Specification of Reactive Hardware/Software Systems - Electronic ...

334 SHE Framework
11.1 Introduction
Software/Hardware Engineering is a method for the specification, analysis and design
of complex reactive systems. There is a wide gap between the aspects and problems that
are recognised during traditional (ad hoc) requirements analysis and the aspects and
problems that emerge during actual design. Figure 11.1 visualises that SHE is the bridge
between the product idea and the actual (computer aided) design and implementation of
a complex product. The method focuses specifically on the modelling of the behaviour
Product Idea Detailed Design and
Implementation
Software/hardware Engineering
Figure 11.1: SHE Bridging the Gap
of a system to be designed as a collection of collaborating concurrent objects. The starting
point for the creation of a model is a conceptual solution. The conceptual solution
basically determines the system architecture and the objects on system level. During
modelling many aspects and properties of the system come forward. These aspects and
properties cannot be found and evaluated unless modelling has been performed. The
modelling enables system level structuring and functional analysis. Specification without
system modelling can cause big problems and costs that could have been avoided.
Further it is impossible to specify the functionality of a new complex product detailed
enough without modelling. A modelling and design process always has to cope with
iterations. By taking system level design aspects into account in an early phase, the
number of iterations in a product development process can be reduced.
A specification method should contain a framework, various forms of representations,
heuristics, and a formal language. In addition, specification, analysis and design of
complex systems requires experience, skills and automated tools. Figure 11.2 visualises
these aspects. A framework gives guidance to the specification and development
process. Heuristics are rules of thumb that recommend some way of working, some
approach or some order of actions to be taken. Various representations that are used
in the framework have various purposes. Requirements that cannot be formalised (yet)
are documented in written natural language or other informal representations. The
framework integrates informal textual representations, and graphical representations
such as Architecture Structure Diagrams, Message Flow Diagrams, Instance Structure
Diagrams and Object Class Diagrams. The functional behaviour as well as the structure