Static Type Checking and Deadlock Prevention in
           Systems Based on Asynchronous Message Passing

                 Christof Peter and Franz Puntigam
    Technische Universität Wien, Institut für Computersprachen
        Argentinierstraße 8, A-1040 Vienna, Austria, Europe
	   e-mail: {christof,franz}@complang.tuwien.ac.at

Most strong, static type models were developed for centralized, sequential
systems. However, static type checking may even be more useful in
distributed systems because in these systems it is extremely difficult to
restore a consistent system state after a type error has occurred. Type
models for concurrent systems shall be more expressive than those for
sequential systems. But for more expressive types it is more difficult to
perform static type checking. We show a hierarchy of four increasingly
expressive levels of type models and discuss the possibility of static
type checking and static deadlock prevention for them.