)

The following numeric built-in predicates pred:numeric-less-than and pred:numeric-greater-than are defined analogously with respect to their corresponding operators in [XPath-Functions].

3.4.2.2 pred:numeric-less-than (adapted from op:numeric-less-than)

3.4.2.3 pred:numeric-greater-than (adapted from op:numeric-greater-than)

3.4.2.4 pred:numeric-not-equal

The predicate pred:numeric-not-equal has the same domains as pred:numeric-equal and is true whenever pred:numeric-equal is false.

3.4.2.5 pred:numeric-less-than-or-equal

The predicate pred:numeric-less-than-or-equal has the same domains as pred:numeric-equal and is true whenever pred:numeric-equal is true or pred:numeric-less-than is true.

3.4.2.6 pred:numeric-greater-than-or-equal

The predicate pred:numeric-greater-than-or-equal has the same domains as pred:numeric-equal and is true whenever pred:numeric-equal is true or pred:numeric-greater-than is true.

3.5 Functions and Predicates on Strings

The following functions and predicates are adapted from the respective functions and operators on strings in [XPath-Functions].

Editor's Note: The following treatment of built-ins which may have multiple arities is a strawman proposal currently under discussion in the working group.

In the following, we encounter several versions of some built-ins with varying arity, since XPath and XQuery allow overloading, i.e. the same function or operator name occurring with different arities. We treat this likewise in RIF, by numbering the different versions of the respective built-ins and treating the unnumbered version as syntactic sugar, i.e. for instance instead of External( func:concat2( str1, str2) ) and External( func:concat3( str1 str2 str3 ) ) we allow the equivalent forms External( func:concat( str1, str2) ) and External( func:concat( str1 str2 str3 ) ). Note that this is really purely syntactic sugar, and does not mean that for external predicates and functions we lift the restriction made in BLD that each function and predicate has a unique assigned arity. Those schemata for which we allow this syntactic sugar, appear in the same box.

3.5.1 Functions on Strings

3.5.1.1 func:compare (adapted from fn:compare)


The following schemata are defined analogously with respect to their corresponding functions and operators as defined in [XPath-Functions] and we only give informal descriptions of the respective mappings Iexternal.

3.5.1.2 func:concat (adapted from fn:concat)

3.5.1.3 func:string-join (adapted from fn:string-join)

3.5.1.4 func:substring (adapted from fn:substring)

3.5.1.5 func:string-length (adapted from fn:string-length)

3.5.1.6 func:upper-case (adapted from fn:upper-case)

3.5.1.7 func:lower-case (adapted from fn:lower-case)

3.5.1.8 func:encode-for-uri (adapted from fn:encode-for-uri)

3.5.1.9 func:iri-to-uri (adapted from fn:iri-to-uri)

3.5.1.10 func:escape-html-uri (adapted from fn:escape-html-uri)

3.5.1.11 func:substring-before (adapted from fn:substring-before)

3.5.1.12 func:substring-after (adapted from fn:substring-after)

3.5.1.13 func:replace (adapted from fn:replace)

3.5.2 Predicates on Strings

3.5.2.1 pred:contains (adapted from fn:contains)

The following schemata are defined analogously with respect to their corresponding functions as defined in [XPath-Functions] and we only give informal descriptions of the respective mappings Itruth ο Iexternal.

3.5.2.2 pred:starts-with (adapted from fn:starts-with)

3.5.2.3 pred:ends-with (adapted from fn:ends-with)

3.5.2.4 pred:matches (adapted from fn:matches)

Following the convention of having separate equality, inequality, less-than, greater-than, less-than-or-equal, greater-than-or-equal predicates for other datatypes, RIF defines such predicates as syntactic sugar over func:compare also for xs:string in the following.

Editor's Note: The need of separate less-than, greater-than, less-than-or-equal, greater-than-or-equal predicates for strings is still under discussion, cf. ISSUE-67.

