Conformance-v2

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Document title:
OWL 2 Web Ontology Language
Conformance (Second Edition)

1 Conformance (Normative)

This section uses the words MUST, MUST NOT, SHOULD and MAY as in [RFC 2119].

1.1 Document Conformance

1.1.1 Syntactic Conformance

Any RDF/XML document [RDF Syntax] is an OWL 2 Full ontology document.

An OWL 2 Full ontology document is an OWL 2 DL ontology document iff it can be successfully parsed using the canonical RDF parsing process [OWL 2 Mapping to RDF Graphs] and the resulting ontology in the functional-style syntax satisfies all the restrictions on OWL 2 DL ontologies [OWL 2 Specification].

An OWL 2 DL ontology document is an OWL 2 EL ontology document iff it can be successfully parsed using the canonical RDF parsing process [OWL 2 Mapping to RDF Graphs] and the resulting ontology in the functional-style syntax satisfies all the restrictions on OWL 2 EL ontologies [OWL 2 Profiles].

An OWL 2 DL ontology document is an OWL 2 QL ontology document iff it can be successfully parsed using the canonical RDF parsing process [OWL 2 Mapping to RDF Graphs] and the resulting ontology in the functional-style syntax satisfies all the restrictions on OWL 2 QL ontologies [OWL 2 Profiles].

An OWL 2 Full ontology document is an OWL 2 RL ontology document iff it can be successfully parsed using the canonical RDF parsing process [OWL 2 Mapping to RDF Graphs] and the resulting ontology in the functional-style syntax satisfies all the restrictions on OWL 2 RL ontologies [OWL 2 Profiles].

1.1.2 Semantic Conformance

In OWL 2, semantic conditions are defined with respect to a datatype map [OWL 2 Specification]. This MUST be either an OWL Datatype map [OWL 2 Specification], or and extension of an OWL Datatype map to include additional datatypes.

  • An OWL 2 DL, EL or QL ontology O is consistent with respect to a datatype map M iff there exists a model with respect to M of the axiom closure of O [OWL 2 Semantics]. An OWL 2 DL, EL or QL ontology document D is consistent with respect to a datatype map M iff the ontology derived from D using the canonical RDF parsing process [OWL 2 Mapping to RDF Graphs] is consistent with respect to M.
  • An OWL 2 Full or OWL 2 RL ontology document D is consistent with respect to a datatype map M iff there is some OWL 2 Full interpretation of O with respect to M [OWL 2 RDF-Based Semantics].

1.2 Document Checker Conformance

1.2.1 Consistency Checker

An OWL 2 consistency checker checks the consistency of an OWL 2 ontology document with respect to a datatype map and either the Model-Theoretic Semantics [OWL 2 Semantics] or the RDF-Based Semantics [OWL 2 RDF-Based Semantics]. The datatype map MUST be either an OWL Datatype map [OWL 2 Specification], or and extension of an OWL Datatype map to include additional datatypes. Additionally:

  • It MUST provide a means to determine the datatypes supported by its datatype map, [OWL 2 Specification]; for example, by listing them in its supporting documentation.
  • It MUST provide a means to determine the semantics it uses (either the Model-Theoretic Semantics [OWL 2 Semantics] or the RDF-Based Semantics [OWL 2 RDF-Based Semantics]); for example, in its supporting documentation.

An OWL 2 consistency checker takes a document as input and returns one word, being Consistent, Inconsistent, or Unknown. Additionally:

  • It MUST report an error if the parsing process fails (e.g., due to network errors).
  • It MUST report an error if an input document uses datatypes that are not supported by its datatype map or literals that it does not support (e.g., very large integers).
  • It MUST be sound: it MUST return Consistent only when the input document is consistent and Inconsistent only when the input document is not consistent, with respect to the datatype map of the checker.
  • It SHOULD NOT return Unknown. While sometimes needed (e.g., for pragmatic reasons), Unknown is not a desired response.

Four different conformance classes of OWL consistency checker are defined:

An OWL 2 Full consistency checker is an OWL 2 consistency checker that takes an OWL 2 Full ontology document as input, and uses the RDF-Based Semantics [OWL 2 RDF-Based Semantics]; it MUST return Consistent only when the input document is consistent and Inconsistent only when the input document is not consistent.

An OWL 2 DL consistency checker is an OWL 2 consistency checker that takes an OWL 2 DL ontology document as input and uses the Model Theoretic Semantics [OWL 2 Semantics]; it MUST return Consistent only when the input document is consistent and Inconsistent only when the input document is not consistent.

An OWL 2 EL consistency checker is an OWL 2 consistency checker that takes an OWL 2 EL ontology document as input and uses the Model Theoretic Semantics [OWL 2 Semantics]; it MUST return Consistent only when the input document is consistent and Inconsistent only when the input document is not consistent.

An OWL 2 QL consistency checker is an OWL 2 consistency checker that takes an OWL 2 QL ontology document as input and uses the Model Theoretic Semantics [OWL 2 Semantics]; it MUST return Consistent only when the input document is consistent and Inconsistent only when the input document is not consistent.

An OWL 2 consistency checker is complete and terminating, if, given sufficient (but finite) resources (CPU cycles and memory) and the absence of network errors, it will always return either Consistent or Inconsistent. It has been shown that for OWL 2 DL, EL and QL it is possible to construct a complete and terminating consistency checker (the languages are decidable [SROIQ]), and that for OWL Full it is not possible to construct a complete and terminating consistency checker (the language is undecidable, [OWL Metamodeling]).

