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Re: requirement: rdfs query (for lack of a better name...)

From: Pat Hayes <phayes@ihmc.us>
Date: Fri, 7 May 2004 13:50:09 -0500
Message-Id: <p06001f28bcc1760e081a@[10.0.100.76]>
To: Kendall Clark <kendall@monkeyfist.com>
Cc: RDF Data Access Working Group <public-rdf-dawg@w3.org>

>Requirement
>-----------
>It should be possible to query the RDFS structure of an RDF graph to find,
>for example, the parents and instances of a class or the class tree.
>
>Discussion
>----------
>I'm not sure whether this comes down, in the end, to a semantic requirement
>or just a request for sugar for a particular kind of query; but what my
>users need (and we have implemented in a really ugly, API munging way) is
>the ability to ask for all the instances of a class,

Query:
[??x rdf:type ex:TheClass .]

(using ?? to flag a must-bind) should get you all the instances that 
are listed in the graph. Whether that is ALL instances is another 
matter altogether:I don't think that it makes sense to ask that as an 
RDF query.

>  all the parents

?Superclasses? If so,

Query:
[ex:TheClass rdfs:subClassOf ??x]

should work, but what you get will certainly not be *all* of them. 
You might be unpleasantly surprised by how many of them there are, 
even if the set of all of them was computable.

Pat


>of a
>class, and so on. Being able to do these queries, and being able to do them
>"easily" (yes, I know, untestable, but still...) is a real requirement for us.
>
>The DIG Description Logic Interface ASK language is, more or less, what we'd
>like to have. See <http://dl-web.man.ac.uk/dig/>.
>
>Best,
>Kendall Clark


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Received on Friday, 7 May 2004 14:50:11 GMT

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