3.5.2.5 pred:string-equal

3.5.2.6 pred:string-less-than

3.5.2.7 pred:string-greater-than

The following built-in predicates pred:string-not-equal, pred:string-less-than-or-equal and pred:string-greater-than-or-equal are defined accordingly.

3.5.2.8 pred:string-not-equal

The predicate pred:string-not-equal has the same domains as pred:string-equal and is true whenever pred:string-equal is false.

3.5.2.9 pred:string-less-than-or-equal

The predicate pred:string-less-than-or-equal has the same domains as pred:string-equal and is true whenever pred:string-equal is true or pred:string-less-than is true.

3.5.2.10 pred:string-greater-than-or-equal

The predicate pred:string-greater-than-or-equal has the same domains as pred:string-equal and is true whenever pred:string-equal is true or pred:string-greater-than is true.

3.6 Functions and Predicates on Dates, Times, and Durations

If not stated otherwise, in the following we define schemas for functions and operators defined on the date, time and duration datatypes in [XPath-Functions].

As defined in Section 3.3.2 Dates and Times, xs:dateTime, xs:date, xs:time, xs:gYearMonth, xs:gYear, xs:gMonthDay, xs:gMonth, xs:gDay values, referred to collectively as date/time values, are represented as seven components or properties: year, month, day, hour, minute, second and timezone. The value of the first five components are xs:integers. The value of the second component is an xs:decimal and the value of the timezone component is an xs:dayTimeDuration. For all the date/time datatypes, the timezone property is optional and may or may not be present. Depending on the datatype, some of the remaining six properties must be present and some must be absent. Absent, or missing, properties are represented by the empty sequence. This value is referred to as the local value in that the value is in the given timezone. Before comparing or subtracting xs:dateTime values, this local value must be translated or normalized to UTC.

3.6.1 Functions on Dates, Times, and Durations

3.6.1.1 func:year-from-dateTime (adapted from fn:year-from-dateTime)

Note that we we slightly deviate here from the original definition of fn:year-from-dateTime which says: "If ?arg is the empty sequence, returns the empty sequence." RIF predicates ad functions do not support "sequences". The following schemata are defined analogously with respect to their corresponding operators as defined in [XPath-Functions] and we only give informal descriptions of the respective mappings Iexternal.

3.6.1.2 func:month-from-dateTime (adapted from fn:month-from-dateTime)

3.6.1.3 func:day-from-dateTime (adapted from fn:day-from-dateTime)

3.6.1.4 func:hours-from-dateTime (adapted from fn:hours-from-dateTime)

3.6.1.5 func:minutes-from-dateTime (adapted from fn:minutes-from-dateTime)

3.6.1.6 func:seconds-from-dateTime (adapted from fn:seconds-from-dateTime)

3.6.1.7 func:year-from-date (adapted from fn:year-from-date)

3.6.1.8 func:month-from-date (adapted from fn:month-from-date)

3.6.1.9 func:day-from-date (adapted from fn:day-from-date)

3.6.1.10 func:hours-from-time (adapted from fn:hours-from-time)

3.6.1.11 func:minutes-from-time (adapted from fn:minutes-from-time)

3.6.1.12 func:seconds-from-time (adapted from fn:seconds-from-time)

3.6.1.13 func:years-from-duration (adapted from fn:years-from-duration)

3.6.1.14 func:months-from-duration (adapted from fn:months-from-duration)

3.6.1.15 func:days-from-duration (adapted from fn:days-from-duration)

3.6.1.16 func:hours-from-duration (adapted from fn:hours-from-duration)

3.6.1.17 func:minutes-from-duration (adapted from fn:minutes-from-duration)

3.6.1.18 func:seconds-from-duration (adapted from fn:seconds-from-duration)

3.6.1.19 func:timezone-from-dateTime (adapted from fn:timezone-from-dateTime)

The following two functions are defined analogously for domains xs:date and xs:time

3.6.1.20 func:timezone-from-date (adapted from fn:timezone-from-date)

3.6.1.21 func:timezone-from-time (adapted from fn:timezone-from-time)

3.6.1.22 func:subtract-dateTimes (adapted from op:subtract-dateTimes)

Subtracts two xs:dateTimes. Returns an xs:xs:dayTimeDuration.

