the contexts base and, on the other hand, to enable calling the PAM services. The components of the three layers of the PAM are built around profile and context meta models that are generic enough to be adapted to a wide range of applications and that are open to integrate specific knowledge not included in the initial modeling. All PAM components are developed in conformance with the meta models. Thus, all messages addressed to the PAM should respect the meta models format. The rest of this section is devoted to the detailed description of the main services. Section 10.3.1 presents offline services: context discovery and contextualization. Section 10.3.2 describes online services: binding, matching and query reformula- tion. Finally, Section 10.3.3 introduces various instantiations of the PAM. 10.3.1 Offline Services Offline services are used to define profiles, contexts, as well as their relationships. Definitions are either done manually by human designers or automatically by software processes, for example, by exploiting log files. Personalization Paradigm in Service Delivery Platforms 10.3.1.1 Context Discovery The role of this service is to identify, for each user, regular contexts within which he interacts with the system. For instance, the system can record the fact that each morning, at work, a user reads news about Java programming whereas at home, in the evening, the same user consults blogs about board games. If such observations are recurrent, the contexts morning_at_work and evening_at_home can be identi- fied. An overview of this service is given in Figure 10.6. The context discovery service takes as input a trace of the user activity. This activity is generally available as log files on an application server. By analyzing these logs, the service has to point out relevant contexts for each user with their descrip- tion. Before performing this task, log files have to be preprocessed and cleaned. The discovery of contexts from the cleaned logs necessitates regrouping each user action in relevant clus