|I have a few (mostly minor/editorial) comments on the December 2 drafts:
An overall editorial comment/request: - Could you create HTML anchors for all definitions in the documents? I would like to be able to link directly to definitions of, e.g., datatype maps and vocabularies.
- the definition of datatypes in section 4 lacks the lexical-to-value and facet-to-value mappings [these are clearly part of the datatype] - for the datatypes you rely on XML Schema 1.1 datatypes, and you seem to have included most of them that make sense. But you have not included precisionDecimal. Is there a rationale for that? - the difference in your definition of the value spaces of hexBinary and base64Binary (i.e., non-disjoint) and the definition of XML schema (i.e., disjoint) should be pointed out in the document, as you did for the numeric types - I strongly suggest you use the PNG format for the images in the document, rather than GIF. I suspect this is even W3C policy.
- Some definitions are difficult to read, because they rely on terms defined in another document. When referring to a term defined in another document (e.g., the syntax specification), could you include a direct link and a reference (e.g., [OWL-Syntax])? I think this would help the reader. - why a new definition for datatype maps? Why not use the same one as in RDF and OWL 1? The definition of interpretation would become a little bit more complex, but I don't really see that as a problem. - in the definition of interpretation, using "Int" for the object domain is rather unfortunate, because it could be confused with the set of integers. I would suggest "Obj" or "I". - first sentence of section 2.3: the definition of satisfaction should explicitly refer to the tables that contain the conditions of satisfaction. "Appropriate conditions" is not sufficient. - I could not find the definition of the term "axiom closure". It is used in several places. - section 2.3: we have separate subsections for the different tables? Each subsection only contains one sentence in the table, and the sentences are very much alike. One could simply write one sentence and refer to all tables, and get rid of the subsection headings. - in section 2.3.6, the comment in the parentheses about renaming anonymous individuals should be made part of the definition, i.e., should not appear in parentheses. - in section 2.5, "variable" is not defined. - paragraph before section 4, first sentence: "is is" => "is" - it is probably a good idea to refer to the second edition of description logic
- in OWL 2 RL I do not understand why the following features are not included -- they are easily implemented the rules:
- in section 6, I could not find the "productions defining the general concepts of the language". could you include a direct link? - section 6.1 and 6.3: "subObjectPropertyExpressions" => "subObjectPropertyExpression"
- if there are differences between the datatypes and facets in tables 2.2 and 2.3, on the one hand, and the datatypes and facets in that syntax specification, these should be mentioned. If there are no differences, this fact should be mentioned as well. - in my opinion, this document should use exactly the same definition of datatype map as the direct semantics specification. - above definition 4.2: "a OWL" => "an OWL" - I do not understand the purpose of section 6. There are no notions of consistency or entailment that could be implemented, so I don't see how anyone could exploit theorem 6.1.
PeterPatel-Schneider 00:30, 12 March 2009 (UTC)
[Draft Response for LC Comment 21] JDB2
Thank you for your message <http://lists.w3.org/Archives/Public/public-owl-comments/2009Jan/0024.html> on the OWL 2 Web Ontology Language last call drafts.
Anchors have been added in many places, feel free to ask for more, as adding anchors changes neither the form nor the meaning of the documents. The general form of the anchors are def_<term_with_underscores>, but this was not feasible in all cases. The documents provide anchors for each section which can also be used in other documents.
Diffs are not provided here for all changes, as the addition of anchors may have been interspersed with other work on the documents.
Initial diffs for Direct Semantics can be found at: http://www.w3.org/2007/OWL/wiki/index.php?title=Direct_Semantics&diff=17912&old$ Initial diffs for Syntax can be found at: http://www.w3.org/2007/OWL/wiki/index.php?title=Syntax&diff=17910&oldid=17665
Structural Specification and Functional Syntax document:
The discussion of datatype maps in Section 4 of the Specification document is not a formal one, it concentrates on those parts of datatype maps that are needed for the syntax, deferring formal discussion to Section 2 of the Direct Semantics document. It is thus appropriate that Section 4 of the Syntax document does not explicitly call out the semantic mappings that are part of datatype maps, only alluding to their presence.
The precisionDecimal datatype of XML Schema perhaps could have been included in OWL 2. However, the definition of equality and order on precisionDecimal does not appear to be what would be desired in a representational setting (which would instead be based on viewing elements of the datatype as ranges of numbers).
Due to several comments and implementation experience, hexBinary and base64Binary now have disjoint value spaces, so there is no difference from XML Schema. This is a change to OWL 2.
The OWL WG agrees that PNG would be preferable to GIF. The WG expects to convert the GIF figures to PNG at the time of next publication.
