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Re: matching existing existentials in the consequent.

From: Dan Connolly <connolly@w3.org>
Date: Fri, 18 Apr 2008 17:31:38 -0500
To: public-cwm-talk@w3.org, Jeff Thompson <jeff@thefirst.org>
Message-Id: <1208557898.4651.89.camel@pav.lan>

> However, bob already owns Fluffy who is a Cat, but cwm seems to ignore
this and asserts that
> he owns another Cat:
> :bob a :CatLover; :owns :fluffy, [a :Cat].

Well, cwm isn't saying whether [a :Cat] is the same cat
as :fluffy or not.

> I ask because cwm will match existing existentials in the antecedent, so shouldn't
> it also match them in the consequent, and just leave it as bob owns Fluffy without
> adding another assertion?

Perhaps... cwm does some redundancy checking, but it's
not smart enough to realize that

 :bob :owns [a :Cat]

is redundant w.r.t.

 :bob :owns :fluffy. :fluffy a :Cat.

The problem of figuring out which part of the conclusion is
redundant is pretty hard. It's called the subgraph isomorphism
problem, I gather.

See also discussion of "leaning".

http://www.w3.org/TR/2004/REC-rdf-mt-20040210/#deflean
http://www.w3.org/2001/sw/DataAccess/issues#rdfSemantics


-- 
Dan Connolly, W3C http://www.w3.org/People/Connolly/
gpg D3C2 887B 0F92 6005 C541  0875 0F91 96DE 6E52 C29E
Received on Friday, 18 April 2008 22:32:08 GMT

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