Modelling Functional Design in MBSE

This article addresses the problem of placing functional decomposition in Model Based Systems Engineering (MBSE) on a formal mathematical basis in order to support the development of effective mathematical models of digital twins. This has necessitated the re-examination of a number of concepts used within functional decomposition, in-cluding the representation of open systems, the specification of user requirements, the definition of inputs and outputs and the meaning of systems engineering “functions”. This resulted in the proposal to consider interactions of the system with its environ-ment rather than input/output requirements and to correctly identify the systems en-gineering concept of “function” with the mathematical concept of “functional”. By doing this we have developed a unified approach to modelling in MBSE that integrates a number of existing approaches, including Wymore’s, DEVS and Linear Systems Theory. This results in a mathematical formalism that results in a systems model that traceably satisfies the user requirements.