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Re: LANG: owl:ontology

From: Jim Hendler <hendler@cs.umd.edu>
Date: Sun, 15 Sep 2002 13:00:24 -0400
Message-Id: <p05111704b9aa6b472510@[10.0.1.2]>
To: webont <www-webont-wg@w3.org>

Some snips to save space

>From: Jim Hendler <hendler@cs.umd.edu>
>Subject: Re: Lang: owl:ontolgy
>Date: Fri, 13 Sep 2002 18:48:44 -0400
>
>>  >From: Jim Hendler <hendler@cs.umd.edu>
>>  >Subject: Re: Lang: owl:ontolgy
>>  >Date: Fri, 13 Sep 2002 14:41:31 -0400
>>  >
>>  >[...]
>>  >
>>  >>  >What happens if a class is ``claimed'' by no ontology?  What 
>>happens if it
>>  >>  >is claimed by more than one ontology?
>>  >>
>>  >>  That's easy, it is available on the web if someone wants to link to
>>  >>  it in their ontology, but it's not part of these ontologies -- i.e.
>>  >>  ontology = document is no longer true.
>>  >
>>  >What happens if it is claimed by more than one ontology?
>>
>>  so what?  Unless you assume a single universal ontology, many
>>  facts/classes may be claimed by multiple ontologies - that is why we
>>  call it the semantic Web.
>
>But what are the effects of being claimed by multiple ontologies?

That each ontology contains a pointer to this class' URI in its graph 
- and thus has whatever the semantics that that inclusion would 
assert.


>[snip]



>way we decide whether
>  > >>  carrots or potatoes are in the same ontology.
>>  >
>>  >  But everything that relates to it is probably everything on the entire
>>  >  web.  You have to say which axioms and facts you are including.  In fact,
>>  >  as RDF/XML is the exchange language, you have to say which *triples* you
>>  >  are including.
>>
>>  Yes, but we have exactly that same problem in the current system. 
>
>Not at all.  Ontologies are documents, so everything in a document is
>included.   No other determination is needed.

  It is certainly not the case in many of the examples I've seen and 
used, and even if it were the case in D+O (I don't think it is), I 
think we should fix it for owl.

>  > It
>>  is perectly legal to have a document with nothing on it but a class
>>  definition, another document that has some other class definition
>>  that points to it, and a third document that claims to be an ontology
>>  and has something which is a subclass of one of these.  That's
>>  perfectly legal, and I have a number of tools which take advantage of
>>  the fact (letting one document add properties to an ontology in
>>  another, for example). 
>
>This does nothing to determine which information to import.
>
>>  In point of fact, we could have all the
>>  triples on the ontology be in a closed list - but I don't like that -
>
>This would work, in some sense at least.  An ontology is a collection of
>triples.   But then how is this significantly different from an ontology
>being a document that is a collection of triples?

because we break the connection between a document and the collection 
of triples.  This makes it possible to have multiple ontologies in a 
single document, to compose ontologies from parts of other 
ontologies, and to merge ontologies without having to create new 
documents.  It also means that the triple store itself will contain 
the list of classes, instead of that having to be assumed from the 
document.  This means that our resolution that the graph should 
convey the ontology will be more directly met.  Also, if one 
considers that on the modern web "document" is not actually a 
terribly well-defined entity (can it be a page which is generated 
from a database, a java program, a plug-in from an ontology site?) 
then it would be nice to have something that scopes what a particular 
ontology claims, ot what I claim from it.

>  > I htink it better to have some general ideas of how the pointers
>>  work, and leave the rest unspecified for now. 
>
>Huh?  Leave the determination of which triples to import unspecified?  How
>could anyone use imports then?

All I meant was that whatever we could do for the current use of 
imports could be done with this solution as well - I didn't propose 
this as a solution to imports, but as a mechanism that will make it 
easier to implement whatever solution we determine without requiring 
a lexical (document-based) solution.

