[Myexperiment-discuss] MyExperiment SPARQL endpoint returns incorrect results

[Peter Ansell]

Hi,

The SPARQL endpoint at http://rdf.myexperiment.org/sparql isn't
working properly right now for queries with optional unbound items.

The query below should only return bindings for ?linkedRecordType
?label, ?title, or ?skoslabel when they actually exist.

CONSTRUCT {
?s ?p <http://www.myexperiment.org/workflows/72> .
?s a  ?linkedRecordType .
?s  <http://www.w3.org/2000/01/rdf-schema#label> ?label .
?s  <http://purl.org/dc/elements/1.1/title> ?title .
?s  <http://www.w3.org/2004/02/skos/core#prefLabel> ?skoslabel .
} WHERE {
?s ?p <http://www.myexperiment.org/workflows/72> .
OPTIONAL { ?s a ?linkedRecordType . }
OPTIONAL { ?s  <http://www.w3.org/2000/01/rdf-schema#label> ?label . }
OPTIONAL { ?s <http://purl.org/dc/elements/1.1/title> ?title . }
OPTIONAL { ?s <http://www.w3.org/2004/02/skos/core#prefLabel> ?skoslabel . }
} LIMIT 500 OFFSET 0

Right now the Garlik 4Store SPARQL engine is returning bindings that
don't actually exist as blank nodes with an rdf:nodeID="LL". This is
worse than it seems as it is inconsistent. It implies that all of the
resources that will be bound to ?s have labels/titles/prefLabel's, and
that they all point to the same blank node, although there is no other
information available about the blank node they reference.

You may want to try upgrading to the latest version of 4Store as you
are one version behind right now, 1.1.2 is the latest [1].

Cheers,

Peter

[1] http://4store.org/download/