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Re: 3.6 Optional Match

From: Steve Harris <S.W.Harris@ecs.soton.ac.uk>
Date: Wed, 4 Aug 2004 19:18:32 +0100
To: public-rdf-dawg@w3.org
Message-ID: <20040804181832.GB16329@login.ecs.soton.ac.uk>

On Wed, Aug 04, 2004 at 09:54:10 -0700, Bob MacGregor wrote:
> BRQL should be commended in adding the OPTIONAL
> clause.  However, I see two problems.  First is that it doesn't
> support nested optional matches (their document acknowledges
> this issue).  Second, BRQL makes a distinction between
> WHERE and AND restrictions.  Both of these should be
> allowable in the OPTIONAL clause, but they aren't (as far
> as I can tell). 

I disagree with this for a number of reasons, first, I think AND is
helpful for readability and familarity to SQL users, and I dont think that
optional AND makes sense in many examples, eg:

a)	SELECT ?x
	WHERE (<foo>, <bar>, ?x)
	OPTIONAL (?x, <math:greater-than>, 120.0)

is equivalent to

b)	SELECT ?x
	WHERE (<foo>, <bar>, ?x)

as far as I can see.

c)	SELECT ?x, ?y
	WHERE (<foo>, <bar>, ?x)
	OPTIONAL (?x, <math:greater-than>, ?y)

is different to b), but I'm not sure what it would be useful for in
real-world examples, and it would infact be quite dangerous to allow
queries of this sort.

- Steve
Received on Wednesday, 4 August 2004 14:18:38 UTC

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