>
>>  If you want
>>  decidability/consistency, you can insist that people only use local
>  > referents or something like that.
>
>How did decidability or consistency get in here?   Decidability or
>consistency of what?
>
>>  A view of ontologies that cannot point to each other, and instances
>>  that only point to one ontology, is like the web without the links --
>>  it's still a lot of documents, but it ain't the Web.
>
>Why?  I see absolutely nothing to back up this claim.  Ontologies being
>documents and ontology documents pointing to other ontology documents sure
>looks like the Web to me!

but how do we get the pointing to?  That's the whole discussion I 
thought we were having - the DAML+OIL solution is terribly vague on 
this - and although I can live with that vagueness, it doesn't help 
the interoperability goals we have as a WG.

>[snip]



>  > >
>>  >I bring your attention to the abstract syntax document, available at
>>  >http://www.w3.org/TR/owl/ab-syn/, which includes a treatment of imports.
>>  >DAML+OIL also includes a treatment of imports.
>>
>>  yes, but we have an issue open asking for a better way to handle
>>  imports - I'm perfectly fine with going with the D+O approach (magic
>>  syntax) but the issue was raised as to whether there is a better way,
>>  and I think this is one.
>
>Sure we want a better way.  But there *is* a mechanism from DAML+OIL, and
>other proposals have already surfaced.

and mine is one of them - which is why I proposed it.

>  >
>>  >  > >>  I could include classes from other ontologies (Without 
>>importing the
>>  >>  >>  whole thing) by simply including them in my owl:ontologyDefines
>>  >>  >>  collection
>>  >>  >>     <owl:OntologyClass cyc:dog>
>>  >>  >
>>  >>  >What is the impact of this?  That cyc:dog is a resource in 
>>this ontology?
>>  >>  >That the axioms about cyc:dog (from where?) are to be included in this
>>  >  > >ontology?
>>  >>
>>  >>  yes, that the URI cyc:dog is a class, it contains class definitions,
>>  >
>>  >Classes do not contain class definitions.  Classes do not even have
>>  >really have definitions.  All there is is triples!
>>
>>  class are referred to by URIs, and are thus "indexes" into larger
>>  graphs.  Currently some people view those graphs as separable, others
>>  of us don't. Whatever the semantics would hold for the document view
>>  will hold just as easily in my view -- simply consider the ontology
>>  statement plus its defines to be what you called a document, and
>>  everything we've done to date still works just fine. 
>
>Not at all.  The problem is determining boundaries.  You haven't said where
>the boundaries between classes are supposed to be, so you haven't produced
>a viable proposal for imports.

well, I'm not real fond of boundaries personally, but I still don't 
see why mine had any less boundaries than anyone else's.


>[snip]


>  > >>  >
>>  >>  >Again, which aspects of cat are part of Pets and which are 
>>part of Felines?
>>  >>
>>  >>  all of each are part of both
>>  >
>>  >What all?  Do you mean all RDF triples currently on the web that mention
>>  >cat?  Do you mean the intended meaning of whoever wrote the document that
>>  >the URI points to?
>>

of course not!!  URI1:cat is in no way the same as URI2:cat unless 
someone comes along and states their equivalence.  And I can't know 
the intended meaning of someone else - so I will assume that the 
owl:ontologyDefines list is the same sort of "closure" that you are 
assuming a document is, but I don't need to insist that it ever 
appear as a document - which is an improvement.

>  > whatever solution you would use for DAML+OIL works for this as well
>
>Sure, the solution in DAML+OIL is to identify ontologies as certain kinds
>of documents.

I am not convinced this is true, and if it is, I'm still not 
convinced it's a good idea - which is why we have a working group to 
discuss such things in.

-- 
Professor James Hendler				  hendler@cs.umd.edu
Director, Semantic Web and Agent Technologies	  301-405-2696
Maryland Information and Network Dynamics Lab.	  301-405-6707 (Fax)
Univ of Maryland, College Park, MD 20742	  240-731-3822 (Cell)
http://www.cs.umd.edu/users/hendler
Received on Sunday, 15 September 2002 13:00:34 GMT

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