Thanks..Its Working!!
for the query
SELECT (NS:MYFunc(3.5) AS ?ThreeSquared) { }
To my observation say suppose I use the MYFunc in a FILTER construct then
it is invoked
several times for each record obtained by the SPO triple pattern specified
in the WHERE clause.
I want to use it in a query like as follows:
SELECT ?Names WHERE {?Name rdf:type NS:SomeClass. FILTER(NS:MYFunc(?Names))}
So in This case for each instance of NS:SomeClass, MYFunc will be invoked.
Another thing that would like to confirm is:
1. What will be the return type of MYFunc
For e.g. If I want to fetch some information regarding to the Instance Name
passed to MYFunc and the Information i want to return is some desciption of
that Instance in say String format.
I am not that much familiar with SPARQL syntax but as mentioned above, i
want MYFunc to return some Information which is returned in the SPARQL
query Result.
On Thu, Dec 19, 2013 at 4:05 PM, Andy Seaborne <[email protected]> wrote:
> On 19/12/13 10:10, Dibyanshu Jaiswal wrote:
>
>> 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?
>>
>
> Yes.
>
> Andy
>
>
>
>>
>> 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
