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Re: [Fwd: Unexpected DISTINCT?]

From: Bijan Parsia <bparsia@cs.man.ac.uk>
Date: Mon, 5 Mar 2007 09:45:53 +0000
Message-Id: <7E1A0BD6-4857-47DE-B9B1-48A98E8FB5FD@cs.man.ac.uk>
Cc: Lee Feigenbaum <feigenbl@us.ibm.com>, RDF Data Access Working Group <public-rdf-dawg@w3.org>
To: andy.seaborne@hp.com

On Mar 5, 2007, at 9:29 AM, Seaborne, Andy wrote:

> The cardinality for extensions of BGP matching isn't prescribed by  
> the spec - it's just a matter of an extension deciding what is  
> appropriate for it's extension.
> http://www.w3.org/2001/sw/DataAccess/rq23/rq25.html#sparqlBGPExtend
> which does not include anything on cardinality induced from blank  
> nodes in BGPs.  Hopefully, that should give freedom to extended  
> matchings such as OWL-DL.

Sorry, I didn't mean to suggest that the spec constrained OWL  
extensions...but if plain SPARQL has an implicit ALL semantics (or an  
implicit "best effort" semantics) it will be more consistent to  
follow that. It seems that even in simpler cases than OWL, ALL might  
not be easiest (for a number of reasons). If number of (extra)  
answers in the non-distinct case *never* mattered, then best effort  
would be fine, but I'm under the impression that people feel strongly  
for stable numbers of answers in the non-distinct case. Having  
explicit ALL with no modifier == best effort seems to accommodate all  
these needs at the cost of departing from the standard SQL behavior.

If stable number of (non-distinct) answers doesn't matter, but only  
an upper bound, then several things become easier spec-wise (though I  
think that is a bit too loose).

Received on Monday, 5 March 2007 09:46:13 UTC

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