Provided by: librdf-linkeddata-perl_1.940-1_all bug


       Plack::App::RDF::LinkedData - A Plack application for running RDF::LinkedData


       Version 1.940


         my $linkeddata = Plack::App::RDF::LinkedData->new();
         my $rdf_linkeddata = $linkeddata->to_app;

         builder {
            enable "Head";
                 enable "ContentLength";
                 enable "ConditionalGET";


       This module sets up a basic Plack application to use RDF::LinkedData to serve Linked Data,
       while making sure it does follow best practices for doing so. See the README for quick
       start, the gory details are here.


   Quick setup for a demo

       It is possible to make it run with a single command line, e.g.:

         PERLRDF_STORE="Memory;path/to/some/data.ttl" plackup -host localhost script/linked_data.psgi

       This will start a server with the default config on localhost on port 5000, so the URIs
       you're going serve from the file data.ttl will have to have a base URI

       There is also a "LOG_ADAPTER" that can be set to any of Log::Any::Adapter to send logging
       to the console. If used with Log::Any::Adapter::Screen, several other environment
       variables can be used to further control it.

       Using perlrdf command line tool

       A slightly longer example requires App::perlrdf, but sets up a persistent SQLite-based
       triple store, parses a file and gets the server with the default config running:

         export PERLRDF_STORE="DBI;mymodel;DBI:SQLite:database=rdf.db"
         perlrdf make_store
         perlrdf store_load path/to/some/data.ttl
         plackup -host localhost script/linked_data.psgi

       To configure the system for production use, create a configuration file
       "rdf_linkeddata.json" that looks something like:

               "base_uri"  : "http://localhost:3000/",
               "store" : {
                          "storetype"  : "Memory",
                          "sources" : [ {
                                       "file" : "/path/to/your/data.ttl",
                                       "syntax" : "turtle"
                                      } ]

               "endpoint": {
                       "html": {
                                "resource_links": true
               "expires" : "A86400" ,
               "cors": {
                         "origins": "*"
               "void": {
                         "pagetitle": "VoID Description for my dataset"
               "fragments" : { "fragments_path" : "/fragments" }

       In your shell set

         export RDF_LINKEDDATA_CONFIG=/to/where/you/put/rdf_linkeddata.json

       Then, figure out where your install method installed the <linked_data.psgi>, script, e.g.
       by using locate. If it was installed in "/usr/local/bin", go:

         plackup /usr/local/bin/linked_data.psgi --host localhost --port 3000

       The "endpoint"-part of the config sets up a SPARQL Endpoint. This requires the
       RDF::Endpoint module, which is recommended by this module. To use it, it needs to have
       some config, but will use defaults.

       It is also possible to set an "expires" time. This needs Plack::Middleware::Expires and
       uses Apache "mod_expires" syntax, in the example above, it will set an expires header for
       all resources to expire after 1 day of access.

       The "cors"-part of the config enables Cross-Origin Resource Sharing, which is a W3C
       Recommendation for relaxing security constraints to allow data to be shared across
       domains. In most cases, this is what you want when you are serving open data, but in some
       cases, notably intranets, this should be turned off by removing this part.

       The "void"-part generates some statistics and a description of the dataset, using
       RDF::Generator::Void. It is strongly recommended to install and run that, but it can take
       some time to generate, so you may have to set the detail level.

       Finally, "fragments" add support for Triple Pattern Fragments, a work-in-progress, It is a
       more lightweight but less powerful way to query RDF data than SPARQL. If you have this, it
       is recommended to have CORS enabled and required to have at least a minimal VoID setup.

       Note that in some environments, for example if the Plack server is dynamically configured
       and/or behind a proxy server, the server may fail to bind to the address you give it as
       hostname. In this case, it is wise to allow the server to bind to any public IP address,
       i.e. set the host name to

   Details of the implementation
       This server is a minimal Plack-script that should be sufficient for most linked data
       usages, and serve as a an example for most others.

       A minimal example of the required config file is provided above. There is are longer
       examples in the distribution, which is used to run tests. In the config file, there is a
       "store" parameter, which must contain the RDF::Trine::Store config hashref. It may also
       have a "base_uri" URI and a "namespace" hashref which may contain prefix - URI mappings to
       be used in serializations. Certain namespace, namely RDF, VoID, Hydra, DC Terms and XML
       Schema are added by the module and do not need to be declared.

       Note that this is a server that can only serve URIs of hosts you control, it is not a
       general purpose Linked Data manipulation tool, nor is it an implementation of Linked Data
       Platform or the Linked Data API.

       The configuration is done using Config::ZOMG and all its features can be used.
       Importantly, you can set the "RDF_LINKEDDATA_CONFIG" environment variable to point to the
       config file you want to use. See also Catalyst::Plugin::ConfigLoader for more information
       on how to use this config system.

