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specify the language without reference to implementation; keep inference orthogonal

From: Dan Connolly <connolly@w3.org>
Date: Wed, 22 Dec 2004 09:09:38 -0600
To: RDF Data Access Working Group <public-rdf-dawg@w3.org>
Message-Id: <1103728178.3082.720.camel@dirk>

I think I have mentioned this in IRC now and then, but I don't
think I have sent mail about it. Please specify the language
without reference to implementations.

That is, take out stuff like:

"If a query processor encounters a function that it does not provide,
the query is not executed and an error is returned."
  http://www.w3.org/2001/sw/DataAccess/rq23/#TestingExtensions
  $Revision: 1.160 $ of $Date: 2004/12/17 18:16:17 $


Stuff like "note that the query processor does not have to have any
understanding of the values in the space of the datatype" is perhaps
OK as informal explanation.

"RDF systems are not required to implement the entailements expressed by
these rules, but may choose to do so" looks like it refers to some
standardized notion of "RDF system"; I'm not aware of one. Please
ground it with a link if there is one. And what does "may choose
to do so" mean? Does it impact definitions such as Query Results?
If so, the language isn't well-defined; its definition depends
on implementations.

(hmm... where's the term that's like Query Results but factors
in constraints, optionals, unsaid, and all that?)

I prefer to get rid of the whole section
3.3 Implementation Requirements. If the WG really wants to get
into software conformance clauses, (a) it will have a considerable
impact on our schedule, which is already at risk; I'm not sure
we can do that without extending the duration of the WG,
which requires negotiating with various parties outside the WG,
and (b) the language needs to be specified without reference
to implementations anyway and (c) we'll need clear
definitions for the product classes
(some advice is available in section
2.2 What needs to conform of the QA spec guidelines
http://www.w3.org/TR/2004/WD-qaframe-spec-20041122/#what-conform)


This looks like a pretty clear problem:

"The following are equivalent for a query processor that handles
preciates for mathmatical expressions:"

It seems to me that datatype entailments are no different from
RDFS entailments; some systems pre-compute them and use
the result as the input graph when evaluating queries. That
doesn't change how queries work.

The query written...

WHERE   ( ?x dc:title ?title )
        ( ?x ns:price ?price )
        ( ?price op:numeric-less-than 30 )

will only match if the input graph includes a triple ala

 <#x> op:numeric-less-than 30.

I suggest rewriting "3.4 Constraints and Predicates" to be
include discussion of RDFS, and making it clear that it's
informative, i.e. not part of the definition of the query
language.

I was hoping we could leave the input graph that a service
chooses fairly opaque for v1, but we don't seem to be
able to avoid discussing service descriptions or complex
FROM clauses or something. Hm... I think there's another
issue brewing...


-- 
Dan Connolly, W3C http://www.w3.org/People/Connolly/
D3C2 887B 0F92 6005 C541  0875 0F91 96DE 6E52 C29E
Received on Wednesday, 22 December 2004 15:09:05 GMT

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