NAME

RDF::Flow - RDF data flow pipeline

VERSION

version 0.178

SYNOPSIS

    # define RDF sources (see RDF::Flow::Source)
    $src = rdflow( "mydata.ttl", name => "RDF file as source" );
    $src = rdflow( "mydirectory", name => "directory with RDF files as source" );
    $src = rdflow( \&mysub, name => "code reference as source" );
    $src = rdflow( $model,  name => "RDF::Trine::Model as source" );

    # using a RDF::Trine::Model as source is equivalent to:
    $src = RDF::Flow->new( sub {
        my $env = shift;
        my $uri = RDF::Flow::uri( $env );
        return $model->bounded_description( RDF::Trine::iri( $uri ) );
    } );

    # retrieve RDF data
    $rdf = $src->retrieve( $uri );
    $rdf = $src->retrieve( $env ); # uri constructed from $env

    # code reference as source (more detailed example)
    $src = rdflow( sub {
        my $uri = RDF::Flow::uri( $env );
        my $model = RDF::Trine::Model->temporary_model;
        add_some_statements( $uri, $model );
        return $model;
    });

DESCRIPTION

RDF::Flow provides a simple framework on top of RDF::Trine to define and connect RDF sources in data flow pipes. In a nutshell, a source is connected to some data (possibly RDF but it could also wrap any other forms) and you can retrieve RDF data from it, based on a request URI:

                     +--------+
    Request (URI)--->+ Source +-->Response (RDF)
                     +---+----+
                         ^
                Data (possibly RDF)

The base class to define RDF sources is RDF::Flow::Source, so please have a look at the documentation of this class. Multiple sources can be connected to data flow networks: Predefined sources exist to combine sources (RDF::Flow::Union, RDF::Flow::Pipeline, RDF::Flow::Cascade), to access LinkedData (RDF::Flow::LinkedData), to cache requests (RDF::Flow::Cached), and for testing (RDF::Flow::Dummy).

EXPORTED FUNCTIONS

By default this module only exports rdflow as constructor shortcut. Additional shortcut functions can be exported on request. The :all tag exports all functions.

rdflow

Shortcut to create a new source with RDF::Flow::Source.

cached

Shortcut to create a new cached source with RDF::Flow::Cached.

cascade

Shortcut to create a new source cascade with RDF::Flow::Cascade.

pipeline

Shortcut to create a new source pipeline with RDF::Flow::Pipeline.

previous

A source that always returns rdflow.data without modification.

union

Shortcut to create a new union of sources with RDF::Flow::Union.

LOGGING

RDF::Flow uses Log::Contextual for logging. By default no logging messages are created, unless you enable a logger. To simply see what's going on in detail, enable a simple logger:

    use Log::Contextual::SimpleLogger;
    use Log::Contextual qw( :log ),
       -logger => Log::Contextual::SimpleLogger->new({ levels => [qw(trace)]});

DEFINING NEW SOURCE TYPES

Basically you must only derive from RDF::Flow::Source and create the method retrieve_rdf:

    package MySource;
    use parent 'RDF::Flow::Source';
    use RDF::Flow::Source qw(:util); # if you need utilty functions

    sub retrieve_rdf {
        my ($self, $env) = @_;
        my $uri = $env->{'rdflow.uri'};

        # ... your logic here ...

        return $model;
    }

LIMITATIONS

The current version of this module does not check for circular references if you connect multiple sources. Maybe environment variable such as rdflow.depth or rdflow.stack will be introduced. Surely performance can also be increased.

SEE ALSO

You can use this module together with Plack::Middleware::RDF::Flow (available at at github) to create Linked Data applications.

There are some CPAN modules for general data flow processing, such as Flow and DataFlow. As RDF::Flow is inspired by PSGI, you should also have a look at the PSGI toolkit Plack. Some RDF sources can also be connected with RDF::Trine::Model::Union and RDF::Trine::Model::StatementFilter. More RDF-related Perl modules are collected at http://www.perlrdf.org/.

Research references on RDF pipelining can be found in the presentation "RDF Data Pipelines for Semantic Data Federation", more elaborated and not connected to this module: http://dbooth.org/2011/pipeline/. Another framework for RDF integration based on a pipe model is RDF Gears: https://bitbucket.org/feliksik/rdfgears/.

AUTHOR

Jakob Voß <voss@gbv.de>

COPYRIGHT AND LICENSE

This software is copyright (c) 2011 by Jakob Voß.

This is free software; you can redistribute it and/or modify it under the same terms as the Perl 5 programming language system itself.