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Re: DAML Correction: Same Is Not A Sub Of Sub

From: Sean B. Palmer <sean@mysterylights.com>
Date: Sat, 5 May 2001 16:49:45 +0100
Message-ID: <006801c0d57b$03adf640$84db93c3@z5n9x1>
To: "Danny Ayers" <danny@panlanka.net>
Cc: <www-rdf-logic@w3.org>
"Danny Ayers" <mailto:danny@panlanka.net> wrote:-

> I'm still picking the bones out of this one (though I still haven't
> found the line you refer to),

Look for <Property ID="samePropertyAs"> in the DAML+OIL schema [1],
and you'll see that it has two "subPropertyOf" arcs hanging off of it.
One of them points to daml:equivalentTo, and the other one goes to
rdfs:subPropertyOf.

> since samePropertyAs is declared as a subProperty of
> subPropertyOf, while equivalentTo is not. This makes
> the meaning of samePropertyAs at least partly available
> to an RDF Schema-only agent, [...]

Unfortunately, it will also make a fully conforming RDF Schema-agent
barf due to the reasoning that I set out in my original email. The
only thing that can be gained by stating that it's a sub property of
subPropertyOf is the range and domain semantics, which should be set
out as:-

   rdf:Property rdfs:subClassOf
      [ a daml:Restriction;
        daml:onProperty daml:samePropertyAs;
        daml:toClass rdf:Property ] .

The original reasoning is that because these are the same statements:-

   :x daml:equivalentTo :y . :y daml:equivalentTo :x .

implying that:-

   daml:equivalentTo daml:inverseOf daml:equivalentTo .

And samePropertyAs is a specialization of equivalentTo, it follows
that if :y is the same property as :x, then :x is the same property as
:y. However, if you say that samePropertyAs is also a specialization
of subPropertyOf, then this implies that :y is a sub property of :x
*and* :x is a sub property of :y. According to the RDF Schema
specification, this is not permitted.

> Which I suppose is saying, the DAML schema can be
> self-consistent without having to be in the same space
> as the RDF schema.

Well, if it refers to RDF Schema terms, then it must use the semantics
of those terms. If I started using rdfs:Class as rdf:Property and vice
versa, people would soon start complaining at me. If DAML want to
point out that sub properties should be able to be sub properties of
sub properties of themselves (as long as they are equivalent), I think
they should take that up with the W3C and get them to change the
schema definition, rather than just fudging it.

This is all a consequence of my rant to SWAG-Dev about using other
people's data [2]. I think that if you have some relationship then you
always state it (unless it can be implied), but I also don't think you
should just invent new relationships that don't make sense, viz. use
other people's terms; responsibly :-)

[1] http://www.daml.org/2001/03/daml+oil#
[2] http://groups.yahoo.com/group/swag-dev/message/907

--
Kindest Regards,
Sean B. Palmer
@prefix : <http://webns.net/roughterms/> .
:Sean :hasHomepage <http://purl.org/net/sbp/> .
Received on Saturday, 5 May 2001 11:49:24 UTC

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