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Re: Expressiveness of RDF as Rule Conclusion Language (was Re: W hat is an RDF Query? )

From: Dan Brickley <danbri@w3.org>
Date: Fri, 12 Oct 2001 16:12:10 -0400 (EDT)
To: "Peter F. Patel-Schneider" <pfps@research.bell-labs.com>
cc: <phayes@ai.uwf.edu>, <seth@robustai.net>, <www-rdf-rules@w3.org>
Message-ID: <Pine.LNX.4.30.0110121558210.8392-100000@tux.w3.org>

On Fri, 12 Oct 2001, Peter F. Patel-Schneider wrote:

> And just how are RDF applications supposed to determine when to do this
> merging?
>
> peter

By using all that DAML+OIL good stuff you've been slaving over, of
course :)

All DAML+OIL instance data is RDF, and RDF apps that are built
to know about even a subset of DAML+OIL can make good use of that when
doing data merging.

For eg., consider the property http://xmlns.com/foaf/0.1/mbox
from the namespace http://xmlns.com/foaf/0.1/

	[[
	FOAF is expressed as an RDF Schema, annotated with DAML to express the
	fact that a foaf:mbox uniquely picks out an individual.
	]]

Excerpting from that schema:

      <rdf:Property rdf:about="http://xmlns.com/foaf/0.1/mbox"
	rdfs:label="Personal Mailbox"
	rdfs:comment="A web-identifiable Internet mailbox associated with  exactly one owner.
	This property is a 'unique property' in the DAML+OIL sense, in  that
 	there is at most one individual that has any particular personal
	mailbox.">

	<rdfs:domain rdf:resource="http://xmlns.com/foaf/0.1/Person" />
	<rdfs:range  rdf:resource="http://www.w3.org/2000/01/rdf-schema#Resource" />
 	<rdf:type  rdf:resource="http://www.daml.org/2001/03/daml+oil#UnambiguousProperty"/>
        <rdfs:isDefinedBy rdf:resource="http://xmlns.com/foaf/0.1/" />
       </rdf:Property>

Since we say the property is of type http://www.daml.org/2001/03/daml+oil#UnambiguousProperty
we can use this knowledge in RDF-based applications -- for example merging
blank nodes where each node has a property with the exact same resource as
its value. In this example, merging nodes that stand for the individual
whose presonal mailbox is mailto:foo@example.com, perhaps.

Aside: I could complain here that DAML+OIL gives us no mechanism for guaranteeing
that the at-most-one-ness remains static in the face of time and change,
but that's probably a can of worms best opened in a separate thread.
DAML+OIL's "worldview" isn't one that explicitly acknowledges time and
change, and there are good reasons for this being the case. How this
relates to the need to deploy DAML+OIL ontologies in the Web is something
that looms rapidly, imho.

Dan


> > yOn Fri, 12 Oct 2001, Pat Hayes wrote:
> >
> > > The graph-merging rules described in section 3 of the RDF MT document
> > > should make this clear: if you merge two RDF graphs then you *must*
> > > merge nodes with the same URI, but you *must not* merge blank nodes.
> >
> > ...though in practice RDF applications are free to additionally
> > do some extra merging, if they have for some other reason to infer that
> > the nodes refer to some common entity. Right? (ie. the
> > graph-merging rule is just one thing that realworld RDF apps will do when
> > they're merging data from multiple sources)
> >
> > Dan
> >
> >
>
Received on Friday, 12 October 2001 16:12:28 GMT

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