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Jakob Voß
and 3 contributors


Plack::App::RDF::Files - serve RDF data from files


Create and run a Linked Open Data server in one line:

    plackup -e 'use Plack::App::RDF::Files "app"; app(base_dir=>"/path/to/rdf")'

In more detail, create a file app.psgi:

    use Plack::App::RDF::Files;
        base_dir => '/path/to/rdf/',       # mandatory
        base_uri => 'http://example.org/'  # optional

Run it as web application by calling plackup. Request URLs are then mapped to URIs and directories to return data from RDF files as following:

    http://localhost:5000/foo  =>  http://example.org/foo
    http://localhost:5000/x/y  =>  http://example.org/x/y

In short, each subdirectory corresponds to an RDF resource.


This PSGI application serves RDF from files. Each accessible RDF resource corresponds to a (sub)directory, located in a common based directory. All RDF files in a directory are merged and returned as RDF graph. If no RDF data was found in an existing subdirectory, an axiomatic triple is returned:

    $REQUEST_URI <a <http://www.w3.org/2000/01/rdf-schema#Resource> .

Requesting the base directory, however will result in a HTTP 404 error unless option index_property is enabled.

HTTP HEAD and conditional GET requests are supported by ETag and Last-Modified-Headers (see Plack::Middleware::ConditionalGET).



Mandatory base directory that all resource directories are located in.


The base URI of all resources. If no base URI has been specified, the base URI is taken from the PSGI request.


An array of RDF file types, given as extensions to look for. Set to ['rdfxml','nt','ttl'] by default.


By default a HTTP 404 error is returned if one tries to access the base directory. Enable this option by setting it to 1 or to an URI, to also serve RDF data from the base directory. By default http://www.w3.org/2000/01/rdf-schema#seeAlso is used as index property, if enabled.


Optional code reference that maps a local part of an URI to a relative directory. Set to the identity mapping by default.


Optional namespaces for serialization, passed to RDF::Trine::Serializer.


Optional Unicode Normalization form (NFD, NFKC, NFC, NFKC). Requires Unicode::Normalize.


call( $env )

Core method of the PSGI application.

The following PSGI environment variables are read and/or set by the application.


The requested URI as string or URI object.


The RDF::Trine::Iterator that will be used for serializing, if psgi.streaming is set. One can use this variable to catch the RDF data in another post-processing middleware.


An hash of source filenames, each with the number of triples (on success) as property size, an error message as error if parsing failed, and the timestamp of last modification as mtime. size and error may not be given before parsing, if rdf.iterator is set.


RDF serialization format (See Plack::Middleware::Negotiate). Supported values are ttl, nt, n3, json, and rdfxml.

If an existing resource does not contain triples, the axiomatic triple $uri rdf:type rdfs:Resource is returned.

files( $env )

Get a list of RDF files (as hash reference) that will be read for a given request, given as PSGI environment.

The requested URI is saved in field rdf.uri of the request environment. On success returns the base directory and a list of files, each mapped to its last modification time. Undef is returned if the request contained invalid characters (everything but a-zA-Z0-9:.@/- and the forbidden sequence ../ or a sequence starting with /), or if called with the base URI and index_property not enabled.

headers( $files )

Get a response headers object (as provided by Plack::Util::headers) with ETag and Last-Modified from a list of RDF files given as returned by the files method.


app( %options )

This shortcut for Plack::App::RDF::Files->new can be exported on request to simplify one-liners.


Use Plack::Middleware::Negotiate to add content negotiation based on an URL parameter and/or suffix.

See RDF::LinkedData for a different module to serve RDF as linked data. See also RDF::Flow and RDF::Lazy for processing RDF data.

See http://foafpress.org/ for a similar approach in PHP.


Copyright Jakob Voss, 2014-

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