I've submitted this project paper to the Triplification Challenge 2009, it did not make it into the proceedings (but so far it seems, that even the winners are not part of). Someone may find it interesting, here you are.

Authors: Michael Haschke and Sebastian Dietzold

Abstract: DokuWiki is a popular and widely used wiki engine, keeping all the data directly in the file system. DokuSIOC integrates the SIOC ontology within DokuWiki and it provides meta data about the wiki documents, using RDF/XML views.

Keywords: Semantic Web, DokuWiki Plugin, SIOC

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The Semantic Web extends the original Web with machine processable semantics [Berners-Lee et al., 2001] and it provides technologies and standards to integrate, relate and combine machine readable data. In contrast to the original Web, the Semantic Web describes not only interlinked documents but rather interoperable data which can “be shared and reused across application, enterprise, and community boundaries.”¹⁾ Semantic annotations as well as data interoperability are good reasons to enhance existing applications in order to connect them with the Semantic Web and get their data out of their silos.

DokuWiki is a wiki [Leuf and Cunningham, 2001] engine, “mainly aimed at creating documentation of any kind. It is targeted at developer teams, workgroups and small companies. All data is stored in plain text files – no database is required.”²⁾ In DokuWiki, wiki pages can have sub pages, in this case a wiki page is a namespace as well.

DokuWiki is widely used³⁾, known in literature [Badger, 2006] and even nominated for the Top 10 wiki engines at Cunningham's WikiWikiWeb⁴⁾. In addition to this, DokuWiki is the technical foundation for the research project ICKE 2.0 (Integrated Collaboration & Knowledge Environment, [ Fuchs-Kittowski and Hüttemann, 2009]), so we assume a broad user base with many installations and target content for our triplification project.

The SIOC (Semantically-Interlinked Online Communities) Core Ontology specifies the main concepts and properties for describing information from online communities, e.g. wikis and weblogs, on the Semantic Web [Berrueta et al., 2007]. As other vocabularies, SIOC is extensible and can be combined with other models as well.

In Section 2, I discuss how DokuWiki and its users benefit from the possibility to export data using the SIOC model. The implementation with DokuWiki is described in Section 3 and then in Section 4, I will do a conclusion and a an outlook what steps could be the next.

Leaving the closed data silo and providing interoperable data are the main benefits of using Semantic Web technologies, offering more possibilities to aggregate content – beside Atom and RSS – is a nice side effect. To connect user spaces and content in DokuWiki instances from currently unconnected user profiles is another basic benefit.

As always we are discussing the technological openness, not the undermining of the rights management. Beside the DokuWiki view of the wiki pages via browser you can currently access the page content via file system or raw text export. These possibilities are lacking semantically defined meta data, e.g. creator, contributors and relations between wiki pages, to name a few. Other applications cannot process this wiki data without a specific importer. The SIOC plugin opens the wiki instance to third party applications via Linked Data [Berners-Lee, 2006] and the usage of the well defined SIOC vocabulary. A consuming agent is now able to process the data without any knowledge of DokuWikis internal structure.

Currently, DokuWiki provides RSS and Atom feeds. The feed content depends on the configuration created by the administrator of the DokuWiki instance. It could be the current version of recently added pages or maybe only the differences between revisions. With the SIOC plugin it is possible to start at any point and aggregate the content part by part, including page relations and revision links. As an example figure 1 shows aggregated content in the semantic data wiki OntoWiki [Auer et al., 2006], which was fetched by OntoWiki's Linked Data wrapper.

If a person contributes content to one or more than one DokuWiki instances, it is possible to link from the person's homepage to the various wiki pages. Those HTML links are untyped relations between web sites and need to be updated with the creation of every new wiki page. The SIOC plugin simplifies this process by providing SIOC profiles for user accounts. Now a person only needs to add the resource URIs of those accounts to the personal FOAF (Friend of a Friend, [Brickley and Miller, 2007]) profile to declare her own content. In particular, wiki pages could be retrieved automatically.

The DokuWiki architecture is extensible by action plugins, which can subscribe their methods as event listeners to DokuWiki events. The DokuWiki documentation⁵⁾ gives detailed information how to do it. In this section, we discuss the implementation of DokuSIOC⁶⁾.

DokuWiki handles internal user identifiers and profiles, e.g. to provide access control and rights management. It does not provide any URI for a user. In order to do create such a user space, DokuSIOC offers a way to configure a DokuWiki namespace, where user identifiers can be used as sub pages. This hook provides profile sites for user accounts, e.g. http://eye48.com/dokuwiki/doku.php?id=user:haschek.

A DokuWiki URI can stand for different resources. The profile example may describe the user (sioc:User), a wiki page (sioct:WikiArticle), a container for sub content (sioc:Container) and even the special wiki container (sioct:Wiki) if the user page is used as DokuWiki starting page. The SIOC plugin adds a type parameter to distinguish exactly between the resources, for example the URI for the user account is now http://eye48.com/dokuwiki/doku.php?id=user:haschek&type=user, an example for a wiki article is http://eye48.com/dokuwiki/doku.php?id=en&type=post.

DokuWiki saves all content and its meta data to flat files. This kind of data store prevents the usage of already existing projects like Triplify [Auer et al., 2009] to publish content as RDF. DokuSIOC uses the DokuWiki export action to provide a meta document which describe the requested resource. The Linked Data approach is used to interlink between related resources, e.g. containers of wiki pages, backlinks and contributing users. Linked Data wrappers now can request further documents to access more data. To generate the XML serialisation of the SIOC documents, DokuSIOC uses the PHP exporter provided by the SIOC project⁷⁾. The meta document for the article example is http://eye48.com/dokuwiki/doku.php?do=export_siocxml&id=en&type=post.

DokuSIOC provides two different ways to direct client applications to the meta data. Firstly, DokuSIOC adds a meta link to the header of the DokuWiki HTML view,

<link type="application/rdf+xml" rel="meta" href="http://[...]/doku.php?do=export_siocxml&amp;id=en&amp;type=post" />''

Clients can follow this link for fetching the RDF/XML document with meta data about the currently shown HTML document. In addition to this, DokuSIOC supports content negotiation as discussed in [Ayers and Völkel, 2008]. If the client requests http://eye48.com/dokuwiki/doku.php?id=en&type=post as application/rdf+xml, the plugin will send a 303 (see other) HTTP status code and forwards to the location of the RDF export view.

In Section 2 we introduced DokuWiki and why it is worth to have an RDF export there. The main benefits for DokuWiki and its users has been described in Section 2, mainly it is about accessible data. Afterwards we presented an implementation as DokuWiki plugin and showed, how it works. Additionally the plugin offers the feature to ping http://pingthesemanticweb.com/ when content is created or modified.

In a future version, we want to enhance important DokuWiki plugins like discussion and tagging in order to support RDF export too as well as to add more meta data to the SIOC profiles, e.g. by automatically linking DokuWiki articles with DBpedia [Auer et al., 2008] resources.

Finally we hope to convince the DokuWiki community and the project maintainers for packaging DokuSIOC in the default DokuWiki distribution.

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