This article studies characteristic properties of synchronous and asynchronous message communications in distributed systems. Based on the causality relation between events in computations with asynchronous communications, we characterize computations which are realizable with synchronous communications, which respect causal order, or where messages between two processes are always received in the order sent. It is shown that the corresponding computation

A constraint is a relation among program variables that is maintained throughout execution. Type declarations and a very general form of aliasing can be expressed as constraints. A proof system based upon the interpretation of Hoare triples as temporal logic formulas is given for reasoning about programs with constraints. The proof system is shown to be sound and relatively complete, and example program proofs are given. 1 Introduction Type declarations and aliasing relations have traditionally been thought of as unrelated concepts. However, both can be viewed as specifying properties that do not change during program execution. This view leads to a uniform method for reasoning about types and aliasing in which the usual Hoare logic triples are regarded as temporal logic formulas. Aliasing two variables x and y means they always have the same value. This is usually implemented by allocating the same memory location to x # Work supported in part by the National Science Foundation unde...

We present compositional Hoare logics for distributed systems in which communication is asynchronous via FIFO channels. The logics are proved sound and relative complete.