3.6.1.23 func:subtract-dates (adapted from op:subtract-dates)

Subtracts two xs:dates. Returns an xs:xs:dayTimeDuration.

3.6.1.24 func:subtract-times (adapted from op:subtract-times)

Subtracts two xs:times. Returns an xs:xs:dayTimeDuration.

3.6.1.25 func:add-yearMonthDurations (adapted from op:add-yearMonthDurations)

Adds two xs:yearMonthDurations. Returns an xs:yearMonthDuration.

3.6.1.26 func:subtract-yearMonthDurations (adapted from op:subtract-yearMonthDurations)

Subtracts one xs:yearMonthDuration from another. Returns an xs:yearMonthDuration.

3.6.1.27 func:multiply-yearMonthDuration (adapted from op:multiply-yearMonthDuration)

Multiplies an xs:yearMonthDuration by an xs:double. Returns an xs:yearMonthDuration.

3.6.1.28 func:divide-yearMonthDuration (adapted from op:divide-yearMonthDuration)

Divides an xs:yearMonthDuration by an xs:double. Returns an xs:yearMonthDuration.

3.6.1.29 func:divide-by-yearMonthDuration (adapted from op:divide-yearMonthDuration-by-yearMonthDuration)

Divides an xs:yearMonthDuration by an xs:yearMonthDuration. Returns an xs:decimal.

3.6.1.30 func:add-dayTimeDurations (adapted from op:add-dayTimeDurations)

Adds two xs:dayTimeDurations. Returns an xs:dayTimeDuration.

3.6.1.31 func:subtract-dayTimeDurations (adapted from op:subtract-dayTimeDurations)

Subtracts one xs:dayTimeDuration from another. Returns an xs:dayTimeDuration.

3.6.1.32 func:multiply-dayTimeDuration (adapted from op:multiply-dayTimeDuration)

Multiplies an xs:dayTimeDuration by a xs:double. Returns an xs:dayTimeDuration.

3.6.1.33 func:divide-dayTimeDuration (adapted from op:divide-dayTimeDuration)

Divides an xs:dayTimeDuration by an xs:double. Returns an xs:dayTimeDuration.

3.6.1.34 func:divide-dayTimeDuration-by-dayTimeDuration (adapted from op:divide-dayTimeDuration-by-dayTimeDuration)

Divides an xs:dayTimeDuration by an xs:dayTimeDuration. Returns an xs:decimal.

3.6.1.35 func:add-yearMonthDuration-to-dateTime (adapted from op:add-yearMonthDuration-to-dateTime)

Adds a xs:yearMonthDuration (?arg2) to a xs:dateTime (?arg1). Returns an xs:dateTime.

3.6.1.36 func:add-yearMonthDuration-to-date (adapted from op:add-yearMonthDuration-to-date)

Adds a xs:yearMonthDuration (?arg2) to a xs:date (?arg1). Returns an xs:date.

3.6.1.37 func:add-dayTimeDuration-to-dateTime (adapted from op:add-dayTimeDuration-to-dateTime)

Adds a xs:dayTimeDuration (?arg2) to a xs:dateTime (?arg1). Returns an xs:dateTime.

3.6.1.38 func:add-dayTimeDuration-to-date (adapted from op:add-dayTimeDuration-to-date)

Adds a xs:dayTimeDuration (?arg2) to a xs:date (?arg1). Returns an xs:date.

3.6.1.39 func:add-dayTimeDuration-to-time (adapted from op:add-dayTimeDuration-to-time)

Adds a xs:dayTimeDuration (?arg2) to a xs:time (?arg1). Returns an xs:time.

3.6.1.40 func:subtract-yearMonthDuration-from-dateTime (adapted from op:subtract-yearMonthDuration-from-dateTime)

Subtracts a xs:yearMonthDuration (?arg2) from a xs:dateTime (?arg1). Returns an xs:dateTime.

