Hi all,
I am not an expert of the semantics of how OPTIONAL works in SPARQL but I am a
little surprised at some results I am getting. I am executing the following
queries on a copy of the database which is normally at
http://go.bio2rdf.org/sparql although it is down at the moment.
No results query:
SELECT * WHERE { GRAPH <http://bio2rdf.org/go> { OPTIONAL {
<http://go.bio2rdf.org/go:0032283> <http://www.w3.org/2000/01/rdf-schema#label>
?label . } OPTIONAL { <http://go.bio2rdf.org/go:0032283>
<http://purl.org/dc/elements/1.1/title> ?title . } OPTIONAL {
<http://go.bio2rdf.org/go:0032283> <http://owl.bio2rdf.org/go#name> ?goName }
} }
Results query:
SELECT * WHERE { GRAPH <http://bio2rdf.org/go> { OPTIONAL {
<http://go.bio2rdf.org/go:0032283> <http://owl.bio2rdf.org/go#name> ?goName }
} }
The only difference between the queries is that I take out two of the optional
statements and it returns the result which should have matched in the first
one... Or am I doing something wrong?
For reference, I am trying to efficiently seek a label for a given item without
knowing beforehand which predicate will be there, as the subject URI is
generated from a query on the bio2rdf software which in turn generates the
SPARQL query (I am actually using a CONSTRUCT internally but the behaviour is
the same as the SELECT)
Cheers,
Peter
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