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Re: unsaid/not: any champions?

From: Steve Harris <S.W.Harris@ecs.soton.ac.uk>
Date: Mon, 4 Oct 2004 17:14:19 +0100
To: RDF Data Access Working Group <public-rdf-dawg@w3.org>
Message-ID: <20041004161419.GM19546@login.ecs.soton.ac.uk>

On Mon, Oct 04, 2004 at 04:09:14PM +0100, Andy Seaborne wrote:
> I also think it will have significant impact on the design and wouldn't
> want this feature to defocus our efforts.  It seems to force either a
> logical assertion view of the world or a procedural interpretation.  We
> have some implementation experience to go on (log:notIncludes in cwm and
> Euler) but are there any database-backed systems that provide something of
> this kind?
> 
> Simon/Tom - does Kowari prvide any similar feature?  I have had requests
> for it in the past but it is not a common request (I guess I have had less
> than 5 such requests).
> 
> As it is an objective - "4.3 Non-existent Triples" - we have some room for
> manoeuvre.
> 
> http://www.w3.org/2001/sw/DataAccess/UseCases#d4.3
> 
> 
> I would note that limited cases can be with extension functions,
> particularly testing for the absence of a single triple after variables
> have been bound.  Optionals can be used as the basis for post-query
> checking by the application in some cases.  The ASK form is also relevant.

It does not neccesarily have to be application level:

SELECT ?x
WHERE (?x rdf:type foaf:Person)
      (?x foaf:mbox_sha1sum ?sum UNSAID)   # playing with dave's syntax

SELECT ?x
WHERE   (?x rdf:type foaf:Person)
      [ (?x foaf:mbox_sha1sum ?sum) ]
AND &dawg:unbound(?sum)

( "AND ?sum IS NULL" if we go down the three value logic route )
obviously the 2nd example is not as easy to read.
 
> For this publishing cycle, I am inclined to leave a placeholder in the doc
> and possibly explicitly note that this feature may fall below the cut
> line.  The sort of feedback I'd like to see is real use cases to gauge the
> overall value.   If there is no feedback, then we drop it.

I've seen a similar level of requests to Andy (3 or so IIRC), and they
tended to be very special purpose, data maintainance type questions,
rather than data-accessy things.

- Steve
Received on Monday, 4 October 2004 16:14:25 GMT

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