Almost all context-aware systems have two indispensable components - context provider and context consumer. The former is responsible for supplying diverse context information about users and environments, while the later makes use of context information in building context-aware applications. The diversity of context information from heterogeneous context suppliers to different consumers justifies the need for a generic re-usable middleware to manage context data flow from low-level providers to high-level consumers. As a first step, we propose a declarative quality-aware context middleware specification language. It contains four types of descriptors, namely, point descriptors, connector descriptors, constraint descriptors, and quality descriptors. Through the context middleware specification, context acquisition, integration, and transformation patterns from suppliers to consumers, as well as associated functionality and non-functionality requirements and constraints, can be uniformly declared.