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

From: Pat Hayes <phayes@ai.uwf.edu>
Date: Fri, 12 Oct 2001 23:57:44 -0500
Message-Id: <p05101021b7ed789d5717@[205.160.76.193]>
To: Dan Brickley <danbri@w3.org>
Cc: www-rdf-rules@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,

Actually I would say not, though it's only a matter of terminology. 
It is encoded in RDF syntax, but its meaning isn't specified by 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.

Well, they can if they are DAML-savvy, but then why don't you call 
them DAML apps rather than RDF apps?

>
>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

How does the RDF application know what the DAML expressions mean? 
(Should it know about all the other extensions to RDF that havnt even 
been invented yet?)

>-- 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.

Maybe, but you can hardly pin this on DAML; *nobody* has really 
tackled this issue yet, AFAIK.

Pat
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Received on Saturday, 13 October 2001 00:57:53 GMT

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