About DENY proposal: ISSUE-73 infinite universe

Hi!

My comments to agenda item:

  o PROPOSED: close (as REJECTED) Issue 73 
    (Should owl:Thing be necessarily infinite?) 
    as per
http://lists.w3.org/Archives/Public/public-owl-wg/2008Jan/0059.html

There have already been several (strong, IMHO) arguments pro rejecting this
issue. And I will add mine, too (sorry, Jeremy! :-]):

  * The fact that owl:Thing is infinite in OWL-Full cannot really be used as
an argument for saying that owl:Thing has to be also infinite in DL.
owl:Thing in OWL-DL has a very different semantics from owl:Thing in
OWL-Full. In OWL-Full, owl:Thing is the whole universe, containing
/everything/ (including classes, properties, data values, and data types).
In OWL-DL, however, owl:Thing is only the class of individuals, but does not
contain classes, properties, data values or data types. So owl:Thing/DL and
owl:Thing/Full cannot really be compared.

  * In OWL-Full, the infiniteness is something which can be (mathematically)
concluded from the semantic properties of the language. There is no
explicitly given requirement that Full has to be infinite. So I wouldn't
like to set such an explicit requirement to DL, either.

  * And last, I do not fully agree that making DL's owl:Thing infinite
really helps in enhancing the compatibility between DL and Full. There are
certainly better characterizations of "compatibility" than via cardinality.
Very bad example, but I don't find a better at the moment: The enumeration
{1,2,3} is in some way compatible with the natural numbers |N, which is
itself in some way compatible with the real numbers |R. The compatibility
here is given by inclusion, but not by cardinality. In OWL-1.0, the
compatibility was (partially) given (hopefully) by inclusion of entailments.
The compatibility topic is a topic, which has to be further discussed, of
course. But I strongly believe that cardinality of owl:Thing will play no
real role in this discussion.


Cheers,
Michael

--
Dipl.-Inform. Michael Schneider
FZI Forschungszentrum Informatik Karlsruhe
Abtl. Information Process Engineering (IPE)
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