Real-time and embedded systems are becoming increasingly important nowadays and touch a large range of activities. However, due to their tight integration with the physical world, these systems come with a large variety of hardware platforms, making software integration difficultly achievable. To circumvent this problem, new programming abstractions are needed to handle efficiently complexity and heterogeneity of these systems. Component-Based Software Engineering (CBSE) has emerged as an excellent candidate to achieve greater software understanding, reuse and reliability. Through our research work, we have designed a composition language that provides abstractions and means to facilitate design, analysis and validation of real-time systems. In this paper, we present the theory, which underpins the language.