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

56 Abstraction of a Problem Domain
4.1 Introduction
4.1.1 Handling Complexity
A specification of a system is a complete description of the requirements. Furthermore
the specification must be easy to understand and therefore as simple as possible. In
practice it is very hard to achieve completeness and simplicity. During the development
process from idea to a complex product there is an overwhelming amount of aspects
and details that play a role. Designers of complex systems cannot think about all details
simultaneously. Moreover there is an overwhelming amount of relations between all
details, that must be taken into account. The huge complexity requires a plural approach
towards system specification. We distinguish the complexity of the
1. development process;
2. system’s static structure and functionality;
3. system’s temporal behaviour and other dynamic properties.
To conquer the complexity of the specification development process we need a framework
that divides the process into separate phases and activities. The decomposition
of a system into a structure of more simple collaborating subsystems conquers the complexity
of the system to be developed. So both the system design and the design process
need structure. A specification and design method offers a framework that structures
the design process and that gives a place to the various coherent representations.
By building a model of the system we can verify various system properties before the actual
implementation of the system. A model consists of many different representations.
A particular representation shows a limited amount of details. On what details the focus
is depends on the actual state of the design process and various representations used in
the framework. Highlighting of important details is achieved by abstraction. It implies
hiding of (temporarily) irrelevant details. Abstraction involves identification of the important
qualities, capabilities and properties of the phenomenon that must be modelled.
Abstraction is the key to completeness and simplicity. All necessary information must
be identified and modelled so that each phenomenon in the problem domain can be
represented adequately.
4.1.2 Problem Domain and Conceptual Solution
This chapter describes concepts for modelling of system’s static structure and functionality.
The final goal is the development of a method for the specification and design of
complex reactive hardware/software systems. Such systems offer services and communicate
with its environment. When we refer to system development we mean development
of complex mixed hardware/software systems instead of systems that are purely
implemented as software on available multipurpose hardware.
We experienced the inadequacy of existing software oriented analysis methods for system
analysis. System analysis and specification requires attention for feasibility in an