Fwd: SPARQL Bindings Example on W3C WD

Pre LC comment:

-------- Original Message --------
Subject: 	SPARQL Bindings Example on W3C WD
Date: 	Thu, 14 Jul 2011 20:13:44 +0700
From: 	Fariz Darari

	

	

...

I am interested in SPARQL and am using it in my Semantic Web project, 
especially the Federated Query feature. I have read the SPARQL Federated 
Query extension specification 
(http://www.w3.org/2009/sparql/docs/fed/service). I have been wondering 
of the BINDINGS operative query example:

PREFIX : <http://example.org/>
PREFIX foaf: <http://xmlns.com/foaf/0.1/>
SELECT ?s ?o1 ?o2
{
   ?s ?p1 ?o1
   OPTIONAL { SERVICE <http://example.org/sparql> {?s foaf:knows ?o2 }}
} BINDINGS ?o2 {
  (:b)
}

Shouldn't it give the resulting sequence like below?

so1o2
<http://example.org/a>"alan@example.org 
<mailto:alan@example.org>"<http://example.org/b>
<http://example.org/a>"Alan"<http://example.org/b>
<http://example.org/a>"bob@example.org 
<mailto:bob@example.org>"<http://example.org/b>
<http://example.org/a>"Bob"<http://example.org/b>
<http://example.org/c>"alice@example.org 
<mailto:alice@example.org>"<http://example.org/b>
<http://example.org/c>"Alice"<http://example.org/b>

I think that it's the OPTIONAL keyword that makes the result like that.
...

Best regards,
Fariz Darari