Query and webservices

[Diego Benna <di...@gmail.com>]

Dear community,
I'm trying the Apache API and Marmot calls to webservice.

{BASE} / SPARQL / select? Query = & output = json

as is normal, he says:
no SPARQL query specified

But how should I write the query? I tried to insert a simple select all

{BASE}/sparql/select?query=SELECT+*+WHERE+{%0D%0A++%3Fs+%3Fp+%3Fo%0D%0A}%0D%0ALIMIT+10&output=json

and I return to the classic 404

HTTP Status 400 -
type Status report
message
description The request sent by the client was syntactically incorrect.

Can you help me please? thanks

Diego Benna

Re: Query and webservices

[Sergio Fernández <wi...@apache.org>]

Hi Diego,

On 03/09/13 10:28, Diego Benna wrote:
> I'm trying the Apache API and Marmot calls to webservice.
>
> {BASE} / SPARQL / select? Query = & output = json
>
> as is normal, he says:
> no SPARQL query specified
>
> But how should I write the query? I tried to insert a simple select all
>
> {BASE}/sparql/select?query=SELECT+*+WHERE+{%0D%0A++%3Fs+%3Fp+%3Fo%0D%0A}%0D%0ALIMIT+10&output=json
>
> and I return to the classic 404
>
> HTTP Status 400 -
> type Status report
> message
> description The request sent by the client was syntactically incorrect.

Looks that your are wrongly encoding the query in your request. But 
trying to reproduce the issue, I have detected a bug (MARMOTTA-298) on 
the HTML serialization.

   http://issues.apache.org/jira/browse/MARMOTTA-298

If you were performing the request through your browser, HTML would be 
the format sent.

Please, take intro account that the 'output', 'format' or whatever query 
parameters are not part of the standard SPARQL 1.1. Protocol clients 
should use HTTP content negotiation [RFC2616] to request response 
formats that the client can consume. For further details, please check:

   http://www.w3.org/TR/sparql11-protocol/#conneg

Anyway, Marmotta, as many other SPARQL implementation, offers such 
non-official parameter for users' convenience. But the value must be a 
mimetype , not a simple label. So, instead of 'json', should be 
'application/json':

http://localhost:8080/sparql/select?query=SELECT+*+WHERE+%7B%0D%0A++%3Fs+%3Fp+%3Fo%0D%0A%7D%0D%0ALIMIT+10&output=application%2Fjson

That's why in your request 'json' was ignored, and Marmotta tried to 
return other format (HTML in that case).

For avoiding such problems, I'd recommend you to use a SPARQL client, 
which should implement all those details of the protocol. For instance, 
the Marmotta Client Library comes with a SPARQL client implementation; 
although any other implementation of the protocol (Jena, Sesame or 
whatever) should be fully compatible with Marmotta.

BTW, I already solved MARMOTTA-298 in the source code repository; so 
next builds will include the patch. Thanks for reporting the issue.

Kind regards,

-- 
Sergio Fernández