It seems to me that this is a case of the standard being clear and there being
a compelling use case which is better addressed by other behavior.
It is certainly possible to build an application that *uses* the standard
behavior to do logic with the graph names, and hence the standard is not
demonstrably wrong, simply arguably less useful than it might have been
e.g. I believe one way of doing an intersection between sets of names of graphs
in your triple store is with nested subselects using from named.
select ?g
FROM NAMED <g1>
FROM NAMED <g3>
{
{ SELECT ?g
FROM NAMED <g2>
FROM NAMED <g3>
{ GRAPH ?g {} }
}
}
should return <g3> whereas with (the obvious extension of) your proposal it
should give an error with <g2>
Jeremy J Carroll
Principal Architect
Syapse, Inc.
On Nov 15, 2013, at 8:27 AM, Thomas Visel <[email protected]> wrote:
> Andy,
>
> Section 13.3.2 of the SPARQL spec deals with Restricting by Graph IRI. There
> is a question of intended behavior when the specified IRI is neither among
> the FROM NAMED statements nor supplied by the Http protocol.
>
> One could presume from the example and text of Section 13.3.2 that nothing
> gets returned, to put it simply. Another option is that rather than
> returning an empty set, the handler errors of because of an improperly framed
> query. The answer has implications for query optimization.
>
> The issue is more clearly seen in the example (following) from Section
> 13.3.3, wherein the results of a GRAPH restricted by <IRI> are used as the
> basis for a subsequent GRAPH restricted by a variable.
>
> PREFIX data: <http://example.org/foaf/>
> PREFIX foaf: <http://xmlns.com/foaf/0.1/>
> PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#>
>
> SELECT ?mbox ?nick ?ppd
> FROM NAMED <http://example.org/foaf/aliceFoaf>
> FROM NAMED <http://example.org/foaf/bobFoaf>
> WHERE
> {
> GRAPH data:aliceFoaf_baddie
> {
> ?alice foaf:mbox <mailto:[email protected]> ;
> foaf:knows ?whom .
> ?whom foaf:mbox ?mbox ;
> rdfs:seeAlso ?ppd .
> ?ppd a foaf:PersonalProfileDocument .
> } .
> GRAPH ?ppd
> {
> ?w foaf:mbox ?mbox ;
> foaf:nick ?nick
> }
> }
>
> Reframed, the question is this: When the <IRI> is correctly formed yet not
> included in a FROM NAMED (or Http protocol), ought the behavior be to error
> off from an improper query or simply return the empty set? (Obviously, under
> some engine implementations it makes no difference.)
>
> Regards,
>
> Thomas Visel
>
>
> <image001.png>
> Thomas A. Visel, Senior Translation Engineer
> Office: 512-651-5834
> Email: tviselalgebraixdata.com
> www.algebraixdata.com
>
