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Some comments on OWL Reference

From: Yuzhong Qu <yzqu@seu.edu.cn>
Date: Sat, 5 Apr 2003 22:34:51 +0800
Message-ID: <006d01c2fb80$85a0d190$300f77ca@xobjects>
To: "webont-comments" <public-webont-comments@w3.org>
Cc: "Peter F. Patel-Schneider" <pfps@research.bell-labs.com>, "Jim Hendler" <hendler@cs.umd.edu>


The OWL Reference says:
[   1.1 Purpose of this document
    The normative reference on the *PRECISE SYNTAX* of the OWL language constructs can be found in the OWL Semantics and Abstract Syntax document.
    1.3 OWL syntax 
    An OWL ontology is encoded and written as an RDF graph, which is in turn a set of RDF triples. As with any RDF graph, an OWL ontology graph can be written in many different syntactic forms (as described in the RDF/XML Syntax Specification (Revised) ...).
    1.7 Appendices to this document
    Appendix B contains an RDF schema for the OWL language constructs. ....This schema provides the *BASIS* for the RDF/XML syntax of OWL. 

The OWL S&AS says:
[2. Abstract Syntax
    (In the first paragraph.)
    ....The syntax used here is rather *Informal*, ...

The OWL Overview says:
[1.1 Document Roadmap
    The OWL Semantics and Abstract Syntax document is the *Final and Formally* stated normative definition of the language. 


It seems to me that:
1) There is no PRECISE SYNTAX  of OWL. 
2) The XML encoding of an OWL ontology is based on RDF/XML Syntax as well as RDF schema for OWL (Appendix B).
3) Without the PRECISE SYNTAX of OWL, where does the *Final and Formally* stated normative definition of the language come from?

I think that the specs should give a consistent and explicit stating on this issue.

2. The domain and range of owl:equivalentClass in OWL Lite. 

[    3.2.2 owl:equivalentClass
    NOTE: OWL DL does not put any constraints on the types of class descriptions that can be used as domain and range values of an owl:equivalentClass statement. In OWL Lite **only class identifiers and property restrictions** are allowed as domain and range values. (?)

    8.3 OWL Lite 
    the subject of owl:equivalentClass triples be named classes and the object of owl:equivalentClass triples be named classes, restrictions, or subjects of owl:intersectionOf triples (?); 

1) According to S&AS, the domain of owl:equivalentClass must be just classID.

2) As to the range of owl:equivalentClass, class identifiers and property restrictions are certainly allowed as range values. But how about others allowed as range values? What's "the subjects of owl:intersectionOf triples" mentioned in section 8.3? 

It seems most likely to be anonymous classes defined as the conjunctions of class identifiers and property restrictions. 

It (The domain and range of owl:equivalentClass in OWL Lite) should be explicitly and consistently specified.

3. RDF schema for OWL (Appendix B)

1) "rdf:resource" is a typo error as I mentioned before. It should be "rdfs:Resource".
2) The definition of owl:Thing and owl:Nothing

<Class rdf:ID="Thing">
  <unionOf rdf:parseType="Collection">
    <Class rdf:about="#Nothing"/>
      <complementOf rdf:resource="#Nothing"/>

<Class rdf:ID="Nothing">
  <complementOf rdf:resource="#Thing"/>

I suggest the axiom for owl:Thing be simplified as follows:
<Class rdf:ID="Thing">

Is there any lose of meaning?

I note owl:Nothing is not included in OWL Lite. [A note in section 3.1 Class descriptions].

Including owl:Nothing in OWL Lite will bring any harmness to OWL Lite ?

4. The rdfs:range of owl:imports

In Appendix C (OWL Quick Reference), the rdfs:range of owl:imports is missing. It should be owl:Ontology (according to Appendix B).

Yuzhong Qu
Dept.Computer Science and Engineering
Southest University, Nanjing, China
Received on Saturday, 5 April 2003 09:34:12 UTC

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