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 relevent 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, <tobyink@cpan.org>

COPYRIGHT AND LICENSE
    Copyright (C) 2009-2011 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.