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
<
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.