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RE: What is an RDF Query?

From: Pat Hayes <phayes@ai.uwf.edu>
Date: Wed, 19 Sep 2001 10:26:30 -0500
Message-Id: <p05101010b7ce661cc6e1@[]>
To: "Wagner, G.R." <G.R.Wagner@tm.tue.nl> (by way of "Ralph R. Swick" <swick@w3.org>)
Cc: w3c-rdfcore-wg@w3.org
>[freed from spam trap -rrs]
>Date: Sun, 16 Sep 2001 17:28:51 -0400 (EDT)
>Message-ID: <511BB18E82E9D11188230008C724064602D9DDAC@tmex1.tm.tue.nl>
>From: "Wagner, G.R." <G.R.Wagner@tm.tue.nl>
>To: "'Peter F. Patel-Schneider '" <pfps@research.bell-labs.com>,
>         "'eric@w3.org '" <eric@w3.org>
>Cc: "'www-rdf-rules@w3.org '" <www-rdf-rules@w3.org>
>>>  Thanks for the clarification. I propose that we use a term for the
>>>  antecedent that 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! 
>It's not a matter of how you call it, but what form it may
>have, or, in other words, from which language it comes.
>Obviously, any practical KR system, such as Prolog, relational
>databases, or RDF, has an assertion (or input) language defining
>the admissible (logical) expressions that may be asserted/inserted
>into a KB, and it has a query language defining the admissible
>expressions for querying/retrieving knowledge.

Sorry, but I don't find  that at all obvious, particularly if it is 
supposed to imply that these must be different languages.  And it IS 
a matter of how you call it; we are having a debate here about proper 
terminology. Such discussions do matter, since enormous amounts of 
time can be wasted in an interdisciplinary discussion by inadvertant 
clashes of terminology. For example:

>Both with respect to bottom-up and to top-down evaluation

These terms 'bottom-up' and 'top-down' are meaningless to me, I'm 
afraid. Apparently they are based on some kind of vertical analogy, 
but I don't know which way up the paper is supposed to be; I tend to 
think from left to right, forwards and backwards.

>it is
>natural then to define a derivation rule for a specific KR system
>in such a way that its antecedant is a query expression and its
>consequent is an input expression.

I have no idea what 'query expression' and 'input expression' mean 
here. In my terminology, a query expression would be one which was 
used for querying, so it presumably couldn't possibly be *part* of a 
rule (though it might match a part of a rule).
My basic point is that the functional roles of expressions and parts 
of expressions in an inference or rule-manipulating system should not 
be identified with their syntactic or logical descriptions, since the 
same structure, with the same logical meaning, can often be used for 
different functional purposes in different contexts. More generally, 
it is mistake to identify logical or assertional meaning with any 
particular kind of processing; the basic utility of logical analyses 
of meaning is that they allow different computational strategies to 
co-exist. So I want us not to adopt terminology which makes such 
identifications pre-emptively.

Pat Hayes
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Received on Wednesday, 19 September 2001 11:26:35 UTC

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