Note: An OWL 2 Full consistency checker may indicate that an ontology O is inconsistent, while an OWL 2 DL consistency checker indicates that an ontology O' is consistent, even when O and O' are derived from the same OWL 2 DL document (for example: Test???, ..., and Test???).

Note: Every OWL 2 DL consistency checker is also an OWL 2 EL and OWL 2 QL consistency checker.

Note: A complete and terminating OWL DL, EL or QL consistency checker MAY return Unknown in the case where a resource limit has been exceeded.

1.2.2 Entailment Checker

Some OWL 2 profiles, in particular OWL QL and OWL RL, are aimed mainly at data-centric applications. Checking implications (i.e., query answering) may be more relevant to such applications. An OWL 2 implication checker checks ground atomic implications for an OWL 2 ontology document with respect to a datatype map and either the Model-Theoretic Semantics [OWL 2 Semantics] or the RDF-Based Semantics [OWL 2 RDF-Based Semantics]. The datatype map MUST be either an OWL Datatype map [OWL 2 Specification], or and extension of an OWL Datatype map to include additional datatypes.

Given an assertion A, RDF(A) denotes the translation of A into an RDF graph as specified in the OWL 2 Mapping to RDF Graphs [OWL 2 RDF Mapping]. Given an RDF graph G, FO(G) denotes the FO theory corresponding to G in which triples are represented using the T predicate, i.e., T(s, p, o) represents an RDF triple with the subject s, predicate p, and the object o.

An OWL 2 implication checker returns one word, being True, False, or Unknown. Additionally:

  • It MUST report an error if the parsing process fails (e.g., due to network errors).
  • It MUST provide a means to determine the datatypes supported by its datatype map [OWL 2 Specification]; for example, by listing them in its supporting documentation.
  • It MUST provide a means to determine the semantics it uses (either the Model-Theoretic Semantics [OWL 2 Semantics] or the RDF-Based Semantics [OWL 2 RDF-Based Semantics]); for example, in its supporting documentation.
  • It MUST report an error if an input document uses datatypes that are not supported by its datatype map or literals that it does not support (e.g., very large integers).
  • It SHOULD NOT return Unknown. Unknown, while sometimes needed, is not a desired response.

Three different conformance classes of OWL implication checker are defined:

An OWL 2 Full implication checker is an OWL 2 implication checker that takes an OWL 2 Full ontology document D and an assertion A as input, and uses the RDF-Based Semantics [OWL 2 RDF-Based Semantics]; it MUST return True only when RDF(A) is entailed by D, and it must return False only when RDF(A) is not entailed by D.

An OWL 2 RL implication checker is an OWL 2 implication checker that takes an OWL 2 Full ontology document D and an assertion A as input, and uses the RDF-Based Semantics [OWL 2 RDF-Based Semantics]; it MUST return True only when RDF(A) is entailed by D, and it must return False only when FO(RDF(A)) is not entailed by FO(D)AXIOMS under the standard first-order semantics, where AXIOMS are the set of axioms given in the OWL 2 RL specification [OWL 2 Profiles]. An OWL 2 RL implication checker SHOULD report a warning if D is not an OWL 2 RL ontology document.

An OWL 2 QL implication checker is an OWL 2 implication checker that takes an OWL 2 QL ontology document D and an assertion A as input, and uses the Model Theoretic Semantics [OWL 2 Semantics]; it MUST return True only when A is entailed by D and False only when A is not entailed by D.

An OWL 2 implication checker is complete and terminating, if, given sufficient (but finite) resources (CPU cycles and memory) and the absence of network errors, it will always return either True or False, and it will return False only when the input assertion is not entailed by the input document. It is possible to construct a complete and terminating OWL 2 QL implication checker (the language is decidable). It is also possible to construct a complete and terminating OWL 2 RL implication checker, provided that the input is restricted to OWL 2 RL ontology documents. It is not possible to construct a complete and terminating OWL 2 Full implication checker (the language is undecidable, [OWL Metamodeling]).

Note: Every OWL 2 Full implication checker is also an OWL 2 RL implication checker.

2 References

[OWL 2 Specification]
OWL 2 Web Ontology Language: Structural Specification and Functional-Style Syntax. Peter F. Patel-Schneider, Ian Horrocks, and Boris Motik, eds., 2008.
[OWL 2 Semantics]
OWL 2 Web Ontology Language: Model-Theoretic Semantics. Bernardo Cuenca Grau and Boris Motik, eds., 2008.
[OWL 2 RDF-Based Semantics]
OWL 2 Web Ontology Language: RDF-Based Semantics. Michael Schneider, 2008.
[OWL 2 Profiles]
OWL 2 Web Ontology Language: Profiles. Bernardo Cuenca Grau, Boris Motik, Zhe Wu, Achille Fokoue and Carsten Lutz, 2008.
[RDF Syntax]
RDF/XML Syntax Specification (Revised). Dave Beckett, Editor, W3C Recommendation 10 February 2004, http://www.w3.org/TR/2004/REC-rdf-syntax-grammar-20040210/ . Latest version available at http://www.w3.org/TR/rdf-syntax-grammar/ .
[SROIQ]
The Even More Irresistible SROIQ. Ian Horrocks, Oliver Kutz, and Uli Sattler. In Proc. of the 10th Int. Conf. on Principles of Knowledge Representation and Reasoning (KR 2006). AAAI Press, 2006.
[OWL Metamodeling]
On the Properties of Metamodeling in OWL. Boris Motik. Journal of Logic and Computation, 17(4):617-637, 2007.