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Re: Case for Reinstatement of Qualified Cardinality Restrictions

From: Jeff Heflin <heflin@cse.lehigh.edu>
Date: Thu, 24 Apr 2003 15:46:04 -0400
Message-ID: <3EA83EFC.23EC26CC@cse.lehigh.edu>
To: "Peter F. Patel-Schneider" <pfps@research.bell-labs.com>
CC: www-webont-wg@w3.org

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>

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.

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? 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?

Help, I think my brain is about to explode. :-(

Jeff

"Peter F. Patel-Schneider" wrote:
> 
> From: Jeff Heflin <heflin@cse.lehigh.edu>
> Subject: Re: Case for Reinstatement of Qualified Cardinality Restrictions
> Date: Wed, 23 Apr 2003 14:29:15 -0400
> 
> > Peter,
> >
> > Guus's comment got me thinking. My original message was based on what
> > was true for DAML+OIL, and I just assumed it wasn't changed in OWL
> > because I didn't remember it coming up as an issue. However, I started
> > poking around in the AS&S section 4, and don't see a transformation from
> > the abstract syntax that would produce a piece of RDF syntax in which an
> > owl:Restriction had a combination of owl:cardinality, owl:allValuesFrom,
> > owl:someValuesFrom, etc. The only way this could happen is if different
> > restrictions could have the same main node, but I'm assuming that the
> > "_:x" notation means a blank node, which you say must be local to each
> > transformation. If the RDF syntax of OWL is only those RDF graphs that
> > can be produced from abtract OWL ontologies by applying the
> > transformation rules, then it seems that Guus is right (if I'm wrong
> > please point out how the transformation can be performed or where my
> > assumptions went astray).
> 
> I don't see such a transformation.  There is abstract syntax of the form
>         restriction(foo cardinality(5) allValuesFrom(bar))
> but this translates into an intersection.
> 
> > In any case, this exercise has led me to believe we need to do two
> > things with the OWL specs. First, I think the reference needs to discuss
> > what is the preferred way for writing multiple restrictions on a single
> > property (I assume this is as an intersectionOf Restrictions, although
> > this is very ugly, and I much prefer the syntax used in my previous
> > message, if it's legal and correct OWL).
> 
> The only reasonable way to write multiple restrictions on a single property
> in the RDF encoding is with an intersection.  It would have been nice to
> not have to do this, but our hands were tied.
> 
> > Second, although the AS&S makes it easy to transform from the abstract
> > syntax to RDF, I think it is much harder to do the reverse
> > transformation (which actually seems like a more common one). I think it
> > would be nice to have a table that presents this transformation. This
> > may also be useful in placating people who ask "where's the official
> > syntax?"
> 
> There is a proposal for such a reverse translation from Jeremy.
> 
> > Jeff
Received on Thursday, 24 April 2003 15:46:15 GMT

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