A methodology for designing and dimensioning critical complex computing systems

It is widely recognized that real-time, fault-tolerant and distributed computing technologies play a key role in the deployment of many current and future (civilian or defense) critical and complex applications. Computing systems needed to support such applications are referred to as C³ systems. Lack of a clear identification of those issues involved with designing and dimensioning C³ systems can only lead to failures, as recently demonstrated by a number of sizeable projects that have been aborted or suspended in Europe and in the USA, in various application domains. The paper describes a systems engineering methodology that, given some specification <P, p> of a particular systems engineering problem, permits to develop a specification <S, s> of a C³ system such that <S, s> probably satisfies <P, p>. It is explicitly assumed that <P, p> includes arbitrarily stringent timeliness requirements, arbitrary distribution requirements as well as arbitrarily stringent dependability requirements. Moving from <P, p> to <S, s> involves some number of design stages and one final dimensioning stage. It is shown how to verify whether every single design decision satisfies the logical part of <P, p> as well as whether a dimensioning decision satisfies the physical part of <P, p>. This methodology is fully orthogonal to formal specification methods or formal software engineering methods currently in use. It does not rest on any particular programming language either