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Re: A neat, but impractical, solution

From: Pat Hayes <phayes@ihmc.us>
Date: Sun, 6 Aug 2006 21:40:55 -0700
Message-Id: <p06230914c0fc730948cf@[]>
To: Bijan Parsia <bparsia@cs.man.ac.uk>
Cc: RDF Data Access Working Group <public-rdf-dawg@w3.org>

>It occurs to me that one way to manage the 
>distinguished/semidistinguished/nondistinguished mechanism a bit 
>more neatly would be to dispense with the distinction between BNodes 
>and query variables (except for spelling and syntactic restrictions 
>on placements) in queries, and force the range of the variables to 
>depend on the query form. That is, SELECT forces distinguished 
>variables, and ASK the rest.

So there are no bnodes in SELECT patterns, if I follow you (?) That 
seems like a big handicap.

>  We could then allow variables to be listed in the "head" of the ASK 
>clause (as in the SELECT clause), so that the distinction between 
>semi and nondistinguished variables is merely projection/listing in 
>the head.

This sounds very like one of the options we used in DQL, where an ASK 
was basically a SELECT with nothing selected.

>You could list BNodes in the head just like other query variables, 
>or dispense with them altogether, or allow them to have their 
>present form, to wit, being dedicately non-distinguished.

Actually I don't think that is their current role in SPARQL, if I 
understand what you mean by non-distinguished.

>Unfortunately, while rather neat, it's not very practical, as people 
>are used to using SELECT as their query form (a la SQL) and, 
>especially in the RDF case, likely to want semi-distinguished 
>variables by default.

Right. I would strongly oppose restricting variable bindings in RDF 
SPARQL: there is no computational need to do so, and it would make 
the answers incomplete for no good reason.


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Received on Monday, 7 August 2006 04:41:10 UTC

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