3.6.1.41 func:subtract-yearMonthDuration-from-date (adapted from op:subtract-yearMonthDuration-from-date)

Subtracts a xs:yearMonthDuration (?arg2) from a xs:date (?arg1). Returns an xs:date.

3.6.1.42 func:subtract-dayTimeDuration-from-dateTime (adapted from op:subtract-dayTimeDuration-from-dateTime)

Subtracts a xs:dayTimeDuration (?arg2) from a xs:dateTime (?arg1). Returns an xs:dateTime.

3.6.1.43 func:subtract-dayTimeDuration-from-date (adapted from op:subtract-dayTimeDuration-from-date)

Subtracts a xs:dayTimeDuration (?arg2) from a xs:date (?arg1). Returns an xs:date.

3.6.1.44 func:subtract-dayTimeDuration-from-time (adapted from op:subtract-dayTimeDuration-from-time)

Subtracts a xs:dayTimeDuration (?arg2) from a xs:time (?arg1). Returns an xs:time.

3.6.2 Predicates on Dates, Times, and Durations

3.6.2.1 pred:dateTime-equal (adapted from op:dateTime-equal)

The following schemata for comparison operators are defined analogously with respect to their corresponding operators as defined in [XPath-Functions], where the domain for both arguments is implicit by the operator name and we only give additional details on domains and mapping as needed.

3.6.2.2 pred:dateTime-less-than (adapted from op:dateTime-less-than)

3.6.2.3 pred:dateTime-greater-thanl (adapted from op:dateTime-greater-than)

3.6.2.4 pred:date-equal (adapted from op:date-equal)

3.6.2.5 pred:date-less-than (adapted from op:date-less-than)

3.6.2.6 pred:date-greater-than (adapted from op:date-greater-than)

3.6.2.7 pred:time-equal (adapted from op:time-equal)

3.6.2.8 pred:time-less-than (adapted from op:time-less-than)

3.6.2.9 pred:time-greater-than (adapted from op:time-greater-than)

3.6.2.10 pred:duration-equal (adapted from op:duration-equal)

3.6.2.11 pred:dateTimeDuration-less-than (adapted from op:dayTimeDuration-less-than)

3.6.2.12 pred:dayTimeDuration-greater-than (adapted from op:dayTimeDuration-greater-than)

3.6.2.13 pred:yearMonthDuration-less-than (adapted from op:yearMonthDuration-less-than)

3.6.2.14 pred:yearMonthDuration-greater-than (adapted from op:yearMonthDuration-greater-than)

3.6.2.15 pred:dateTime-not-equal

The predicate pred:dateTime-not-equal has the same domains as pred:dateTime-equal and is true whenever pred:dateTime-equal is false.

3.6.2.16 pred:dateTime-less-than-or-equal

The predicate pred:dateTime-less-than-or-equal has the same domains as pred:dateTime-equal and is true whenever pred:dateTime-equal is true or pred:dateTime-less-than is true.

3.6.2.17 pred:dateTime-greater-than-or-equal

The predicate pred:dateTime-greater-than-or-equal has the same domains as pred:dateTime-equal and is true whenever pred:dateTime-equal is true or pred:dateTime-greater-than is true.

3.6.2.18 pred:date-not-equal

The predicate pred:date-not-equal has the same domains as pred:date-equal and is true whenever pred:date-equal is false.

3.6.2.19 pred:date-less-than-or-equal

The predicate pred:date-less-than-or-equal has the same domains as pred:date-equal and is true whenever pred:date-equal is true or pred:date-less-than is true.

3.6.2.20 pred:date-greater-than-or-equal

The predicate pred:date-greater-than-or-equal has the same domains as pred:date-equal and is true whenever pred:date-equal is true or pred:date-greater-than is true.

3.6.2.21 pred:time-not-equal

The predicate pred:time-not-equal has the same domains as pred:time-equal and is true whenever pred:time-equal is false.

3.6.2.22 pred:time-less-than-or-equal

The predicate pred:time-less-than-or-equal has the same domains as pred:time-equal and is true whenever pred:time-equal is true or pred:time-less-than is true.

