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query and unification

From: Graham Klyne <GK@NineByNine.org>
Date: Tue, 03 Jul 2001 14:08:51 +0100
Message-Id: <>
To: jos.deroo.jd@belgium.agfa.com
Cc: fmanola@mitre.org, connolly@w3.org, phayes@ai.uwf.edu, w3c-rdfcore-wg@w3.org
Hmmm...  my take is that querying is asymmetric, but unification is symmetric:

   (query Q D) != (query D Q)


   (unify E1 E2) == (unify E2 E1)

Maybe query is a special case of unification in which only one expression 
contains a variable to be substituted?


At 01:08 AM 6/30/01 +0100, jos.deroo.jd@belgium.agfa.com wrote:

>that query thing is an interesting idea!
>when we try to unify 2 anonymous nodes it is actually
>like a query of one node against the other node
>(the latter node looking like an in-line set of statements)
>so the former one is existentially quantified
>whereas the latter one is universally quantified
>(and subjects match immediately (we use null's for them))
>and so everybody is right
>Jos De Roo, AGFA http://www.agfa.com/w3c/jdroo/
Received on Tuesday, 3 July 2001 09:34:55 UTC

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