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

11.2 SHE Context and Phases 335
Informal
representations
(text, graphical)
Framework Method Heuristics
Formal
Language
Experience,
skills
Tools
Figure 11.2: Elements of an Analysis Method
of a system are formalised by a description in the language POOSL. The final goal of
the method is to be able to give a consistent and validated specification that is feasible
and implementable. Simulation and formal verification of the behaviour will enable in
depth examination of various system properties.
In the previous chapters we presented all elements and notations that are used in the
method. In this chapter we present the framework of the method, a recapitulation
of the various representations, their purpose, and the relations between the various
representations. Aspects of the practical use of the method, heuristics and guidelines
for the modelling process are presented partially in this chapter and partially in the next
chapter (Chapter 12).
11.2 SHE Context and Phases
The input for modelling with the SHE method is information about the product to be
designed. This information is called the Initial Requirements Description. The use of the
method results in a simplified final detailed design and implementation process. Figure
11.3 shows the phases and milestones of the SHE method in a system specification and
design project. SHE has two phases, marked by a milestone in between (milestone 2).
These phases are the realisation of an Essential Specification and an Extended Specification.
11.2.1 Initial Requirements Description
The starting point for the creation of an essential specification is a completed Initial
Requirements Description (milestone 1). This description contains:
a requirements list;