SIOC (Semantically-Interconnected Online Communities) project is an open specification for describing communities using online discussion forums or blogs, leading to what some may term "distributed conversations". At the moment, online communities are islands that are not interlinked, and the SIOC ontology has been proposed to not only link these communities but to leverage data in ways that were previously unknown.
A revised version of our SIOC specification has recently been published at http://rdfs.org/sioc/ns# and it can be used in on its own (having a complete set of terms) or in conjunction with other RDF formats such as RSS 1.0 (and 1.1).
More info is available from http://sioc-project.org/.
While there are many (useful) classes and properties in SIOC, it can essentially be boiled down to: Users create Posts that are contained in Forums that are hosted on Sites, e.g.
Site -> host_of -> Forum -> container_of -> Post -> has_creator -> User
Posts have reply Posts, and Forums can be parents of other Forums.
The aim of this project is to create metadata from Drupal concepts such as blog, node, comment, forum, user and role using SIOC, enabling the linking of posts by topic, creator or thread. Discussions from blogs, mailing lists, forums or other discussion methods may thereby be interconnected using SIOC.