- From: Steve Harris <S.W.Harris@ecs.soton.ac.uk>
- Date: Wed, 22 Dec 2004 14:49:36 +0000
- To: RDF Data Access Working Group <public-rdf-dawg@w3.org>
On Wed, Dec 22, 2004 at 08:43:48AM -0600, Dan Connolly wrote:
> > PREFIX : <http://example.org/ns#>
> >
> > SELECT ?person
> > WHERE (?person :email ?e1)
> > OPTIONAL { (?person :email ?e2) AND ?e2 NE ?e1 }
> > AND ! &dawg:bound(?e2)
> >
> > using the same method Steve had of using optional, then inverting the sense
> > of the match with dawg:bound.
>
> I thought dawg:bound was sort of wishful thinking in an earlier
> message... I had trouble finding it in the editor's draft...
> do you mean isBound in 11.2.2?
> http://www.w3.org/2001/sw/DataAccess/rq23/#sparqlTests
It was wishful thinking when I was using it. I should have checked the
draft though.
> "Return true if its argument, which may be an expression, is defined.
> NaNs and INFs count as defined."
>
> Surely the arguments to operators are the *values* of expressions,
> right?
>
> for example
>
> "fn:compare Compare two strings.. Returns -1, 0, or 1, according to the
> rules of the collation used."
>
> If I write
> fn:compare(?x, "abc")
>
> it's not comparing the 3-character string "?x" with the
> 5-character string '"abc"'; rather, it's comparing whatever
> ?x is bound to with the 3-character string "abc", right?
>
> So the specification of isBound has use/mention bugs... operators
> can't see variable names. isBound would have to be a language
> keyword, like UNSAID or SOURCE.
Yes, but SQL for eg. has tri-value logic (true, false and NULL), so you
can meaningfully apply operators and functions to unbound values (NULL).
I have said a few times that DAWG I think should come down off the fence
about tri-value logic.
- Steve
Received on Wednesday, 22 December 2004 14:49:48 UTC