The TYPESET-10 Message Exchange Facility: a case study in systemic design

This paper describes the design considerations which led to the successful implementation of an interprocess communication mechanism, named the Message Exchange Facility (MX). The software implemented Message Exchange Facility provides services analogous to those of the hardware bus. It is the central link that binds a collection of synergistic asynchronous processes into a single systemic entity, the Digital Equipment Corporation's TYPESET-10 computerized newspaper production system. The peculiar functional constraints and requirements -dictated by TYPESET-10's specialized runtime environment- confronted us with a very difficult, and at the same time highly challenging, design problem. In this paper, the emphasis is placed on the decision making process leading from the statement of the problem to a specific technical solution.