LC Responses/SWD1

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To: SWD WG <public-swd-wg@w3.org>, Guus Schreiber <schreiber@cs.vu.nl>
CC: public-owl-comments@w3.org
Subject: [LC response] To Guus Schreiber

Dear Guus,

Thank you for your comment
     <http://lists.w3.org/Archives/Public/public-owl-comments/2009Feb/0012.html>
on the OWL 2 Web Ontology Language last call drafts.

OWL 2 is a successor of OWL and not only a successor of OWL DL. You are right, however, in pointing out that this is not made sufficiently clear in some documents, and that they sometimes seem to suggest that this is not the case.

In order to address this problem the WG has added a Document Overview and has revised several of the other documents. The Document Overview provides a high level view of the design, making it clear that OWL 2 refers to the language as a whole, that an OWL 2 ontology can be equivalently seen as an RDF graph or as an abstract structure (an instance of the ontology class), and that ontologies can be interpreted using either the RDF-Based semantics or the Direct semantics (see our response to Frank van Harmelen [1] for more on this topic).

Regarding the presentation of the material, the Structural Specification and Functional-Style Syntax document, which is the core reference for language features and usage, has been revised so that the features are illustrated using examples in both functional and triple based syntaxes. The New Features and Rationale document is not intended as a language reference, but documents the rationale for the new features of OWL 2. In order to keep the document short only the more compact functional syntax is provided. This document is, however, not yet at last call, and so is still subject to change.

Regarding the RDF/XML exchange syntax being the normative exchange syntax, this is now more clearly emphasised. E.g., the new Document Overview [2] explicitly states that "The primary exchange syntax for OWL 2 is RDF/XML [RDF Syntax]; this is indeed the only syntax that must be supported by all OWL 2 tools (see Section 2.1 of the OWL 2 Conformance document [OWL 2 Conformance])." The message is repeated elsewhere, e.g., in the Conformance and Test Cases document [3], where it says that "conformant OWL 2 tools that take ontology documents as input(s) MUST accept ontology documents using the RDF/XML serialization [OWL 2 Mapping to RDF Graphs], and conformant OWL 2 tools that publish ontology documents MUST be able to publish them in the RDF/XML serialization if asked to do so".

We are grateful for your supportive comments regarding some of the new features of OWL 2, and we hope that the changes we have made address your concerns about the presentation.

[1] http://lists.w3.org/Archives/Public/public-owl-comments/2009Mar/0049.html
[2] http://www.w3.org/2007/OWL/wiki/Document_Overview
[3] http://www.w3.org/2007/OWL/wiki/Conformance_and_Test_Cases

Please acknowledge receipt of this email to <mailto:public-owl-comments@w3.org> (replying to this email should suffice). In your acknowledgment please let us know whether or not you are satisfied with the working group's response to your comment.

Regards,
Ian Horrocks
on behalf of the W3C OWL Working Group



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The Semantic Web Deployment (SWD) Working Group has reviewed the

OWL2 Last Call documents. We apologise that these comments are provided to you after the deadline. We hope you will still be able to consider them.

NOTE: Our comments are given from the perspective of the work of SWD on SKOS [1], as SKOS is based on RDF/OWL.


1. The SWD WG notes that some of the extensions provided by OWL2 appear to be useful for SKOS. For example, property disjointness can be used in specifying the semantics for SKOS mapping relations. Although currently not needed in the SKOS semantics, we can foresee use cases for new property characteristics such as (a)reflexivity and asymmetry, e.g. for specifying application-specific specializations of SKOS semantic relations. For alignment between SKOS and OWL DL the possibility to define axioms about annotation properties is perceived as useful.


2. The SWD WG is disappointed about the way the OWL2 material is presented, in particular the lack of using either an RDF/XML or an RDF triple representation of OWL2. Even the " New Features and Rationale" document [2] refrains from using such syntax. This makes the OWL2 documents inaccessible for the typical SKOS user. We request that the OWL WG remedies this situation.


3. The SWD WG notes that most OWL2 documents give the impression that OWL2 is just an extension of OWL1 DL, and not of OWL1 Full. For example, the introduction of OWL2 Direct Semantics document states [3]:

  [[
    Since OWL 2 is an extension of OWL DL
  ]]

Only one document clearly makes the OWL2 DL and OWL2 Full distinction [4]. In our experience OWL Full is the dominant OWL usage pattern for SKOS. We therefore request that the OWL2 document are edited in such a way that whenever the term "OWL2" is used, it is used to refer to the OWL2 language as a whole (OWL2 DL and OWL2 Full). If OWL2 DL is meant, it should be explicitly marked as such. We also request that the nature and role of OWL2 Full are clearly stated in other central OWL documents, not just in [4].


We hope these comments are useful for you.

Best, Guus Schreiber on behalf of the Semantic Web Deployment Working Group

[1] http://www.w3.org/TR/skos-reference/
[2] http://www.w3.org/TR/2008/WD-owl2-quick-reference-20081202/
[3] http://www.w3.org/TR/2008/WD-owl2-semantics-20081202/#Introduction
[5] http://www.w3.org/TR/2008/WD-owl2-rdf-based-semantics-20081202/