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The Use of the ADA Language for Programming a Distributed System

1980; Elsevier BV; Volume: 13; Issue: 1 Linguagem: Inglês

10.1016/s1474-6670(17)65159-0

2589-3653

Valerie Downes, S. J. Goldsack,

Formal Methods in Verification

This paper discusses the programming of networks of co-operating computers in a control environment. The computers in the systems considered are weakly coupled, having no shared store and communicating by messages over a network. Such a system could be programmed in Ada, or any other language, as a set of separate machines, with the communication explicitly handled by input/output procedures. However, this would not be in the spirit of a distributed system, involving a very rigid structure, decided when the program was written. A system for control should preferably be written as a complete program, in a uniform language, regarding the manner in which it is executed, in a single machine or in a network of smaller machines, as an implementation detail. Being designed for the programming of embedded systems, Ada has many features which are appropriate for this purpose. There do seem, however, to be a number of areas where work is needed to resolve difficulties which will arise in practice. This paper attempts to identify these problem areas and offer possible solutions to some of them. It is suggested that it is useful to recognize a logical module for such programs which encapsulates groups of tasks which it is necessary to confine to a single processor node, due to timing or resource sharing constraints. These modules can be programmed in Ada as tasks, nevertheless they represent a sufficiently distinct abstraction to deserve separate nomendature; here they are referred to as zones.