Page 136 - DCAP405_SOFTWARE_ENGINEERING

Unit 8: Design Engineering

Notes
Figure 8.2: Types of Modules Coupling
Data coupling

Stamp coupling
Control coupling

External coupling
Common coupling

Content coupling

Notes However, if the communication takes place in the form of parameters then the
internal details of the modules are no required to be modified while making changes in
the related module.
Given two procedures X and Y, the type of coupling can be identified in them.

(a) Data coupling: When X and Y communicates by passing parameters to one another
and not unnecessary data. Thus, if a procedure needs a part of a data structure, it
should be passed just that and not the complete thing.
(b) Stamp Coupling: Although X and Y make use of the same data type but perform
different operations on them.
(c) Control Coupling (activating): X transfers control to Y through procedure calls.
(d) Common Coupling: Both X and Y use some shared data e.g. global variables. This is the
most undesirable, because if we wish to change the shared data, all the procedures
accessing this shared data will need to be modified.
(e) Content Coupling: When X modifies Y either by branching in the middle of Y or by
changing the local data values or instructions of Y.
3. Cohesion: Cohesion is the measure of the degree of functional dependence of modules.
A strongly cohesive module implements functionality that interacts little with the other
modules. Thus, in order to achieve higher interaction amongst modules a higher cohesion
is desired. Different types of cohesion are listed in Figure 8.3.
Figure 8.3: Types of Module Cohesion

Functional cohesion
Sequential cohesion

Communication cohesion
Procedural cohesion
Temporal cohesion
Logical cohesion
Coincidental cohesion

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