  In this paper, we introduce a novel situation aware approach to improve a
context based recommender system. To build situation aware user profiles, we
rely on evidence issued from retrieval situations. A retrieval situation refers
to the social spatio temporal context of the user when he interacts with the
recommender system. A situation is represented as a combination of social
spatio temporal concepts inferred from ontological knowledge given social
group, location and time information. User's interests are inferred from past
user's interaction with the recommender system related to the identified
situations. They are represented using concepts issued from a domain ontology.
We also propose a method to dynamically adapt the system to the user's
interest's evolution.
