Re: Extending OWL DL vocabulary

From: "Conrad Bock" <>
Subject: RE: Extending OWL DL vocabulary (was UFDTF Metamodeling Document)
Date: Fri, 30 Nov 2007 13:59:54 -0500

> 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.

Why?  What is special about these abilities?  What can be done with
these abilities that cannot be done with the facilities in OWL 1.1?

>  >  > 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.

Huh?  OWL DL is a particular language.  There is no claim that OWL DL is
the largest possible language that fits within the DL paradigm.  In any
case, standard DLs don't even have the notion of the class of all
classes or the class of all properties, so even just taking about them
takes one out of the generally-accepted DL paradigm.  Given all this, I
don't see what support there is for your claim.

>  >  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.

Huh?  The OWL DL spec doesn't say anything about the difficulty of
reasoning with metaclasses.  How can it, as it doesn't say anything
about metaclasses at all?  The OWL Full spec also doesn't say anything
about the difficulty of reasoning with metaclasses either, by the way.

>  >  > 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.

I don't understand what you mean by extending a vocabulary.  

> Conrad

Peter F. Patel-Schneider
Bell Labs Research

Received on Saturday, 1 December 2007 14:15:58 UTC