3.6.2.23 pred:time-greater-than-or-equal

The predicate pred:time-greater-than-or-equal has the same domains as pred:time-equal and is true whenever pred:time-equal is true or pred:time-greater-than is true.

3.6.2.24 pred:duration-not-equal

The predicate pred:duration-equal has the same domains as pred:duration-equal and is true whenever pred:duration-equal is false.


Editor's Note: The introduction of less-than-or-eaual and greater-than-or-equal predicates for dayTimeDuration and yearMonthDuration still needs a WG resolution.

3.6.2.25 pred:dayTimeDuration-less-than-or-equal

The predicate pred:dayTimeDuration-less-than-or-equal has the same domains as pred:dayTimeDuration-less-than and is true whenever pred:duration-equal is true or pred:dayTimeDuration-less-than is true.

3.6.2.26 pred:dayTimeDuration-greater-than-or-equal

The predicate pred:dayTimeDuration-greater-than-or-equal has the same domains as pred:dayTimeDuration-greater-than and is true whenever pred:duration-equal is true or pred:dayTimeDuration-greater-than is true.

3.6.2.27 pred:yearMonthDuration-less-than-or-equal

The predicate pred:yearMonthDuration-less-than-or-equal has the same domains as pred:yearMonthDuration-less-than and is true whenever pred:duration-equal is true or pred:yearMonthDuration-less-than is true.

3.6.2.28 pred:yearMonthDuration-greater-than-or-equal

The predicate pred:yearMonthDuration-greater-than-or-equal has the same domains as pred:yearMonthDuration-greater-than and is true whenever pred:duration-equal is true or pred:yearMonthDuration-greater-than is true.

3.7 Functions and Predicates on rdf:XMLLiterals

Editor's Note: Predicates for rdf:XMLLiteral such as at least comparison predicates (equals, not-equals) are still under discussion in the working group.

3.7.1 pred:XMLLiteral-equal

3.7.2 pred:XMLLiteral-not-equal

The predicate pred:time-not-equal has the same domains as pred:XMLLiteral-equal and is true whenever pred:XMLLiteral-equal is false.


3.8 Functions and Predicates on rdf:text

The following functions and predicates are adapted from the respective functions and operators in [RDF-TEXT].

Editor's Note: Issues which are still open in the rdf:text specification might imply future changes on the functions and predicates defined here. For instance reuse of the fn: namespace is still under discussion, cf. http://lists.w3.org/Archives/Public/public-rdf-text/2008OctDec/0020.html. Moreover, references and links to the [RDF-TEXT] document will be updated in future versions of this document.

3.8.1 Functions on rdf:text

3.8.1.1 func:text-from-string-lang (adapted from fn:text-from-string-lang)

3.8.1.2 func:text-from-string (adapted from fn:text-from-string)

Note: Since RIF implementations MAY choose to interpret xs:string and its subtypes as subtypes of rdf:text following Section 3.1 of [RDF-TEXT], in such implementations this function may just be implemented as the identity function.

3.8.1.3 func:string-from-text (adapted from fn:string-from-text)

3.8.1.4 func:lang-from-text (adapted from fn:lang-from-text)

3.8.1.5 func:text-compare (adapted from fn:text-compare)

3.8.1.6 func:text-length (adapted from fn:text-length)

3.8.2 Predicates on rdf:text

3.8.2.1 pred:matches-language-range (adapted from fn:matches-language-range)

Following the convention of having separate equality, inequality, less-than, greater-than, less-than-or-equal, greater-than-or-equal predicates for other datatypes, RIF defines such predicates as syntactic sugar over func:text-compare also for rdf:text in the following.

3.8.2.2 pred:text-equal

3.8.2.3 pred:text-less-than

3.8.2.4 pred:text-greater-than

The following built-in predicates pred:text-not-equal, pred:text-less-than-or-equal and text:text-greater-than-or-equal are defined accordingly.

