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Re: What is an RDF Query?

From: Pat Hayes <phayes@ai.uwf.edu>
Date: Mon, 17 Sep 2001 10:54:13 -0500
Message-Id: <p05101002b7cbc05e16eb@[205.160.76.175]>
To: "Peter F. Patel-Schneider" <pfps@research.bell-labs.com>
Cc: www-rdf-rules@w3.org
>From: "Eric Prud'hommeaux" <eric@w3.org>
>Subject: Re: What is an RDF Query?
>Date: Fri, 14 Sep 2001 10:55:09 -0400
>
>>  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 propose that we do not do this.  I oppose calling the antecedant of a
>rule anything other than the antecedant of a rule!  In particular, I
>strongly oppose calling it a query, as there have been arguments that
>the antecedant of a rule is not the same as a query.

I agree. Also, this proposed terminology embodies a confusion between 
the idea of a syntactic part (of a rule) on the one hand, and a 
propositional attitude (of being asserted or queried) on the other. 
The point is that the *very same* expression can be both asserted and 
queried; being an assertion or a query are not syntactic categories.

We already have a well-established and widely understood terminology 
for talking about rules. Let's stick to it and avoid creating 
confusion where none exists. Rules have antecedents and consequents, 
and are often (though not always) understood to have the logical 
force of implications, ie when asserted, they say that the 
antecedents entail the (disjunction of the) consequent(s). (In 
another sense of 'rule' they have no particular logical force, but 
are simply thought of as process specifications, like productions in 
a production system. Often, people switch back and forth between the 
'logical' and 'processing' ways of thinking, but the 
antecedent/consequent terminology works in both cases.)

The term 'query' has several meanings as well. If we are thinking 
logically, then an expression is a query just by virtue of being 
posed as a goal to be proved; its not a syntactic matter so much as a 
matter of pragmatics, so of course there is a "commonality" between 
queries and consequents (not antecedents), i.e. they are the same 
kinds of expressions; they can be unified by variable matching. 
(Though even there one has to keep the assertion/querying distinction 
clear since the same variables are treated differently in the two 
cases.) But 'query' is also used in a broader sense to mean something 
more complicated, a kind of description or specification of the data 
that is being requested, and may require more complicated kinds of 
processing than simply checking logical consequence. In this case it 
isn't so clear that there is any straightforward commonality between 
the query language and any part of the rule syntax.

>  > I feel that vocabulary resolution saves a lot of time in the long run
>>  and is worth some effort.
>
>I feel that the vocabulary conflation can only serve to stifle debate on
>exactly what rule antecedants should be.

I agree with both of you.

Pat

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Received on Monday, 17 September 2001 11:54:09 GMT

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