OASIS provides an environment for real time multitasking and communication design, as well as an execution environment based on a safety oriented embedded real time kernel. The formal approach of real-time design avoids many difficulties: it allows implementing efficient advanced real-time functionalities without any safety loss. The concepts and methodology presented in this paper ensure the most important safety properties. Within this framework, our goal is to rely on formal and algebraic tools that can automatically bring the proof of correctness for safety-critical design issues. Such a constructive approach can easily speed up the system development by the formalization of the off-line analysis.