Re: agenda: RDF Data Access 22 Feb

On Mon, Feb 21, 2005 at 12:52:40PM -0600, Pat Hayes wrote:
> >3. SPARQL QL publication
> >
> >ACTION: EricP, make sure editor's draft as an inline issue (to be
> >published) that we need to work this out
> >DONE:
> I notice this in
> used in conjunction with optional, it can be used to test whether a 
> graph pattern with at least one variable in it has been matched. When 
> also used in conjunction with not, it can test to see that a triple 
> has not been asserted. This is called Negation as Failure in logic 
> programming.
> but NOT does not appear in the grammar anywhere. Is this an editing 
> bug, or am I missing something?

fixed. or at least changed...
One may test that a graph pattern is not expressed by specifying an
optional graph patten that introduces a variable and testing to see
that the variable is not bound. This is called Negation as Failure in
logic programming.

This query matches the people with a name but no expressed mbox:

PREFIX foaf: <>
SELECT ?name
 WHERE ( ?x foaf:name  ?name )
       OPTIONAL ( ?x foaf:mbox ?mbox )
   AND !bound(?mbox)

If there were a rule that everyone had an mbox, one would need to:

   AND isBnode(?mbox)

and if there *might* be such a rule:

   AND !bound(?mbox) || isBnode(?mbox)

Should that go into the spec?

All this will make Pat shudder, I'm quite sure.

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Received on Wednesday, 23 February 2005 15:35:06 UTC