e the data sparsity prob- lem which may be increased when considering context in the recommenda- tion process [12]. As a consequence of the separation of profiles and contexts, different privacy rules can be applied. In some applications, user profiles may be more sensitive than user contexts (e.g., anonymity), while in others, contexts may be more sensitive (e.g., user location or itinerary). Besides, this separability allows applications to be only aware of profiles or contexts or of both. The achievement of such recommender systems needs a concrete instantiation of different PAM services presented in Section 10.3. To simplify the understanding of our approach, we present, hereafter, some definitions of the main concept we manip- ulate, and then, an example scenario that combines PAM services to provide users with context-aware recommendations. Details on each service are presented later. 10.4.2.2.1 Main Concepts This section provides an informal definition of the concepts that will be used in the following sections. User Profile: A user profile provides an extensive definition of the preferences that a user has in a given domain of interest. Concretely, a profile is a set of prefer- ences, each being an (attribute, value) couple rated by the user or the RS on the basis of the user's actions. Active User: In an RS, an active user is the one for whom recommendations are calculated. Service Delivery Platforms Context: A context is the description of the features characterizing the environ- ment within which users interact with an RS. As for the profile, the context is a set of contextual attributes, acquired from user log files. Active context: It is the context within which the active user interacts with an RS. It is also called current context. Contextualized Profile: It is a set of mappings that relate a subset of profile pref- erences to the context in which they are defined (i.e., the context in which recom- mended items are rated). Operational Profile: It is a runtime binding of a contextualized profile to 