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RE: Extending OWL DL vocabulary (was UFDTF Metamodeling Document)

From: Conrad Bock <conrad.bock@nist.gov>
Date: Fri, 30 Nov 2007 13:59:54 -0500
To: "'Peter F. Patel-Schneider'" <pfps@research.bell-labs.com>
Cc: <public-owl-wg@w3.org>
Message-ID: <1b5801c83383$31589380$b3200681@MEL.NIST.GOV>

Peter, 

 >  > As long as we're being precise in wording, I wouldn't say 
 > > a language has metamodel facilities" if it doesn't have these
 >  > "capabilities.

 >  Which capabilities?

Subclassing owl:Class and owl:Property.

 >  > Simply making direct instances of owl:class, then instantiation
 >  > those instances is not metamodeling.  The "meta" means to to use a
 >  > language to model other languages, including by extending other
 >  > languages.

 >  Well, then OWL Full doesn't have metamodelling.  Perhaps some other
 >  term should be used, but metamodelling has been used for quite some
 >  time in KR for the ability to treat classes (and properties) as
 >  objects.

 >  > Sure, but I would claim the standard overreached.  There's no
 >  > reason for OWL to declare that all extensions of DL are not DL,
 >  > when it has no way of knowing what those extensions are.  Some of
 >  > them might well be outside DL, others not.  The tools vendors
 >  > fortunately ignored or didn't notice this overly broad restriction
 >  > in the standard.

 >  Huh?  There is indeed a need for the OWL DL recommedation to state
 >  what is in OWL DL and what is not.  If the OWL Dl recommendation
 >  doesn't say this then how is one to know how to write ontologies in
 >  OWL DL?

Agreed, but it shouldn't say something is not OWL DL with it might
actually be.  For example, suppose subclasses of owl:Class and
owl:Property were defined that introduced no restrictions or properties
at all.  This is clearly still DL.  Yet the standard says it isn't.  It
overgeneralizes about these subclasses.

 >  I'm not saying that the checking is the province of any DL reasoner.
 >  Depending on the specifics of the extension, it may be possible to
 >  employ a DL reasoner for some DL to perform the check, or it may be
 >  necessary to use a more powerful reasoner, or it may be possible to
 >  use some simpler method, or it may even be impossible to determine.

OK.

 >  Well, yes it is the responsibility of the language designer to pick
 >  a reasonable language.  However, it can easily turn out that even
 >  simple meta-level languages require complex reasoning.

Agreed, it's just that the OWL spec can't say which ones are like that
and which aren't, so shouldn't make a blanket statement about all of
them.

 >  > Where is the axiom for uml:class being a subclass of owl:class?
 >  > That would be metamodeling, see above.

 >  There is none in either OWL DL or OWL 1.1.  Why does there need to
 >  be one?  If the class has visibility on both the instance and the
 >  class level then that is metamodelling also, of a sense.

I thought that's how the vocabulary was extended.  Is there another way?
Otherwise the instances of uml:Class would not be instances of
owl:Class.

Conrad
Received on Friday, 30 November 2007 19:00:20 GMT

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