Mapping to RDF Graphs

W3C Editor's Draft 2628 November 2008

This version:

http://www.w3.org/2007/OWL/draft/ED-owl2-mapping-to-rdf-20081126/http://www.w3.org/2007/OWL/draft/ED-owl2-mapping-to-rdf-20081128/

Latest editor's draft:

http://www.w3.org/2007/OWL/draft/owl2-mapping-to-rdf/

Previous version:

http://www.w3.org/2007/OWL/draft/ED-owl2-mapping-to-rdf-20081121/http://www.w3.org/2007/OWL/draft/ED-owl2-mapping-to-rdf-20081126/ (color-coded diff)

Editors:

Peter F. Patel-Schneider, Bell Labs Research, Alcatel-Lucent

Boris Motik, Oxford University

Contributors:

Bernardo Cuenca Grau, Oxford University

Ian Horrocks, Oxford University

Bijan Parsia, TheUniversity of Manchester

Note : The complete list of contributorsAlan Ruttenberg, Science Commons (Creative Commons)

Michael Schneider, FZI Research Center for Information Technology

This document is being compiled and will be includedalso available in the next draft.these non-normative formats: PDF version.

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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May Be Superseded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/.

Set of Documents

This document is being published as one of a set of 11 documents:

1. Structural Specification and Functional-Style Syntax
2. Direct Semantics
3. RDF-Based Semantics
4. Conformance and Test Cases
5. Mapping to RDF Graphs (this document)
6. XML Serialization
7. Profiles
8. Quick Reference Guide
9. New Features and Rationale
10. Manchester Syntax
11. rdf:text :rdf:text: A Datatype for Internationalized Text

Please Comment By 2008-11-282008-12-01

The OWL Working Group seeks public feedback on these Working Drafts. Please send your comments to public-owl-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.

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This document defines mappings by means of which every OWL 2 ontology [OWL 2 Specification] can be mapped into an RDF graph and back. These transformations do not incur any change in the formal meaning of the ontology. More precisely, let O be any OWL 2 ontology, let T(O) be the RDF graph obtained by transforming O as specified in Section 2, and let O' be the OWL 2 ontology obtained by applying the reverse transformation from Section 3 to T(O); then, O and O' are logically equivalent — that is, they have exactly the same set of models.

The mappings presented in this document are backwards-compatible with that of OWL DL: every OWL DL ontology encoded as an RDF graph can be mapped into a valid OWL 2 ontology using the reverse-transformation from Section 3 such that the resulting OWL 2 ontology has exactly the same set of models as the original OWL DL ontology.

The syntax for triples used in this document is the one used in the RDF Semantics [RDF Semantics]. Full URIs are abbreviated using the namespaces from the OWL 2 Specification [OWL 2 Specification]. OWL 2 ontologies mentioned in this document should be understood as instances of the structural specification of OWL 2 [OWL 2 Specification]; when required, these are written in this document using the functional-style syntax.

The following notation is used throughout this document for referring to parts of RDF graphs:

• *:x denotes a URI reference;
• _:x denotes a blank node;
• x denotes a blank node or a URI reference; and
• lt denotes a literal.

The italicized keywords MUST, MUST NOT, SHOULD, SHOULD NOT, and MAY specify certain aspects of the normative behavior of OWL 2 tools, and are interpreted as specified in RFC 2119 [RFC 2119].

This section defines a mapping of an OWL 2 ontology O into an RDF graph T(O). The mapping is presented in three parts. Section 2.1 shows how to translate axioms that do not contain annotations, Section 2.2 shows how to translate annotations, and Section 2.3 shows how to translate axioms containing annotations.

The definition of the operator T uses the operator TANN in order to translate annotations. The operator TANN is defined in Section 2.2. It takes an annotation and an URI reference or a blank node and produces the triples that attach the annotation to the supplied object.

