A Web application capable of parsing and displaying license information embedded in both well-formed and ill-formed Web pages has been developed. It supports the following means of embedding license information: Dublin Core metadata, RDFa, RDF/XML linked externally or embedded (utilising the data URL scheme) using the link and a elements, and RDF/XML embedded in a comment or as an element (the last two being deprecated). This functionality has been proven by unit testing. The source code of a Web page can be uploaded or pasted by a user, there is also a possibility to provide a URI for the Web application to analyse it. The software has been written in Python and uses the Pylons Web Framework and the Genshi toolkit. Should you be willing to test this Lynx-friendly application, please visit its Web site.

The Web application itself uses a library called “libvalidator”, which in turn is powered by cc.license (a library developed by Creative Commons that returns information about a given license), pyRdfa (a distiller that generates the RDF triples from an (X)HTML+RDFa file), html5lib (an HTML parser/tokenizer), and RDFLib (a library for working with RDF). The choice of this set of tools has not been obvious and the library had undergone several redesigns, which included removing the code that employed encutils, XML canonicalization, µTidylib, and the BeautifulSoup. The idea of using librdf, librdfa, rdfadict has been abandoned. The source code of both the Web application (licensed under the GNU Affero General Public License version 3 or newer) and its core library (licensed under the GNU Lesser General Public License version 3 or newer) is available through the Git repositories of Creative Commons.

In contrast to the contents of the original proposal, the following goals have not been met: traversal of special links, syndication feeds parsing, statistics, and cloning the layout of the Creative Commons Web site. However, these were never mandatory requirements for the Web application. It is also worth noting that the software has been written from scratch, although a now-defunct metadata validator existed. Nevertheless, the development does not end with Google Summer of Code — these and several new features (such as validation of multimedia files via liblicense and support for different language versions) are planned to be added, albeit at a slower pace.

After the test period, the validator will be available under http://validator.creativecommons.org/.

The source code is located in two dedicated git repositories. The first being validator, which contains the source code of the Web application based on Pylons and Genshi. The second repository is libvalidator, which hosts the files that constitute the core library that the project will utilise. This is the component that the development focuses on right now.

The purpose of the aforementioned library is to parse input files, scan them for relevant license information, and output the results in a machine-readable fashion. More precisely, its workflow is the following: parse the file and associated RDF information so that a complete set of RDF data is available, filter the results with regard to license information (not only related to the document itself, but also to other objects described within it), and return the results in a manner preferable for the usage by the Web application.

pyRdfa seems to be the best tool for the parsing stage so far. It handles the current recommendation for embedding license metadata (namely RDFa) as well as other non-deprecated methods: linking to an external or embedded (using the “data” URL scheme) RDF files and utilising the Dublin Core. The significant lacking is handling of the invalid direct embedding of RDF/XML within the HTML/XHTML source code (as an element or in a comment) and this is resolved by first capturing all such instances using a regular expression and then parsing the data just as external RDF/XML files.

Once the RDF triples are extracted, one can use SPARQL to narrow the results just to the triples related to the licensed objects. Both librdf and rdflib support this language. Moreover, the RDF/XML related to the license must be parsed, so that its conditions (permissions, requirements, and restrictions) are then presented to the user.

The library takes advantage of standard Python tools such as Buildout and nose. When it is completed, the project will be all about writing a Web application that will serve as an interface to libvalidator.

Er, maybe not. Fourty-five minutes, five marker colors and multiple digressions later, I had the following diagram of life as it is today.

Life sucks.

Asheesh joined us and we started talking about how we can make this better. The above, while eminently sucky, has grown up during my time at Creative Commons. All those decisions made sense at the time, but in aggregate we’ve got lots of duplicated code, a branch of code named the gradually-increasing-sanity-branch which doesn’t (I take the blame for that one), and plenty of unnecessary complexity. Half an hour later, we had mapped out The Glorious Future®:

A little simpler, huh? And the “future” diagram shows all the functionality of the present, plus three packages not displayed on the original diagram. Our immediate goal in moving in this direction is the completion of cc.license (labeled as “cc.licenze” in the diagrams to distinguish it from the existing implementation) which will replace the existing XSLT processing using for issuing licenses and wraps the RDF (which is the canonical representation of the licenses anyway). We’ll also manage to dramatically reduce the number of svn:externals we use, which is good since we’re moving away from Subversion for some projects. My goal is to get this upgrade done as soon as possible so we can focus on things that are actually interesting instead of our own infrastructure.