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Use of p* in test cases

From: Jan Wielemaker <J.Wielemaker@vu.nl>
Date: Thu, 11 Oct 2012 17:29:57 +0200
Message-ID: <5076E5F5.6080206@vu.nl>
To: <public-rdf-dawg-comments@w3.org>
Hi,

It is not really clear to me whether comments on test cases should be 
sent to this list.  Maybe it is also a comment on the document though.
I'm updating the ClioPatria SPARQL endpoint to 1.1.

One issue that causes me trouble are test cases such as '(pp34) Named 
Graph 1'.  The query is

prefix :  <http://www.example.org/>
select ?t
where {
   GRAPH <ng-01.ttl> {
     ?s :p1* ?t }
}

Given that the * operator matches zero steps and both end-points
are variables, all resources are an answer.  But, what are all
resources?  It seems the test cases assume all resources that
appear as subject or object in the destination graph.  But,
why not all predicates too?   ClioPatria can generate resources,
but it has no clue to what graph these belong :-(

Although I can write an implementation that will answer this
question as the test-cases suggest it should be answered, I
wonder whether it makes much sense to define the behaviour of
this query exactly.  ?x :p* ?y queries can never be answered on
any sensible sized RDF graph anyway.

I'd propose to either use :p1+ for these queries or specify either
the subject or the object.  That avoids these ambiguities.

	Cheers --- Jan

P.s.	Is there a better way to get the test cases than mirroring
	http://www.w3.org/2009/sparql/docs/tests/?  I found a mirror
	git repository on GitHUB, but it was rather outdated when
	I checked.
Received on Thursday, 11 October 2012 15:29:33 GMT

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