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Re: GRAPH details and test cases

From: Lee Feigenbaum <feigenbl@us.ibm.com>
Date: Mon, 26 Jun 2006 09:35:13 -0400
To: andy.seaborne@hp.com
Cc: dawg mailing list <public-rdf-dawg@w3.org>
Message-ID: <OF1CAB04CF.2DD6E241-ON85257199.004A7BE6-85257199.004AA134@us.ibm.com>

"Seaborne, Andy" <andy.seaborne@hp.com> wrote on 06/26/2006 05:13:26 AM:

> > 1/ Nested GRAPH statements
> > 
> > I didn't find any examples or tests that involved nested GRAPH 
statements, 
> > but the spec made it pretty clear what should happen and SPARQLer 
agrees.
> > 
> > ng1.n3:
> > 
> > :s :p :o, :o1 .
> > 
> > ng2:n3:
> > 
> > :s :p :o, :o2 .
> > 
> > query:
> > 
> > SELECT ?o 
> > FROM NAMED <ng1.n3>
> > FROM NAMED <ng2.n3>
> > {
> >   GRAPH <ng1.n3> {
> >     GRAPH <ng2.n3> {
> >       :s :p ?o .
> >     }
> >   }
> > }
> > 
> > results:
> > 
> > ?o/:o
> > ?o/:o2
> > 
> > why? GRAPH takes the given named graph and places it as the default 
graph 
> > in the RDF dataset against which the inner graph pattern is matched. 
So, 
> > nested graphs basically act as a stack of default-graph contexts for 
the 
> > graph patterns that they contain.
> 
> What were you expecting?  GRAPH <ng2.n3> makes ng2:n3 the target 
> graph for the 
> pattern { :s :p ?o }, which gives the results shown.  In stack terms, it 
is a 
> stack of names, the active one being the stack front.  There's not 
merging of 
> graphs

The results that I got were exactly what I was expecting. I was only 
including that case as a potential test case as it's potentially a 
non-obvious situation which would be good to include in the test suite.

> > 2/ using blank nodes for graph parameter
> > 
> Fred has suggested a syntax change that would remove blank nodes from 
the 
> graph name slot of GRAPH.  I agree that this would be a good change.
> 
> [25] GraphGraphPattern ::= 'GRAPH' VarOrBlankNodeOrIRIref 
GroupGraphPattern
> 
> becomes
> 
> [25] GraphGraphPattern ::= 'GRAPH' VarOrIRIref GroupGraphPattern
> 
> and
> [43] VarOrBlankNodeOrIRIref ::=  Var | BlankNode | IRIref
> 
> can be dropped.

I would be happy with this change.

Lee
Received on Monday, 26 June 2006 13:35:41 GMT

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