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.

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.