>From the reply what I can figure out is: I need to perform 2 steps.
1. To register the function class with a given URI using -
FunctionRegistry.get().put(String uri, Class<?> funcClass)
2. To make a new Class for that function which extends FunctionBase1 or say
implements class Function. Where I need to write my function definition in
MyFunction.exec(NodeValue v){}
After which I can use my defined function like any other inbuilt ARQ
function.
Am I right?
On Thu, Dec 19, 2013 at 3:07 PM, Andy Seaborne <[email protected]> wrote:
> On 19/12/13 05:30, Dibyanshu Jaiswal wrote:
>
>> Hi all!
>>
>> I want to define my own functions which i would like to use via a SPARQL
>> query. For E.g.
>>
>> SELECT (<http://example/square>(3) AS ?ThreeSquared) { }
>>
>> 1. SELECT (<myFunctionURI>(parameter) AS ?x){}
>> OR
>> 2. SELECT ?names WHERE { ?names rdf:type NS:ClassA.
>> FILTER(NS:myFunction(?names)}
>>
>> Is that possible??
>>
>> The corresponding effort made by me is as follows:
>> The following package :
>> com.hp.hpl.jena.sparql.function.user<http://jena.
>> apache.org/documentation/javadoc/arq/com/hp/hpl/jena/
>> sparql/function/user/package-summary.html>and
>> its class
>> UserDefinedFunctionFactory<http://jena.apache.org/
>> documentation/javadoc/arq/com/hp/hpl/jena/sparql/function/user/
>> UserDefinedFunctionFactory.html>gives
>>
>> a brief description of defining our own functions which supports as
>> shown in Example 1 above. But I need something like Example 2 shown above.
>> Having browsing Jena-core and ARQ Javadocs, I can find classes like
>> FunctionFactory, FunctionRegistry, FunctionBase etc, by which I see some
>> hope of what I want. Can I achieve this? Or such function are limited to
>> the ARQ engine and cannot be expanded?
>>
>> To Breif: I want to define a fuction, register it with a URI and hence use
>> it via SPARQL Query Engine as NS:myFunction() in FILTER and etc constructs
>> of a SPARQL query.
>>
>>
>>
> Yes - you can do that. ARQ, internally, uses the public mechanism to add
> all the additional functions that are not keywords in the langauge.
>
> UserDefinedFunctions are, in fact, macros for expressions.
>
> Completely new functionality is added by implemenign
>
> Take FN_Abs (which is fn:abs or <http://www.w3.org/2005/xpath-
> functions#abs -- the form of the URI does not matter as the compiler
> expands them all during parsing.
>
> The same functions act in filters and SELECT expressions. Your examples 1
> and 2 are using the same mechanism.
>
> See
> com.hp.hpl.jena.sparql.function.StandardFunctions
>
> The core function is:
>
> FunctionRegistry.get().put(String uri, Class<?> funcClass)
>
> or specifically
>
> registry.put(
> "http://www.w3.org/2005/xpath-functions#abs";,
> FN_Abs.class)
>
>
> and the implementation is
>
> public class FN_Abs extends FunctionBase1
> {
> public FN_Abs() { super() ; }
>
> @Override
> public NodeValue exec(NodeValue v)
> { return XSDFuncOp.abs(v) ; }
> }
>
> Your code must implement interface Function.
>
> There are helper classes for the cases of one, two, three and four
> arguments. Functions, in general, can be variable numbers of arguments.
>
> FunctionRegistries can be per query execution - I've shown using the
> global one which is usually all you need.
>
> Andy
>
>
>
>
>
--
*Dibyanshu Jaiswal*
Mb: +91 9038304989
Mb: +91 9674272265
