Abstract. We present the data modeling concepts of Tricia, an opensource Java platform used to implement enterprise web information systems as well as social software solutions including wikis, blogs, file shares and social networks. Tricia follows a data model driven approach to system implementation where substantial parts of the application semantics are captured by domain-specific models (data model, access control model and interaction model). In this paper we give an overview of the Tricia architecture and development process and present the concepts of its data model: plugins, entities, properties, roles, mixins, validators and change listeners are motivated and described using UML class diagrams and concrete examples from Tricia projects. We highlight the benefits of this data modeling framework for application developers (expressiveness, modularity, reuse, separation of concerns) and show its impact on userrelated services (content authoring, integrity checking, link managemen...