Integrating physical and information space into applications increases application's complexity and development difficulty. In Ubiquitous environment, context collection, aggregation and notification raise complex scientific problems and new challenges. In this paper we address these challenges by proposing a conceptual context-oriented middleware architecture. We first discuss the reason to use context in ubiquitous computing, and context-oriented middleware requirements. Then we present our approach by describing a service-oriented architecture model. It provides a dynamic adaptation ability, supports multiple context models and multidomain context consumer. Finally, we discuss the benefit of our conceptual approach by describing and comparing current context middlewares.