SIOC - Semantically-Interlinked Online Communities - provides the Semantic Web with a vocabulary for representing activities and contributions of online communities. However, it focuses on the state of online communities at a given time, while a number of Web application put a strong emphasis on the *dynamics* of their components and users, including microblogging, status and geolocation notification, etc. and as also testified by recent efforts on modelling activity streams. This work proposes a new module for the SIOC vocabulary designed to represent the dynamics of actions within online communities. Hence, we provide an *action-centric* view of online communities, while previous work focused on a *document-centric* or *user-centric* one. Furthermore, we align our work with related vocabularies and Web technologies --- both in use and emerging --- inside and outside the field of Semantic Web technologies.