Combining traditional personalization techniques with novel knowledge representation paradigms, such as the ontology-based approach proposed in the Semantic Web field, is a challenging task. Personalization is a difficult problem when dealing with multimedia content and information retrieval, where context is increasingly acknowledged to be a key notion in order to make proper sense of user needs. This work focuses on contextualization within personalization in a multimedia environment. Towards that scope, we propose a novel contextual knowledge modeling scheme, and an approach for the dynamic, contextual activation of semantic user preferences to better represent user interests in coherence with ongoing user activities, e.g. in an interactive retrieval process. The application of this methodology is demonstrated using two user scenarios, and the performance results of a preliminary experiment are shown.