LC3 Responses/DB7

To: daniel@fgm.com
CC: public-owl-comments@w3.org
Subject: [LC response] To Daniel Barclay

Dear Daniel,

Thank you for your comment
     <http://lists.w3.org/Archives/Public/public-owl-comments/2009Sep/0011.html>
on the OWL 2 Web Ontology Language last call drafts.

In the relevant UML definition an enumeration of individuals is associated with a set of individuals. The definition of structural equivalence is based on the equivalence of these sets. As discussed in Section 2.1 [1], sets written in a concrete syntax (such as the functional syntax) are not necessarily expected to be duplicate free, but duplicates should (in the RFC 2119 sense) be eliminated when ontology documents written in such syntaxes are converted into instances of the UML classes of the structural specification, i.e., during parsing.

The wording you mention is not part of the formal definition of enumerations of individuals but is intended to provide an informal and intuitive explanation of the meaning of this piece of syntax. We were aware of the possible confusion between UML classes/instances and ontology classes/instances and were careful to ensure that we explicitly say "UML Class" or "instance of UML Class" whenever we are referring to the former. We now explicitly mention this, as well as clarifying some other issues related to the use of UML, in Section 2.1 [1]. To review these changes please refer to the relevant diff [2].

[1] http://www.w3.org/2007/OWL/wiki/Syntax#Structural_Specification

[2] http://www.w3.org/2007/OWL/wiki/index.php?title=Syntax&diff=25572&oldid=25485

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

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Section 8.1.4, Enumeration of Individuals, says:

   An enumeration of individuals ObjectOneOf( a1 ... an )
   contains exactly the individuals ai with 1 ≤ i ≤ n.

Is that wording sufficient to specify whether a ObjectOneOf
construct that lists N Individual constructs (strings matching the
Individual non-terminal) implies that the enumerated set contains
N individuals or just implies that the set contains the N or fewer
individuals denoted by the N Individual constructs (e.g., if the
same IRI is specified twice (either with the exact same IRI
non-terminal or two different IRI non-terminals that represent the
same IRI))?

(I can't quite tell.  I don't yet know the structural equivalence
rules, to know whether they resolve that apparent ambiguity.

Also, it's not always clear when words like "individual" and "class"
refer to the structural objects (those given in UML) that
represent descriptions of individuals and classes, etc., vs. when
they refer to the described individuals and classes themselves
(which I would think would at least partly be left for the semantic
specifications (thinking of owl:sameAs)).)