Abstract
The rapid evolution of software paradigms, wireless technologies and mobile devices induced the emergence of new applications called context-aware services oriented applications. Such applications provide appropriate services or relevant information to the user or other applications to perform a specific task. An important challenge in such applications development process is context modeling and reasoning. Ontology based models presents the most promising instrument for context modeling and offers possibility of applying ontology reasoning techniques. the aim of context reasoning is converting low-level context to highlevel context in order to provide costumized services to users. In this paper, we present an architecture for the development of context aware services based on ontologies. We also highlight our context metamodel and discuss about reasoning process for e-health systems.