Page 137 - DCAP405_SOFTWARE_ENGINEERING

Software Engineering

Notes The direction of the arrow in Figure 8.3 indicates the worst degree of cohesion to the best degree
of cohesion. The worst degree of cohesion, coincidental, exists in the modules that are not
related to each other in any way. So, all the functions, processes and data exist in the same
module.
Logical is the next higher level where several logically related functions or data are placed in the
same module.
At times a module initializes a system or a set of variables. Such a module performs several
functions in sequence, but these functions are related only by the timing involved. Such cohesion
is said to be temporal.
When the functions are grouped in a module to ensure that they are performed in a particular
order, the module is said to be procedurally cohesive. Alternatively, some functions that use the
same data set and produce the same output are combined in one module. This is known as
communicational cohesion.
If the output of one part of a module acts as an input to the next part, the module is said to have
sequential cohesion. Because the module is in the process of construction, it is possible that it
does not contain all the processes of a function. The most ideal of all module cohesion techniques
is functional cohesion. Here, every processing element is important to the function and all the
important functions are contained in the same module. A functionally cohesive function performs
only one kind of function and only that kind of function.
Given a procedure carrying out operations A and B, we can identify various forms of cohesion
between A and B:

(a) Functional Cohesion: A and B are part of one function and hence, are contained in the same
procedure.
(b) Sequential Cohesion: A produces an output that is used as input to B. Thus they can be a
part of the same procedure.
(c) Communicational Cohesion: A and B take the same input or generate the same output.
They can be parts of different procedures.
(d) Procedural Cohesion: A and B are structured in the similar manner. Thus, it is not advisable
to put them both in the same procedure.

(e) Temporal Cohesion: Both A and B are performed at moreover the same time. Thus, they
cannot necessarily be put in the same procedure because they may or may not be performed
at once.
(f) Logical Cohesion: A and B perform logically similar operations.
(g) Coincidental Cohesion: A and B are not conceptually related but share the same code.

Information Hiding: In computer science, information hiding is the principle of segregation of
the design decisions in a computer program that are most likely to change, thus protecting other
parts of the program from extensive modification if the design decision is changed. The protection
involves providing a stable interface which protects the remainder of the program from the
implementation (the details that are most likely to change).
Written another way, information hiding is the ability to prevent certain aspects of a class or
software component from being accessible to its clients, through an explicit exporting policy
and through reliance on the short form as the primary vehicle for class documentation.

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