Hi Martynas,
this is indeed not working correctly (in the current SPIN API release
1.3.0). The role of this method is to return a parsable query string
with the given variables of the template call pre-bound. The problem is
that the current code is expecting to apply variable substitutions while
printing the query string from the RDF tree. However, if no RDF tree
exists, it simply returns the sp:text unchanged.
I believe I can provide a partial fix, but thinking more about this
method I am wondering whether it should be deprecated altogether or at
least have some severe warnings around it. Background: SPIN constraints
and inferencing algorithms do not use this mechanism (of hard-wiring the
variables in the query string) because it is comparably slow (to create
the new strings each time - they are hard to cache) and because there
are cases where the approach doesn't work in general. Consider you have
a bound(?x) statement in the WHERE clause, but then ?x is pre-bound: it
would create a non-parsable string. The approach that SPIN API uses in
most other places is to keep the query strings (or Query objects) and
the initial bindings in separate structures, and then let the Jena
engine do the substitution at run-time - not only the query String but
on the Query and algebra objects.
So before we can make a decision on the future of this
TemplateCall.getQueryString method: could you clarify what your use case
is and whether you could also soft-bind the substitutions? If you could
refactor your surrounding code then I could probably just deprecate this
method for good.
Thanks
Holger
On 3/17/2013 5:56, [email protected] wrote:
Hey Holger,
I have a spin:Template with an argument (in gp: namespace):
:DescribeInstancesTemplate a spin:Template ;
spin:constraint [ a spl:Argument ;
spl:predicate :type ;
spl:valueType rdfs:Resource
] ;
spin:body [ a sp:Describe, sp:Query ;
sp:resultNodes (_:instanceVar) ;
sp:text """DESCRIBE ?instance WHERE {
{
SELECT ?instance
WHERE {
?instance a ?type .
}
} .
}"""^^xsd:string ;
sp:where ([ a sp:SubQuery ;
# full RDF representation follows here
_:instanceVar sp:varName "instance"^^xsd:string .
When called it like this
spin:constraint [ a gp:DescribeInstancesTemplate ;
gp:type owl:Ontology
] ;
I get the query I want (using the TemplateCall.getQueryString() method):
DESCRIBE ?instance
WHERE
{ { SELECT ?instance
WHERE
{ ?instance <http://www.w3.org/1999/02/22-rdf-syntax-ns#type>
<http://www.w3.org/2002/07/owl#Ontology> }
}
}
However, if I change the template's query to use spin:text only:
:DescribeInstancesTemplate a spin:Template ;
spin:constraint [ a spl:Argument ;
spl:predicate :type ;
spl:valueType rdfs:Resource
] ;
spin:body [ a sp:Describe, sp:Query ;
sp:text """DESCRIBE ?instance WHERE {
{
SELECT ?instance
WHERE {
?instance a ?type .
}
} .
}"""^^xsd:string ] .
the ?type argument is not set:
DESCRIBE ?instance
WHERE
{ { SELECT ?instance
WHERE
{ ?instance <http://www.w3.org/1999/02/22-rdf-syntax-ns#type>
?type }
}
}
Is that the expected behaviour or am I missing something? spin:text
syntax is a really nice simplification, but I would expect Template
and TemplateCall to work the same way.
Martynas
graphity.org
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