Basic Design Principles

When designing a system's architecture we try to follow the principles outlined below.

Abstraction

Abstraction is achieved in the following areas:

procedural abstraction
data abstraction
control abstraction

Refinement

Stepwise refinement is a way to tame the details and complexity of the final design.

Modularity

A modular design minimises the system's complexity and thereby the development cost and the number of possible errors. A good design method should provide:

modular decomposability
modular composability
individual modular understandability
modular continuity (in changes: minimize the modules affected by any change)
modular protection: a problem in one part should not create problems in others

Cohesion

A design should bring closely together parts that exhibit a high measure of cohesion. We can distinguish the following ordered types of cohesion:

coincidental cohesion
logical cohesion
temporal cohesion
procedural cohesion
communicational cohesion
sequential cohesion
functional cohesion

Coupling

On the other hand, a design should avoid coupling between parts. We can distinguish the following ordered types of coupling:

data coupling
stamp coupling (copy of a part)
control coupling
common coupling
external coupling
content coupling

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