Current applications are often forced to filter the richness of datasources in order to reduce the information noise the user is subject to. We consider this aspect as a critical issue of applications, to be factorized at the data management level. The Context-ADDICT system, leveraging on ontology-based context and domain models, is able to personalize the data to be made available to the user by "context-aware tailoring". In this paper we present a formal approach to the definition of the relationship between context (represented by an appropriate context model) and application domain (modeled by a domain ontology). Once such relationship has been defined, we are able to work out the boundary of the portion of the domain relevant to a user in a certain context. We also sketch the implementation of a visual tool supporting the application designer in this modeling task