I. INTRODUCTION

While new paradigms, tools and web services introduced by the Social Web (such as blogs, wikis, tagging practices) are now widely accepted in both public and scientific communities, these tools generally act as independent data silos; hence, interoperability between applications is a complex issue. The SIOC project 1 aims at solving this by providing a comprehensive data model (as well as related tools and applications) based on Semantic Web technologies [1] in order to represent online communities and their activities in an homogenous way.

The SIOC project consists of two main parts:

• The SIOC Ontology, composed of a Core ontology and different modules; • A set of applications, for both producing and consuming SIOC data, constantly evolving based on the user needs and implementations.

II. THE SIOC ONTOLOGY

The SIOC Ontology is composed of a Core ontology and a set of modules, focusing on the ease of integration of SIOC in existing applications by Web developers. With an emphasis on standard Semantic Web technologies since its beginning, the whole ontology has been designed using RDF(S)/OWL. A comprehensive overview of the SIOC ontology is provided in [2].

A. SIOC Core Ontology

Main classes and properties in the SIOC ontology2 are shown in Figure 1. While relatively small and simple, this model is yet powerful enough to represent the content produced and exchanged within online communities. For instance, a Forum represents a space in which discussion happen (not necessarily a bulletin board, in spite of its name, but for example as a weblog), and contains different Posts, written by Users. The following example then describes that Alice has created a post in a particular forum (i.e. an area of discussion) and that Bob replied to it -as follows (using the N3 notation -prefixes omitted). In order to represent more abstract containers (such as a personal information space), more general Container and Space classes can be used.

:post a sioc:Post ; sioc:has_creator :alice ; sioc:has_container :forum ; sioc:has_reply :reply . :forum a sioc:Forum . :reply a sioc:Post ; sioc:has_creator :bob . :alice a sioc:User . :bob a sioc:User . Other properties and classes exist in the ontology, for instance properties to represent previous and next versions of an item, which can be used when representing Wikis.

It is worth noticing that each sioc:User is actually related to the Agent class (from the FOAF3 -Friend Of A Friend [3] -ontology), and that sioc:User can be consequently associated with both software agents and human users. Hence, SIOC can be used to represent communication between bots on the Social Web (e.g. on IRC using the SIOC-IRClog project 4 ) and then enable a machine-readable description of communities of agents interacting together on social websites. Moreover, another link between FOAF and SIOC is that the social networking aspect can be represented using FOAF (by foaf:knows), while SIOC can be used to represent aspects of relationships inside the community, e.g. a user following another (on microblogging services) can be expressed by the sioc:follows property.

B. SIOC Modules

Several SIOC modules have been defined to extend the available terms and to avoid making the SIOC Core Ontology too complex and unreadable. SIOC has 4 ontology modules: Access, Argumentation, Services and Types 5 .

III. STATUS AND UPDATE OF SIOC

Since the goal of SIOC is to provide interoperability between communities on the Social Web, one way to evaluate its success is to consider its uptake on the Web. To illustrate the amount of SIOC data on the Web, according to the PingTheSemanticWeb (PTSW) service 7 on June 2009 there were 132'475 URIs which contain data described using the SIOC ontology 8 .

In addition to the uptake in terms of number of documents, SIOC is now widely accepted as a core ontology to describe Social Web communities using Semantic Web technologies, alongside with FOAF. Hence, the use of SIOC is suggested by the Yahoo! SearchMonkey developer documentation 9 (SIOC 4 http://irc.sioc-project.org/about.html 5 Information about SIOC modules: http://rdfs.org/sioc/spec/#sec-modules 6 http://rdfs.org/sioc/swan 7 http://pingthesemanticweb.com 8 The full amount of SIOC information on the Web is larger than described here as PTSW indexes only a part of available RDF data. 9 http://developer.yahoo.com/searchmonkey/smguide/profile vocab.html data being indexed by SearchMonkey to improve presentation of search results) and by various best practices documents describing data publishing on the Semantic Web such as [5].

Various SIOC-enabled applications have been created 10 , forming a food-chain (Figure 2) that includes data exporters for Web 2.0 platforms and services (e.g. Drupal 11 , WordPress, Flickr, etc.), tools for indexing of distributed data, and browser and visualization applications, allowing users to consume SIOC data from various sources in an integrated way.

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