In the mapping, each generated blank node (i.e., each blank node that does not correspond to an anonymous individual) is fresh in each application of a mapping rule. Furthermore, the following conventions are used in this section to denote different parts of OWL 2 ontologies:

• OP denotes an object property;
• OPE denotes an object property expression;
• DP denotes a data property;
• DPE denotes a data property expression;
• PE denotes an object or a data property expression;
• AP denotes an annotation property;
• C denotes a class;
• CE denotes a class expression;
• DT denotes a datatype;
• DR denotes a data range;
• U denotes a URI;
• F denotes a constraining facet;
• a denotes an individual (named or anonymous);
• *:a denotes a named individual;
• lt denotes a literal;
• as denotes an annotation source; and
• av denotes an annotation value.

In this section, T(SEQ y₁ ... y_n) denotes the translation of a sequence of objects from the structural specification into an RDF list, as shown in Table 1.

An RDF syntax ontology document is a sequenceThis section specifies the results of octets accessible from some URI by meanssteps CP-2.2 and CP-3.3 of the standard protocols that can be parsed into an RDF graph G , which can then be transformed into an OWL 2 ontology according to thecanonical RDF parsing process defined in this section. Thisparsing process is specified as an instance of canonical parsing, defined infrom Section 3.6 of the OWL 2 Specification [OWL 2 Specification ]. It is important to understand] on an ontology document D that canonicalcan be parsed into an RDF parsing merely defines the result of the transformation.graph G. An OWL 2 implementationtool MAY implement whatever algorithmthese steps in any way it chooses; however, the resultresults MUST be structurally equivalent to the result of canonicalones defined in the following sections. These steps do not depend on the RDF parsing. Canonicalsyntax used to encode the RDF parsing maintainsgraph in D; therefore, the following functions that map a URI reference or a blank node x occurringontology document D is identified in this section with the corresponding RDF graph G into.

An objectRDF syntax ontology document is any sequence of the structural specification. In particular, CE(x) maps x into a class expression, DR(x) maps x into a data range, OPE(x) maps xoctets accessible from some given URI that can be parsed into an object property expression, DPE(x) maps x into a data property expression,RDF graph, and AP(x) maps xthat then be transformed into an annotation property. Initially, these functions are undefined for all URIs and blank nodes occurring in G ; this is written as CE(x) = ε , DR(x) = ε , OPE(x) = ε , DPE(x) = ε , and AP(x) = ε . The functions are updated as parsing progresses. All of the following conditions MUST be satisfied at any given point in time during parsing. For each x , at most one of OPE(x) , DPE(x) , and AP(x) is defined. For each x , at most one of CE(x) and DR(x) is defined. Furthermore,OWL 2 ontology by the value of any of these functions for any x MUST NOT be redefined duringcanonical parsing (i.e., if a function is not undefined for x , no attempt should be made to change the function's value for x ). The function OPEorDPE is definedprocess instantiated as follows: OPEorDPE(x) = OPE(x) if OPE(x) ≠ ε; OPEorDPE(x) = DPE(x) if DPE(x) ≠ ε; and OPEorDPE(x) = ε otherwise.specified in this section.

The following sections contain rules in which triple patterns are matched to G. If a triple pattern contains a variable number of triples, the maximal possible subset of G MUST be matched. The following notation is used in the patterns:

• The notation NN_INT(n) can be matched to any literal whose value n is a nonnegative integer.
• AdditionalPossible conditions on the pattern are enclosed in curly braces { }.
• Some patterns use optional parts, which are enclosed in square brackets '[ ]'.
• If a pattern contains a variable number of triples, the maximal possible subset of G MUST be matched.The abbreviation T(SEQ y₁ ... y_n) denotes the pattern corresponding to RDF lists, as shown in Table 3.

Next, the set of declarations Decl(G) is extracted from G according to Table 7. The matched triples are not removed from G — the triples from Table 7 can contain annotations so, in order to correctly parse the annotations, they will be matched again in the step described in Section 3.63.2.5.

Finally, the set RIND of anonymous individuals used in reification is identified. This is done by initially setting RIND = ∅ and then applying the patterns shown in Table 8. The matched triples are not deleted from G.

Next, functions OPE, DR, and CE are extended as shown in Tables 11, 12, and 13, as well as in Tables 14 and 15. The patterns in the latter two tables are not generated by the mapping from Section 2, but they can be present in RDF graphs that encode OWL DL ontologies. Each time a pattern is matched, the matched triples are removed from G. Pattern matching is repeated until no triple pattern can be matched to G.

