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, <tobyink@cpan.org>

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.