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openRDF.org Forum » Sesame & Rio: Help » Thread: SPARQL - Filter Namespaces

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Aug 31, 2008 10:38:19 AM

turnguard
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Joined: Mar 22, 2008
Posts: 34
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SPARQL - Filter Namespaces

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hy there!

1. is there a native sparql [ maybe serql ] way of filtering query out according to a namespace :
for example if you have owl and skos is your store and want to only show classes with the
skos-namespace [ i can't use contexts to make them look different ] .

2. if not : is there a way i could teach the sparql - engine the arq-extension functions from here
http://jena.sourceforge.net/ARQ/library-function.html

any help appreciated
wkr www.turnguard.com

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Aug 31, 2008 7:37:15 PM

turnguard
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Re: SPARQL - Filter Namespaces

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i allready found out myself , very simple ...

public class NameSpace implements Function {

public String getURI() {
return "http://www.turnguard.com/functions#namespace";
}

public Value evaluate(ValueFactory valueFactory, Value... args) throws ValueExprEvaluationException {
try {
URI u = (URI)args[0];
return valueFactory.createURI(u.getNamespace());
} catch (Exception e){
throw new ValueExprEvaluationException();
}
}
}

might not be elegant, but it exactly does what i need

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Aug 31, 2008 7:44:31 PM

turnguard
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Re: SPARQL - Filter Namespaces

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so i can use the above class like this

PREFIX rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#>
PREFIX skos: <http://www.w3.org/2004/02/skos/core#>
PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#>
PREFIX owl: <http://www.w3.org/2002/07/owl#>
PREFIX tg:<http://www.turnguard.com/functions#>

SELECT DISTINCT ?Class
WHERE {
{
?Class rdf:type <http://www.w3.org/2000/01/rdf-schema#Class> .
OPTIONAL {
?Class rdfs:subClassOf <http://www.w3.org/2000/01/rdf-schema#Class> .
}
} . FILTER(tg:namespace(?Class)=<http://www.w3.org/2004/02/skos/core#>)
}

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Sep 1, 2008 8:22:00 AM

arjohn
OpenRDF project lead

The Netherlands
Joined: Jan 23, 2004
Posts: 1289
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Re: SPARQL - Filter Namespaces

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Good that you've found this yourself. Info for any future readers: one can implement the org.openrdf.query.algebra.evaluation.function.Function interface to implement your own functions. After registering the function implementation in the appropriate service description file (/META-INF/services/org.openrdf.query.algebra.evaluation.function.Function) it will be available to Sesame's query engine.

Note that SeRQL natively supports the NAMESPACE function, e.g.:

SELECT DISTINCT Class
FROM {Class} rdf:type {rdfs:Class};
            [rdfs:subClassOf {rdfs:Class}]
WHERE
   NAMESPACE(Class) = skos:
}
USING NAMESPACE
skos = <http://www.w3.org/2004/02/skos/core#>

----------------------------------------
Arjohn Kampman, OpenRDF project lead, Aduna

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Sep 1, 2008 8:47:34 AM

turnguard
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Joined: Mar 22, 2008
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Re: SPARQL - Filter Namespaces

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or register the new function like so

org.openrdf.query.algebra.evaluation.function.FunctionRegistry.getInstance().add(new Namespace());

if you're experiencing any troubles with META-INF and tomcat or so..

Namespace implements Function in this case . see above

wkr turnguard

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