NAME

RDF::LinkedData::RWHypermedia - Experimental read-write hypermedia support for Linked Data

SYNOPSIS

This module extends RDF::LinkedData, and you would most likely not call this module directly, but rather configure it using the tools that RDF::LinkedData provides.

DESCRIPTION

This module is an experiment to manipulate Linked Data using human and machine readable hypermedia descriptions. The intention is to have messages that are intuitive to newcomers, so that they can get going using it without much training. For now, it has very basic, prototypical functionality, but it represents an implementation of an idea that the author thinks is worth discussing.

To use it, please see the README of RDF::LinkedData. To that configuration, add the two options

"class" : "RDF::LinkedData::RWHypermedia",
"writes_enabled" : 1,

and set a username and password, like this for now:

"credentials" : {
        "username" : "testuser",
        "password" : "sikrit" },

Also, hypermedia is on by default, ensure that it isn't turned off.

Then, start the server as you would with Plack::App::RDF::LinkedData.

Behaviour

In addition to the behaviour documented in Plack::App::RDF::LinkedData, this module will add a predicate to any data about a certain resource that tells the user it can check a certain URI to see if it may edit the resource description. If the user goes there, they will be challenged to authenticate, and if authorized (currently, an authenticated user has all privileges), they will be shown how to edit the resource description.

Extending the examples of Plack::App::RDF::LinkedData, http://host.name/rdf/example/data points to http://host.name/rdf/example/controls, which when authorized, shows the users triples like

<http://host.name/rdf/example/data> hm:canBe hm:replaced .

thus encouraging the user to replace the data with a new resource description. The idea is further that hm:replaced can be defined with protocol-specific semantics, for example that in HTTP, it means that the user may PUT data in an RDF format to the URL.

TODO

The idea is also that this approach should be extended to support different identity (WebID is an obvious candidate) and authorization regimes (I started implementing the W3C access control lists ontology, but found it more urgent to get the hypermedia ideas coded). Eventually, I think this approach should reach parity with the Linked Data Platform, but without an out-of-band specification.

METHODS AND ATTRIBUTES

response

This module wraps RDF::LinkedDatas response method, taking control of write methods and data to be added to the response for controls and data. The latter is achieved by also wrapping the private _content method.

user

Can be read or set to the username of the logged in user.

is_logged_in

Indicates whether a user is logged in.

log_out

Log out user.

add_rw_pointer ($hypermedia_model, $uri)

A method that will add a triple to the data page for the given URI to the model building the hypermedia of the response.

credentials_ok, unauthorized, authenticator, credentials

Methods that deals with authentication and authorization. This part is really not stable, just for demo purposes at present. The last is currently a hashref so that a configured username and password can be passed to the authenticator.

FEEDBACK

Since this is a prototype, I hope this will spark discussion. There are some discussion items inline in the code. They include how and what data should be merged to a given URL, what the responses should look like.

Apart from comments to my email, the IRC channels irc://irc.perl.org/#perlrdf and irc://irc.freenode.net/#swig are good forums for discussing this topic.

I will be blogging about this work at http://kjetil.kjernsmo.net/category/technology/hypermedia/.

Bugs

Please report any bugs to https://github.com/kjetilk/p5-rdf-linkeddata-rwhypermedia/issues.

Author

Kjetil Kjernsmo <kjetilk@cpan.org>.

COPYRIGHT AND LICENCE

This software is copyright (c) 2017, 2018 by Kjetil Kjernsmo.

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