Finally, the patterns from Table 18 are matched in G, the resulting axioms are added to O_G. These patterns are not generated by the mapping from Section 2, but they can be present in RDF graphs that encode OWL DL ontologies. (Note that the patterns from the table do not contain triples of the form *:x rdf:type owl:Class because such triples are removed while parsing the entity declarations, as specified in Section 3.23.1.2.) Each time a triple pattern is matched, the matched triples are removed from G.

At the end of this process, the graph G MUST be empty.

The Imported Ontologies All ontology documents directly imported into G are parsed according tostarting point for the rulesdevelopment of OWL 2 was the syntax they are written in.OWL1.1 member submission, itself a result of user and developer feedback, and in particular of information gathered during the resulting instancesOWL Experiences and Directions (OWLED) Workshop series. The working group also considered postponed issues from the WebOnt Working Group.

This document is the product of the Ontology class are addedOWL Working Group (see below) whose members deserve recognition for their time and commitment. The editors extend special thanks to the directlyImports associationreviewers of O . 3.8 Consistency Checkingthis and the structureother Working Group documents: Jie Bao (RPI), Kendall Clark (Clark & Parsia), Bernardo Cuenca Grau (Oxford University), Achille Fokoue (IBM Corporation), Jim Hendler (RPI), Ivan Herman (W3C/ERCIM), Rinke Hoekstra (University of O is checked, and O MUST be an OWL 2 ontology — that is, it must satisfy allAmsterdam), Ian Horrocks (Oxford University), Elisa Kendall (Sandpiper Software), Markus Krötzsch (FZI), Boris Motik (Oxford University), Jeff Pan (University of Aberdeen), Bijan Parsia (University of Manchester), Peter F. Patel-Schneider (Bell Labs Research, Alcatel-Lucent), Alan Ruttenberg (Science Commons), Uli Sattler (University of Manchester), Michael Schneider (FZI), Thomas Schneider (University of Manchester), Evren Sirin (Clark & Parsia), Mike Smith (Clark & Parsia), Vojtech Svatek (K-Space), and Zhe Wu (Oracle Corporation).

The restrictions listed in Section 3regular attendees at meetings of the OWL 2 Specification [ OWL 2 Specification ]. 4Working Group at the time of publication were: Jie Bao (RPI), Diego Calvanese (Free University of Bozen-Bolzano), Bernardo Cuenca Grau (Oxford University), Martin Dzbor (Open University), Achille Fokoue (IBM Corporation), Christine Golbreich (Université de Versailles St-Quentin), Sandro Hawke (W3C/MIT), Ivan Herman (W3C/ERCIM), Rinke Hoekstra (University of Amsterdam), Ian Horrocks (Oxford University), Elisa Kendall (Sandpiper Software), Markus Krötzsch (FZI), Carsten Lutz (Universität Bremen), Boris Motik (Oxford University), Jeff Pan (University of Aberdeen), Bijan Parsia (University of Manchester), Peter F. Patel-Schneider (Bell Labs Research, Alcatel-Lucent), Alan Ruttenberg (Science Commons), Uli Sattler (University of Manchester), Michael Schneider (FZI), Mike Smith (Clark & Parsia), Evan Wallace (NIST), Zhe Wu (Oracle Corporation)

We would also like to thank two past members of the working group: Jeremy Carroll, and Vipul Kashyap.

[OWL 2 Specification]

Structural Specification and Functional-Style Syntax Boris Motik, Peter F. Patel-Schneider, Bijan Parsia, eds. W3C Editor's Draft, 2628 November 2008, http://www.w3.org/2007/OWL/draft/ED-owl2-syntax-20081126/http://www.w3.org/2007/OWL/draft/ED-owl2-syntax-20081128/. Latest version available at http://www.w3.org/2007/OWL/draft/owl2-syntax/.

[RDF Semantics]

RDF Semantics. Patrick Hayes, Editor, W3C Recommendation, 10 February 2004

[RFC 2119]

RFC 2119: Key words for use in RFCs to Indicate Requirement Levels. Network Working Group, S. Bradner. Internet Best Current Practice, March 1997