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Re: Disjunction vs. Optional ... and UNION

From: Bob MacGregor <bmacgregor@siderean.com>
Date: Tue, 22 Mar 2005 09:29:20 -0800
Message-ID: <424055F0.9010109@siderean.com>
To: andy.seaborne@hp.com
CC: Dan Connolly <connolly@w3.org>, public-rdf-dawg-comments@w3.org


>> <clip>.  First, I am assuming that the
>> following query returns no bindings:
>> SELECT ?x ?y
>>   WHERE  { ?book dc10:title ?x }
>> I shouldn't since it doesn't refer to OPTIONAL or UNION within the 
>> query, and the
>> spec cites those as prerequisites for allowing unbound values.
> Could you please say where in the spec you found text to draw that 
> conclusion? It is not true.
> It says in 2.1
> """
> Optional matches and alternative matches may leave some variables 
> unbound (see the bound test).
> """
> which is true about solutions to patterns; the text is not about 
> SELECT results.

The impression that I am getting is that the committee is unaware how 
unorthodox the semantics
is for SPARQL.  I was using Occam's razor, assuming that if the language 
is designed to leave variables unbound,
then it would say that up front.  The language you cite above is the 
only language that speaks directly to this issue.
The document contains no examples like the one up above.

> The query
> SELECT ?x ?y
>   WHERE  { ?book dc10:title ?x }
> can return bindings - it's a projection of a query solutions involving 
> ?x and ?book.
This is a horrendous decision by the committee.  The above query ought 
to be flagged as illegal.
Given that RDF is basically a small subset of FOL, its not at all clear 
to me why you are
inventing a brand new semantics that does not resemble any of the 
mainstream logic languages.

Regards, Bob
Received on Tuesday, 22 March 2005 17:29:58 UTC

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