Direct Semantics document:
Full linking from the Direct Semantics is a major task, which would, for example, include linking syntax. Links have been added in the Vocabulary section. The diffs are http://www.w3.org/2007/OWL/wiki/index.php?title=Direct_Semantics&diff=17913&old$
The definition for datatype maps in Direct Semantics extends datatype maps from RDF Semantics, in particular for facets.
The wording "satisfies appropriate conditions listed in the following sections" in Section 2.3 has been changed to "satisfies the condition in the tables below for the axiom". The diffs are http://www.w3.org/2007/OWL/wiki/index.php?title=Direct_Semantics&diff=17914&old$
Axiom closure is defined in Syntax. A link to the definition has been added where the term is used. The diffs are http://www.w3.org/2007/OWL/wiki/index.php?title=Direct_Semantics&diff=17915&old$
If the document was being rewritten from scratch, the subsections of section 2.3 might not be needed, but they seem to be innocuous and will stay for now.
The definition of axiom closure from Syntax includes "renaming apart" so the parentheses in 2.3.6 are appropriate.
Section 2.5 now includes a standard definition for variables and the definition of Boolean Query Answering notes that quantification needs to be considered. The diffs are http://www.w3.org/2007/OWL/wiki/index.php?title=Direct_Semantics&diff=17918&old$
In Section 3 "is is" has been replaced by "is". No diffs are available for this interesting change.
The second edition of the DL handbook is now referenced. Again no diffs are available for this useful change.
"I" is uniformly used as a signal for an interpretation, instead of sometimes Int and sometimes I. The diffs are http://www.w3.org/2007/OWL/wiki/index.php?title=Direct_Semantics&diff=17932&old$
The above changes are all editorial.
As stated in the document, OWL 2 RL is designed for easy and efficient implementation using existing forward-chaining rule systems. Adding owl:Thing or reflexive object properties needs rules that operate over all individuals, which goes against efficiency, and may not even be possible in some rule systems. Similarly, most rule systems are designed for positive ground facts which dictates against allowing negative property assertions.
The phrase "General concepts of the language" has been replaced by an explicit pointer to Section 13.1 of Syntax. This change was done in two phases: http://www.w3.org/2007/OWL/wiki/index.php?title=Profiles&diff=prev&oldid=19186 and http://www.w3.org/2007/OWL/wiki/index.php?title=Profiles&diff=19552&oldid=19193
The non-terminal subObjectPropertyExpressions is used uniformly throughout the document set, but it really should be subObjectPropertyExpression. This is only a change to a non-terminal in the grammar, which is an editorial change. The diffs are: http://www.w3.org/2007/OWL/wiki/index.php?title=Profiles&diff=18708&oldid=18687 http://www.w3.org/2007/OWL/wiki/index.php?title=Syntax&diff=18707&oldid=18533
The above changes are all editorial.
RDF-Based Semantics document:
As a general note, please be aware that the RDF-Based Semantics is not yet a Last Call working draft, and it has received considerable editing since the last publication in December.
It is indeed intended to have the same set of datatypes and facets in the RDF-Based Semantics spec as in the Structural Specification. The working group agrees that this should be more explicitly stated, since it does not easily follow from the text in the published working draft. Therefore, the working group plans to add clarifying text in the next published working draft.
Concerning the definition of datatype maps: Note that the OWL 2 RDF-Based Semantics aims for full compatibility with the semantics defined in the RDF Semantics specification. The semantics there already provides notions of datatypes and datatype maps, and defines certain semantic conditions for them. In particular, as for OWL 1 Full, the central definition of an OWL 2 Full interpretation provided in the RDF-Based Semantics document builds on top of the definition of a so called "D-interpretation", as defined in the RDF Semantics specification, and by this the existing definitions of datatypes and datatype maps from the RDF Semantics specification are reused.
Further, since OWL 2 provides for the new concept of datatype facets, the definition of a datatype, as given in the RDF Semantics specification, has been extended by the notion of a facet space. Extending the definition of a datatype is explicitly permitted by Section 5.1 of the RDF Semantics specification.
Nevertheless, it is true that the different concepts used in the definition of the extension for facets did not well match the concepts used in the Direct Semantics specification in the last published working draft. This is currently under revision, and the final outcome will be that the different concepts are compatible with each other in that the different notions of datatype maps can be easily transformed in each other.
Thank you for pointing out the typographical error "an OWL", it will be fixed in the next publication.
The purpose of Section 6 of the RDF Semantics is to show how the two semantics of OWL 2, the RDF-Based Semantics and the Direct Semantics, relate to each other. There is corresponding material in the OWL 1 recommendations. Be informed that at the time of the last publication, this section was in a very early and incomplete state. A final and much enhanced version of this section is planned for the next publication.
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Regards, Peter F. Patel-Schneider Michael Schneider on behalf of the W3C OWL Working Group