Hi Andy
Thanks for answering! I'll look into OpExecutor to see if I get somewhere.
Couldn't find the webpage to this quack library, is it published yet?
Cheers,
Dfcp
On Tuesday, September 3, 2013 <x-apple-data-detectors://24>, Andy Seaborne
wrote:
> On 02/09/13 19:03, Diogo FC Patrao wrote:
> Hi
>>
>> I'm running a query with join results from two endpoints:
>>
>> SELECT * {
>> SERVICE <s1> { ?a a :Class1 } # q1
>> SERVICE <s2> { ?a a :Class2 } # q2
>> }
>>
>> I noticed (by running ARQ 2.8.8 with -v) that it first dispatches query q1
>> on s1 and then one query q2 on s2 *for each result* in the previous query.
>>
>> Is there any other way of doing it? I mean, I'm getting like 1M results
>> from q1, maybe it would be better to get all results from q2 and then join
>> them in memory, or pass more than one value at a time for q2 (the VALUE
>> tag
>> allows that).
>>
>
> Without programming, there is not a way to control the execution. You can
> implement a OpExecutor and provide your own implementation of join.
>
> There are many issues such as how to know the sizes from a remote service
> and how to send data to a remote service from s1 to s2 -- VALUEs assumes
> looping back through the query engine, but does s2 allow huge SPARQL. See
> bind joins from the IBM Garlic papers.
>
> ARQ provides the basics - remote execution - but isn't a federated query
> optimizer.
>
> There is a not-yet-ready query engine, called 'quack', that provides merge
> and hash joins - only on BGPs currently but the code, in principle, is
> general.
>
> Andy
>
>
>> Cheers!
>>
>>
>> --
>> diogo patrão
>>
>>
>
--
--
diogo patrão
