A non-formal motivation and description is given of ADL-d, a graphical design technique for parallel and distributed software. ADL-d allows a developer to construct an application in terms of communicating processes. The technique distinguishes itself from others by its rigid orthogonal approach to communication modeling, which is advantageous in many areas. Without being committed to one particular design method, ADL-d as a technique can be used from the early phases of application design through phases that concentrate on algorithmic design, and final implementation on some target platform. The authors discuss and motivate all ADL-d components, including recently incorporated features such as support for connection-oriented communication, and support for modeling dynamically changing communication structures.

DNP (dynamic networks of processes) is a variant of the language introduced by Kahn and MacQueen [11, 12]. In the language it is possible to create new processes dynamically. We present a complete, formal denotational semantics for the language, along the lines sketched by Kahn and MacQueen. An informal explanation of the formal semantics is also given.

In [SIAM J. Comput., 7 (1978), pp. 70–90] Cook defines the operational semantics of a programming language in the following way; a function is introduced which takes a program R and a state $\sigma $ and yields a possibly infinite row of intermediate states as a result. This row is meant to be the trace resulting from executing program R starting in state $\sigma $. This function is characterized by a number of equations. However it is not immediately clear whether these equations have a solution. In this paper we show for a simple language, the most sophisticated feature of which is that it has parameterless procedures,that the corresponding equations have a unique solution. The techniques used here can also be applied to other languages described in the same way, for instance to the language in Cook’s paper.