Smart environments are spaces that interact with users taking into account their needs and preferences. Systems that manage these environments need to manipulate the context for interacting in a suitable way with users. One big challenge for creating a smart environment is to deal with context dynamicity. Ideally, these computer-supported environments must detect relevant events to forecast future situations and to act proactively to mitigate or eliminate situations related to specific user's needs. This paper proposes a framework for providing extensible, reactive and proactive behavior in Smart Environment systems. The focus of the present work is related to a specific class of Smart Environments: an Ambient Assisted Living. In this sense we define a framework and illustrate practical aspects of the use of framework by describing a home-care scenario in which the system observes the behavior of the user, as the time goes by, and detects relevant situations and acts reactively and proactively for preserving user health condition.