Abstract. SIOC provides the Semantic Web with a vocabulary for representing the state of online communities at a given time. However, a number of web application put a strong emphasis on the dynamics of their components and users, as testified by the recent normalisation efforts on activity streams. This work proposes a module for the SIOC vocabulary designed to represent the dynamics of SIOC represented online communities, centred on the notion of action. We link this work to related vocabularies and technologies, both in use and emerging, inside and outside the field of Semantic Web technologies.