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.

perl v5.28.1                                       2019-02-07                            RDF::Query::Client(3pm)