3.8.2.5 pred:text-not-equal

The predicate pred:text-not-equal has the same domains as pred:text-equal and is true whenever pred:text-equal is false.

3.8.2.6 pred:text-less-than-or-equal

The predicate pred:text-less-than-or-equal has the same domains as pred:text-equal and is true whenever pred:text-equal is true or pred:text-less-than is true.

3.8.2.7 pred:text-greater-than-or-equal

The predicate pred:text-greater-than-or-equal has the same domains as pred:text-equal and is true whenever pred:text-equal is true or pred:text-greater-than is true.

Editor's Note: The need of separate less-than, greater-than, less-than-or-equal, greater-than-or-equal predicates for rdf:text is still under discussion, cf. ISSUE-67

4 References

[BCP-47]
BCP 47 - Tags for the Identification of Languages, A. Phillips, M. Davis, IETF, Sep 2006, ftp://ftp.rfc-editor.org/in-notes/bcp/bcp47.txt.

[BLD]
RIF Basic Logic Dialect Harold Boley, Michael Kifer, eds. W3C Working Draft, 30 July 2008, http://www.w3.org/TR/2008/WD-rif-bld-20080730/. Latest version available at http://www.w3.org/TR/rif-bld/.

[CURIE]
CURIE Syntax 1.0, M. Birbeck, S. McCarron, W3C Working Draft, 6 May 2008, http://www.w3.org/TR/2007/WD-curie-20071126/. Latest version available at http://www.w3.org/TR/curie/.

[RDF-CONCEPTS]
Resource Description Framework (RDF): Concepts and Abstract Syntax, G. Klyne, J. Carroll (Editors), W3C Recommendation, 10 February 2004, http://www.w3.org/TR/2004/REC-rdf-concepts-20040210/. Latest version available at http://www.w3.org/TR/rdf-concepts/.

[RDF-SEMANTICS]
RDF Semantics, P. Hayes, Editor, W3C Recommendation, 10 February 2004, http://www.w3.org/TR/2004/REC-rdf-mt-20040210/. Latest version available at http://www.w3.org/TR/rdf-mt/.

[RDF-SCHEMA]
RDF Vocabulary Description Language 1.0: RDF Schema, B. McBride, Editor, W3C Recommendation 10 February 2004, http://www.w3.org/TR/2004/REC-rdf-schema-20040210/. Latest version available at http://www.w3.org/TR/rdf-schema/.

[RDF-TEXT]
rdf:text: A Datatype for Internationalized Text , J. Bao, A. Polleres, B. Motik (Editors), W3C Working Draft 02 December 2008, http://www.w3.org/TR/2008/WD-rdf-text-20081202/. Latest version available at http://www.w3.org/TR/rdf-text/.

[RFC-3986]
RFC 3986 - Uniform Resource Identifier (URI): Generic Syntax, T. Berners-Lee, R. Fielding, L. Masinter, IETF, January 2005, http://www.ietf.org/rfc/rfc3986.txt.

[RFC-3987]
RFC 3987 - Internationalized Resource Identifiers (IRIs), M. Duerst and M. Suignard, IETF, January 2005, http://www.ietf.org/rfc/rfc3987.txt.

[SPARQL]
SPARQL Query Language for RDF, E. Prud'hommeaux, A. Seaborne (Editors), W3C Recommendation, World Wide Web Consortium, 12 January 2008, http://www.w3.org/TR/2008/REC-rdf-sparql-query-20080115/. Latest version available at http://www.w3.org/TR/rdf-sparql-query/.

[XDM]
XQuery 1.0 and XPath 2.0 Data Model (XDM), M. Fernández, A. Malhotra, J. Marsh, M. Nagy, N. Walsh (Editors), W3C Recommendation, World Wide Web Consortium, 23 January 2007. This version is http://www.w3.org/TR/2007/REC-xpath-datamodel-20070123/. Latest version available at http://www.w3.org/TR/xpath-datamodel/.

