Hi,
I've run into a problem involving a SPARQL query that takes parameters
as a VALUES block (from the skos-history project [1]). The query works
differently in Jena 3.0.1+ than it used to. I believe this may be
related to variable scoping fixes made as part of JENA-1018.
The original query is quite complicated but I've made a minimal example
which demonstrates the same issue.
Use this data loaded into the graph <data.ttl>:
@prefix ex: <http://example.org/>.
ex:itemA a ex:TypeA .
ex:itemB a ex:TypeB .
And this query:
PREFIX ex: <http://example.org/>
SELECT * {
VALUES (?graph ?type) { (<data.ttl> ex:TypeB) }
GRAPH ?graph {
BIND(ex:TypeA AS ?defaulttype)
BIND(COALESCE(?type, ?defaulttype) AS ?realtype)
?item a ?realtype .
}
}
The idea of the VALUES block is to specify parameters for the remaining
query. In particular, the ?type parameter can be set to an explicit
value (here ex:TypeB) or left undefined (using undef). If it is left
undefined, then the default type (ex:TypeA) will be used instead.
Here is the result using Jena 3.0.0:
$ ~/sw/apache-jena-3.0.0/bin/sparql --namedGraph data.ttl --query test.rq
-------------------------------------------------------------
| graph | type | defaulttype | realtype | item |
=============================================================
| <data.ttl> | ex:TypeB | ex:TypeA | ex:TypeB | ex:itemB |
-------------------------------------------------------------
But with Jena 3.0.1 (also current 3.1.0-SNAPSHOT):
$ ~/sw/apache-jena-3.0.1/bin/sparql --namedGraph data.ttl --query test.rq
-------------------------------------------------------------
| graph | type | defaulttype | realtype | item |
=============================================================
| <data.ttl> | ex:TypeB | ex:TypeA | ex:TypeA | ex:itemA |
-------------------------------------------------------------
So with 3.0.0 the query worked as intended, ex:TypeB was used to query
the data. But with 3.0.1 the default type (ex:TypeA) will always be used.
If I move the VALUES clause inside the GRAPH block then also Jena 3.0.1
will give the expected result, i.e. use ex:TypeB as ?realtype and return
ex:itemB as ?item.
Am I right that the original query relies on unspecified/wrong behavior
(the variables defined in VALUES outside the GRAPH block should not be
in scope inside the GRAPH block) and that the right solution is to move
the VALUES block inside GRAPH? I want to double-check before making
changes to a large number of queries that rely on this.
Thanks,
Osma
[1] https://github.com/jneubert/skos-history
--
Osma Suominen
D.Sc. (Tech), Information Systems Specialist
National Library of Finland
P.O. Box 26 (Kaikukatu 4)
00014 HELSINGIN YLIOPISTO
Tel. +358 50 3199529
osma.suomi...@helsinki.fi
http://www.nationallibrary.fi
