On 3/19/2013 9:39, [email protected] wrote:
Hey Holger,
thanks for the explanation. I'm using SPIN API in the implementation
of Graphity Linked Data platform which has the following processing model:
- request URI is matched against resource templates (classes) in a
sitemap ontology like this one:
https://raw.github.com/Graphity/graphity-ldp/rf-input-mode/src/main/resources/org/graphity/platform/ontology/sitemap.ttl
- each of the template classes has a DESCRIBE/CONSTRUCT spin:Template
attached to it via spin:constraint. Common SPIN Templates are grouped
in a separate ontology:
https://raw.github.com/Graphity/graphity-ldp/rf-input-mode/src/main/resources/org/graphity/platform/vocabulary/gp.ttl
Each of the templates also indicate the source RDF dataset of the
resource, which normally has a SPARQL endpoint.
- SPARQL query string is generated from the TemplateCall, the request
URI is bound to ?this variable afterwards, and the query is executed
on the endpoint of the dataset of the resource
- the result RDF is returned as the response (if the resource matched
no template or the query result is empty, 404 is returned)
Having an RDFNode of the spin:constraint object, I'm converting it to
TemplateCall using SPINFactory.asTemplateCall() and run
getQueryString() to generate the SPARQL query string. Around line #400
here:
https://github.com/Graphity/graphity-ldp/blob/rf-input-mode/src/main/java/org/graphity/platform/model/ResourceBase.java
Afterwards I'm binding ?this variable to a URI value using simple
string replacement.
If there is a better alternative to generate SPARQL query strings from
TemplateCall (and maybe bind variable(s) to URIs at the same time), I
will be happy to refactor my code.
I have spent some time refactoring yesterday to get rid of most usages
of TemplateCall.getQueryString() and I believe I will deprecate or
delete it altogether. The alternative in your case is to create a
QueryExecution instead of a Query. In that QueryExecution you would use
qexec.setInitialBindings() to tell it about the argument values of the
template call (and also ?this in your case - the text replacement in the
query string looks fragile). I have added a convenience method to
TemplateCallImpl:
@Override
public QuerySolution getInitialBinding() {
QuerySolutionMap map = new QuerySolutionMap();
Map<String,RDFNode> input = getArgumentsMapByVarNames();
for(String varName : input.keySet()) {
RDFNode value = input.get(varName);
map.add(varName, value);
}
return map;
}
This produces the QuerySolutionMap which you can pass to
qexec.setInitialBindings(). You then just need the "static" query string
from the template's body - which is the same for all instances of the
template calls. In order to get the ARQ Query object itself, something
like the following should work
ARQFactory.get().createQuery((org.topbraid.spin.model.Query)template.getBody());
HTH
Holger
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