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Re: What is an RDF Query?

From: Eric Prud'hommeaux <eric@w3.org>
Date: Fri, 14 Sep 2001 10:55:09 -0400
To: David Allsopp <d.allsopp@signal.QinetiQ.com>
Cc: www-rdf-rules@w3.org
Message-ID: <20010914105509.A26008@w3.org>
On Fri, Sep 14, 2001 at 08:48:26AM +0100, David Allsopp wrote:
> 
> 
> Eric Prud'hommeaux wrote:
> 
> > Be they in the original dataset or in temporary database from which
> > the query response is culled, the consequence of a rule must be noted
> > in order to be useful. I called that operation "inserting", perhaps
> > wrongly (or incoherently). By the terms I used,
> >   if P then Q
> > can be described as a rule made of a query P and an assertion Q.
> 
> 
> > > No, nobody's saying one should match a _rule_ against a _query_, I
> > > think.
> > >
> > > As Pat says, the antecedent of a rule matches assertions. I think some
> > > people regard the antecedent as a query over the fact base ("Is this
> > > assertion in the fact base? If so, assert the consequent").
> > 
> > I meant the query and assertion to be tied together. I state a rule in
> > terms of a query and set of assertions.
> 
> Yes; I think we are vigorously agreeing 8-)
> 
> > > In implementation terms, the antecedent may literally involve a query,
> > > because to match it against an assertion one has to extract assertions
> > > from a fact base (i.e. query a database looking for matching
> > > assertions). One might then speak of "matching the query" i.e.
> > > succeeding in matching the rule's antecedent with an assertion.  I think
> > > this is common (though clearly confusing) usage...
> > 
> > I think the reason it is/could be useful is that the query part of
> > rules can be expressed in the same language as the query part of
> > queries (which would be the greater part).
> 
> Yes, good point.
> 
> > > Perhaps the confusion lies in "query" as an expression (where some
> > > syntax, such as a question mark, indicates a question), and "query" as a
> > > implicit process, where assertions are compared.
> > 
> > Is there a difference beyond the expectation of what to do with the
> > results?
> 
> Not really, but it seems to be leading to confusion...
> 
> Some people seem to express a rule as [query->assertion], where the
> antecedent is _explicitly_ a query (i.e. uses different syntax to an
> assertion). Others seem to use [assertion->assertion] where the
> antecedent is only implicitly a query; it is understood in the
> implementation that one checks whether the antecedent assertion is true
> in the fact base. That's all.
> 
> Hence, some people would speak of "matching a query" where others would
> say "matching an assertion" or "matching the antecedent" for exactly the
> same process.

Thanks for the clarification. I propose that we use a term for the
antecedent tthat is NOT "assertion". Furthur, I propose that this term
either be "query" or that the definition express the commonality with
queries.

I feel that vocabulary resolution saves a lot of time in the long run
and is worth some effort. Anybody have proposals for the existing
terms or new terms? For instance, in
Message-Id: <v04210102b7c458a8e31a@[205.160.76.173]> [1] , Pat says:
  It would be better to say that the rules act as a kind of bridge
  between assertions (which match their antecedents) and queries
  (which match their conclusions), rather than that they are
  *composed* of them.
Given recent clarification of my intent, what corrections/wording
would you propose?

[1] http://lists.w3.org/Archives/Public/www-rdf-rules/2001Sep/0036.html

-- 
-eric

(eric@w3.org)
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Received on Friday, 14 September 2001 10:55:11 GMT

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