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Re: Case for Reinstatement of Qualified Cardinality Restrictions

From: Jeff Heflin <heflin@cse.lehigh.edu>
Date: Fri, 25 Apr 2003 17:37:07 -0400
Message-ID: <3EA9AA83.F1526FC9@cse.lehigh.edu>
To: "Peter F. Patel-Schneider" <pfps@research.bell-labs.com>
CC: www-webont-wg@w3.org

Thanks for the response, Peter. I think I'm begining to get this
straight. I understand your point about the restrictions having the same
extensions, but it's a subtle point and took working through an example
to see. I may send a message to the WG later showing this, in case
anyone else had the same confusion I did. Anyway, if I understand
correctly 

<owl:Restriction>
  <owl:onProperty rdf:resource="&eg;hasDigit"/>
  <owl:cardinality rdf:datatype="&xsd;int">5</owl:cardinality>
  <owl:allValuesFrom rdf:resource="&eg;Digit" />
  <owl:someValuesFrom rdf:resource="&eg;Finger" />
</owl:Restriction>

is illegal in an OWL DL Ontology (because there is no transformation
from the abstract syntax to it), but is okay syntactically in an OWL
Full ontology (since it's legal RDF). However, the RDF compatible
semantics gives you an undesired interpretation if you try such a thing
in OWL Full, so you should really avoid it.

I think some of my other confusions could be elliminated by a few
well-placed clarification in S&AS. If I had read it from cover to cover,
I might have picked up on the points below, but I jumped straight to the
sections that I thought had the answers I was looking for, and this is
where I went astray.

I suggest the following additions to S&AS:

- In Section 4 (Mapping to RDF Graphs), at the outset remind readers
that the abstract syntax only applies to OWL Lite and OWL DL, and thus
the transformations described constrain the syntax of these, but not OWL
Full.

- In Section 5 (RDF-Compatible Model-Theoretic Semantics), mention in
the beginning that this is the ONLY semantics for OWL Full, but that the
semantics also apply to OWL DL

- In fact, it may be helpful to readers who are looking for specific
material if you made some of the section headings more specific. For
example:
2. Abstract Syntax => 2. Abstract Syntax for OWL Lite and OWL DL
3. Direct Model-Theoretic Semantics => 3. Direct Model-Theoretic
Semantics for OWL Lite and OWL DL
4. Mapping to RDF Graphs => 4. Mapping the Abstract Syntax to RDF Graphs
5. RDF-Compatible Model-Theoretic Semantics => 5. RDF-Compatible
Model-Theoretic Semantics for OWL Full and OWL DL

With these changes, a reader interested in one of the three sublanguages
should have no trouble finding the sections that are of interest to
him/her.

Jeff

"Peter F. Patel-Schneider" wrote:
> 
> From: Jeff Heflin <heflin@cse.lehigh.edu>
> Subject: Re: Case for Reinstatement of Qualified Cardinality Restrictions
> Date: Thu, 24 Apr 2003 15:46:04 -0400
> 
> > Sorry, this issue keeps nagging at me...
> >
> > I looked at Sect. 5 of S&AS (RDF-compatible semantics) and it seems that
> > it gives semantics to Restriction resources that have some combination
> > of cardinality, someValuesFrom and allValuesFrom properties, such as in
> > the example below.
> >
> > <owl:Restriction>
> >   <owl:onProperty rdf:resource="&eg;hasDigit"/>
> >   <owl:cardinality rdf:datatype="&xsd;int">5</owl:cardinality>
> >   <owl:allValuesFrom rdf:resource="&eg;Digit" />
> >   <owl:someValuesFrom rdf:resource="&eg;Finger" />
> > </owl:Restriction>
> >
> > Furthermore, it looks like the semantics would be the same as if you had
> > an intersection of:
> >
> > <owl:Restriction>
> >   <owl:onProperty rdf:resource="&eg;hasDigit"/>
> >   <owl:cardinality rdf:datatype="&xsd;int">5</owl:cardinality>
> > </owl:Restriction>
> >
> > <owl:Restriction>
> >   <owl:onProperty rdf:resource="&eg;hasDigit"/>
> >   <owl:allValuesFrom rdf:resource="&eg;Digit" />
> > </owl:Restriction>
> >
> > <owl:Restriction>
> >   <owl:onProperty rdf:resource="&eg;hasDigit"/>
> >   <owl:someValuesFrom rdf:resource="&eg;Finger" />
> > </owl:Restriction>
> 
> No.  It is different.  The first implies that the extension of the three
> just above are all the same.
> 
> > The reason is that in the section called "Conditions on OWL
> > restrictions" the semantics for each of these types of restrictions only
> > depends on having two triples (onProperty and something else) with the
> > same subject, and these conditions are met in the "jumbo restriction"
> > above.
> >
> > However, this seems to contradict Section 4 (Mapping to RDF Graphs)
> > which does not provide a translation into the "jumbo restriction" and
> > therefore implies that it doesn't have semantics, and also isn't even
> > valid syntax.
> 
> No, all that this indicates is that the first is not in OWL DL.
> 
> > This is very confusing. I thought the mapping to RDF defined the RDF
> > syntax, but that doesn't seem to be the case.  Does it just define the
> > syntax for OWL DL, and not OWL Full?
> 
> The mapping to RDF defines the syntax for OWL DL and OWL Lite.
> 
> > Even if this was the case, it would
> > seem that the RDF combatible semantics and the abstract semantics
> > disagree on what constitutes an OWL DL graph (take this Restriction case
> > as an example). Is it the case that the RDF compatible semantics only
> > apply to some subset of RDF graphs as determined by the transformation
> > in Section 4?
> 
> The RDF-compatible smenatics applies for all RDF graphs.
> 
> > Help, I think my brain is about to explode. :-(
> 
> Welcome to the wonderful world of triples.  :-)
> 
> > Jeff
> 
> peter
Received on Friday, 25 April 2003 17:37:12 GMT

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