TROPES is an object-based knowledge representation system, containing three important intertwined features: constraints, composite objects and tasks. Constraints provide a declarative means to define and maintain relations between objects. The part-whole relation profits by constraints for sharing attribute values between a composite object and its components. The task model benefits from composite objects for task modeling and from classification and instantiation mechanisms for task execution; it also uses constraints to propagate input and output data from one task to another.