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Re: Question on variable scope w.r.t. multiple optional blocks

From: Yoshio FUKUSHIGE <fuku@w3.org>
Date: Tue, 14 Dec 2004 20:41:27 +0900
Message-ID: <004001c4e1d1$d8de7a90$f1e41b85@steelball>
To: "Steve Harris" <S.W.Harris@ecs.soton.ac.uk>, <public-rdf-dawg@w3.org>

>> PREFIX foaf: <http://xmlns.com/foaf/0.1/>
>> SELECT ?name, ?nick
>> WHERE (?x foaf:name ?name)
>>          [(?x foaf:nick ?nick)
>>           (?x foaf:givenname ?nick)]
>>          [(?x foaf:nick ?nick)
>>           (?x  foaf:surname ?nick)]
> This would be quite confusing as you could get one solution with two
> different results for ?nick, using the current execution model. I think.

Thank you, Steve,  for pointing it out.
Yes, you are right.

The optional conditions can be met at the same time, which slipped
from my mind...

Hmm, what can I do with my uneasiness...

It comes from the fact that whenever one adds a new clause to a query
under construction, one has to check if variables in the new clause 
with other variables in existing clauses.

Do you think it is a painful but unevitable and necessary task for users?
Or at least a realistic solution?

Only if we had some mechanism for explicitly denoting the scope of the 
Introducing such mechanism, however, would be very laborious...


Received on Tuesday, 14 December 2004 11:41:31 UTC

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