NAME
   RDF::Query::Client - get data from W3C SPARQL Protocol 1.0 servers

SYNOPSIS
    use RDF::Query::Client;

    my $query = RDF::Query::Client
                  ->new('SELECT DISTINCT ?s WHERE { ?s ?p ?o . }');

    my $iterator = $query->execute('http://example.com/sparql');

    while (my $row = $iterator->next) {
       print $row->{s}->as_string;
    }

DESCRIPTION
 Constructor
   `new ( $sparql, \%opts )`
       Returns a new RDF::Query::Client object for the specified $sparql. The
       object's interface is designed to be roughly compatible with
       RDF::Query objects, though RDF::Query is not required by this module.

       Options include:

       UserAgent - an LWP::UserAgent to handle HTTP requests.

       Unlike RDF::Query, where you get a choice of query language, the query
       language for RDF::Query::Client is always 'sparql'.
       RDF::TrineShortcuts offers a way to perform RDQL queries on remote
       SPARQL stores though (by transforming RDQL to SPARQL).

 Public Methods
   `execute ( $endpoint, \%opts )`
       $endpoint is a URI object or string containing the endpoint URI to be
       queried.

       Options include:

       *   UserAgent - an LWP::UserAgent to handle HTTP requests.

       *   QueryMethod - 'GET', 'POST', 'PATCH' or undef (automatic).

       *   QueryParameter - defaults to 'query'.

       *   AuthUsername - HTTP Basic authorization.

       *   AuthPassword - HTTP Basic authorization.

       *   Headers - additional headers to include (hashref).

       *   Parameters - additional GET/POST fields to include (hashref).

       *   ContentType - 'application/sparql-query',
           'application/sparql-update' or 'application/x-www-form-urlencoded'
           (default).

       Returns undef on error; an RDF::Trine::Iterator if called in a scalar
       context; an array obtained by calling `get_all` on the iterator if
       called in list context.

   `discover_execute( $resource_uri, \%opts )`
       Experimental feature. Discovers a SPARQL endpoint relevant to
       $resource_uri and then calls `$query->execute` against that. Uses an
       LRDD-like method to discover the endpoint. If you're publishing data
       and want people to be able to find your SPARQL endpoint automatically,
       the easiest way is to include an Link header in HTTP responses:

        Link: </my/endpoint>; rel="http://ontologi.es/sparql#endpoint"

       Change the URL in the angled brackets, but not the URL in the rel
       string.

       This feature requires the HTTP::LRDD package to be installed.

   `get ( $endpoint, \%opts )`
       Executes the query using the specified endpoint, and returns the first
       matching row as a LIST of values. Takes the same arguments as
       `execute`.

   `as_sparql`
       Returns the query as a string in the SPARQL syntax.

   `useragent`
       Returns the LWP::UserAgent object used for retrieving web content.

   `http_response`
       Returns the last HTTP Response the client experienced.

   `error`
       Returns the last error the client experienced.

 Security
   The `execute` and `get` methods allow AuthUsername and AuthPassword
   options to be passed to them for HTTP Basic authentication. For more
   complicated authentication (Digest, OAuth, Windows, etc), it is also
   possible to pass these methods a customised LWP::UserAgent.

   If you have the Crypt::SSLeay package installed, requests to HTTPS
   endpoints should work. It's possible to specify a client X.509 certificate
   (e.g. for WebID authentication) by setting particular environment
   variables. See Crypt::SSLeay documentation for details.

BUGS
   Probably.

   Please report any you find here:
   <https://rt.cpan.org/Dist/Display.html?Queue=RDF-Query-Client>.

SEE ALSO
   *   RDF::Trine, RDF::Trine::Iterator

   *   RDF::Query

   *   LWP::UserAgent

   *   <http://www.w3.org/TR/rdf-sparql-protocol/>

   *   <http://www.w3.org/TR/rdf-sparql-query/>

   *   <http://www.perlrdf.org/>

AUTHOR
   Toby Inkster, <[email protected]>

COPYRIGHT AND LICENSE
   Copyright (C) 2009-2013 by Toby Inkster

   This library is free software; you can redistribute it and/or modify it
   under the same terms as Perl itself.

DISCLAIMER OF WARRANTIES
   THIS PACKAGE IS PROVIDED "AS IS" AND WITHOUT ANY EXPRESS OR IMPLIED
   WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF
   MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE.

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