Abstract: A general formal model for scheduling object-based distributed real-time systems is presented. The model includes absolute timing constraints to represent deadlines, periodic constraints to formulate periodicity, relative constraints to model several kinds of timed precedence relations and synchronization requirements, and consistency constraints to enforce consistent use of resources. With the proposed model, specifying the timing constraints of real-time systems on the logical and functional components of an application is possible, thus reducing the complexity of constraints specification. The rules and algorithm of converting scheduling constraints of different types are also discussed to make the existing scheduling algorithms available for the model.