[XML-NS]
Namespaces in XML 1.1 (Second Edition), T. Bray, D. Hollander, A. Layman, R. Tobin (Editors), W3C Recommendation, World Wide Web Consortium, 16 August 2006, http://www.w3.org/TR/2006/REC-xml-names11-20060816/. Latest version available at http://www.w3.org/TR/xml-names11/.

[XML-SCHEMA2]
XML Schema Part 2: Datatypes Second Edition, P. V. Biron, A. Malhotra (Editors), W3C Recommendation, World Wide Web Consortium, 28 October 2004, http://www.w3.org/TR/2004/REC-xmlschema-2-20041028/. Latest version available at http://www.w3.org/TR/xmlschema-2/.

[XPath-Functions]
XQuery 1.0 and XPath 2.0 Functions and Operators, A. Malhotra, J. Melton, N. Walsh (Editors), W3C Recommendation, World Wide Web Consortium, 23 January 2007, http://www.w3.org/TR/2007/REC-xpath-functions-20070123/. Latest version available at http://www.w3.org/TR/xpath-functions/.

5 Appendix: Schemas for Externally Defined Terms

This section is an edited copy of a section from RIF Framework for Logic Dialects. It is reproduced here for convenience of readers familiar with the RIF-BLD document who might not have studied RIF-FLD.

This section defines external schemas, which serve as templates for externally defined terms. These schemas determine which externally defined terms are acceptable in a RIF dialect. Externally defined terms include RIF built-ins, but are more general. They are designed to also accommodate the ideas of procedural attachments and querying of external data sources. Because of the need to accommodate many difference possibilities, the RIF logical framework supports a very general notion of an externally defined term. Such a term is not necessarily a function or a predicate -- it can be a frame, a classification term, and so on.

Definition (Schema for external term). An external schema is a statement of the form (?X1 ... ?Xn; τ) where

The names of the variables in an external schema are immaterial, but their order is important. For instance, (?X ?Y;  ?X[foo->?Y]) and (?V ?W;  ?V[foo->?W]) are considered to be indistinguishable, but (?X ?Y;  ?X[foo->?Y]) and (?Y ?X;  ?X[foo->?Y]) are viewed as different schemas.

A term t is an instance of an external schema (?X1 ... ?Xn; τ) iff t can be obtained from τ by a simultaneous substitution ?X1/s1 ... ?Xn/sn of the variables ?X1 ... ?Xn with terms s1 ... sn, respectively. Some of the terms si can be variables themselves. For example, ?Z[foo->f(a ?P)] is an instance of (?X ?Y; ?X[foo->?Y]) by the substitution ?X/?Z  ?Y/f(a ?P).    ☐

Observe that a variable cannot be an instance of an external schema, since τ in the above definition cannot be a variable. It will be seen later that this implies that a term of the form External(?X) is not well-formed in RIF.

The intuition behind the notion of an external schema, such as (?X ?Y;  ?X["foo"^^xs:string->?Y]) or (?V;  "pred:isTime"^^rif:iri(?V)), is that ?X["foo"^^xs:string->?Y] or "pred:isTime"^^rif:iri(?V) are invocation patterns for querying external sources, and instances of those schemas correspond to concrete invocations. Thus, External("http://foo.bar.com"^^rif:iri["foo"^^xs:string->"123"^^xs:integer]) and External("pred:isTime"^^rif:iri("22:33:44"^^xs:time) are examples of invocations of external terms -- one querying an external source and another invoking a built-in.


Definition (Coherent set of external schemas). A set of external schemas is coherent if there is no term, t, that is an instance of two distinct schemas in the set.    ☐

The intuition behind this notion is to ensure that any use of an external term is associated with at most one external schema. This assumption is relied upon in the definition of the semantics of externally defined terms. Note that the coherence condition is easy to verify syntactically and that it implies that schemas like (?X ?Y;  ?X[foo->?Y]) and (?Y ?X;  ?X[foo->?Y]), which differ only in the order of their variables, cannot be in the same coherent set.

It is important to keep in mind that external schemas are not part of the language in RIF, since they do not appear anywhere in RIF statements. Instead, they are best thought of as part of the grammar of the language.