Nowadays, context-awareness constitutes an essential aspect for service oriented applications development. Indeed, applications are supposed to react to context changes in order to provide end-users with pertinent services. To deal with such requirement, Context-Aware Service (CAS) has emerged as an underlying software engineering paradigm for context-aware applications development. In this paper, we present a model driven approach that highlights the fundamental contextawareness challenges for CAS development. So, we first present our context metamodel based on a practical specification of the context. Then, we propose a CAS specification and metamodel and show how can Aspect Paradigm (AP) be used to fulfill service adaptation to its execution contexts. We illustrate our approach by an E-tourism motivating scenario.