       The following documentation is adapted from RDF::LinkedData::Apache, which preceded this

       ·   ""

           Will return an HTTP 303 redirect based on the value of the request's Accept header. If
           the Accept header contains a recognized RDF media type or there is no Accept header,
           the redirect will be to "", otherwise to
           "". If the URI has a foaf:homepage or foaf:page
           predicate, the redirect will in the latter case instead use the first encountered
           object URI.

       ·   ""

           Will return a bounded description of the "" resource in an
           RDF serialization based on the Accept header. If the Accept header does not contain a
           recognized media type, RDF/XML will be returned.

       ·   ""

           Will return an HTML description of the "" resource
           including RDFa markup, or, if the URI has a foaf:homepage or foaf:page predicate, a
           301 redirect to that object.

       If the RDF resource for which data is requested is not the subject of any RDF triples in
       the underlying triplestore, the /page and /data redirects will not take place, and a HTTP
       404 (Not Found) will be returned.

       The HTML description of resources will be enhanced by having metadata about the predicate
       of RDF triples loaded into the same triplestore. Currently, only a "rdfs:label"-predicate
       will be used for a title, as in this version, generation of HTML is done by

   Endpoint Usage
       As stated earlier, this module can set up a SPARQL Endpoint for the data using
       RDF::Endpoint. Often, that's what you want, but if you don't want your users to have that
       kind of power, or you're worried it may overload your system, you may turn it off by
       simply having no "endpoint" section in your config. To use it, you just need to have an
       "endpoint" section with something in it, it doesn't really matter what, as it will use
       defaults for everything that isn't set.

       RDF::Endpoint is recommended by this module, but as it is optional, you may have to
       install it separately. It has many configuration options, please see its documentation for

       You may also need to set the "RDF_ENDPOINT_SHAREDIR" variable to wherever the endpoint
       shared files are installed to. These are some CSS and Javascript files that enhance the
       user experience. They are not strictly necessary, but it sure makes it pretty!
       RDF::Endpoint should do the right thing, though, so it shouldn't be necessary.

       Finally, note that while RDF::Endpoint can serve these files for you, this module doesn't
       help you do that. That's mostly because this author thinks you should serve them using
       some other parts of the deployment stack. For example, to use Apache, put this in your
       Apache config in the appropriate "VirtualHost" section:

         Alias /js/ /path/to/share/www/js/
         Alias /favicon.ico /path/to/share/www/favicon.ico
         Alias /css/ /path/to/share/www/css/

   VoID Generator Usage
       Like a SPARQL Endpoint, this is something most users would want. In fact, it is an even
       stronger recommendation than an endpoint. To enable it, you must have RDF::Generator::Void
       installed, and just anything in the config file to enable it, like in the SYNOPSIS

       You can set several things in the config, the property attributes of RDF::Generator::Void
       can all be set there somehow. You can also set "pagetitle", which sets the title for the
       RDFa page that can be generated. Moreover, you can set titles in several languages for the
       dataset using "titles" as the key, pointing to an arrayref with titles, where each title
       is a two element arrayref, where the first element is the title itself and the second is
       the language for that title.

       Please refer to the RDF::Generator::Void for more details about what can be set, and the
       "rdf_linkeddata_void.json" test config in the distribution for example.

       By adding an "add_void" config key, you can make pass a file to the generator so that
       arbitrary RDF can be added to the VoID description. It will check the last modification
       time of the file and only update the VoID description if it has been modified. This is
       useful since as much of the VoID description is expensive to compute. To use it, the
       configuration would in JSON look something like this:

               "add_void": { "file": "/data/add.ttl", "syntax": "turtle" }

       where "file" is the full path to RDF that should be added and "syntax" is needed by the
       parser to parse it.

       Normally, the VoID description is cached in RAM and the store ETag is checked on every
       request to see if the description must be regenerated. If you use the "add_void" feature,
       you can force regeneration on the next request by touching the file.

   Read-write support
       Some recent effort has gone into experimental write support, which for this module has the
       implications that a boolean option "writes_enabled" that configures the application for
       writes. This is also meant as security, unless set to true, writes will never be
       performed. To support writes, a "class" option can be set with a class name, which can be
       instantiated to replace RDF::LinkedData. See RDF::LinkedData::RWHypermedia for more on


       Please contact the author if this documentation is unclear. It is really very simple to
       get it running, so if it appears difficult, this documentation is most likely to blame.


       You would most likely not need to call these yourself, but rather use the
       "linked_data.psgi" script supplied with the distribution.

           This is the only method you would call manually, as it can be used to pass a hashref
           with configuration to the application.

           Will be called by Plack to set the application up.

           Will be called by Plack to process the request.

       "auth_required ( $request )"
           A method that returns true if the current request will require authorization.

       "check_read_operation ( $request )"
           A method that will return true if the current request is a pure read operation.


       Kjetil Kjernsmo, "<>"


       Copyright 2010, 2011, 2012, 2013, 2014, 2015, 2016, 2017, 2018 Kjetil Kjernsmo

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