MODULE COHESION

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COHESION

It's a measure which defines the level of inter dependability among the elements of a module.

The greater the cohesion the better the program design will be.

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1.COINCIDENTAL COHESION

Low cohesion.There is no dependency btw x and y.

It occurs when modules are grouped together for no reason at all.

Elements contribute to activities with no meaningful relationship to one another

It is difficult to understand and maintain with strong possibilities of causing side effects every time the module is modified.

use customer record.

display customer record.

calculate total show.

read transaction record.

return transaction record.

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LOGICAL COHESION

There is some dependency btw x and y and x controls y.

Therefore logical cohesion occurs in modules that contain instructions that appear to be related bcoz they fall into the same logical class or functions.

Module display record.

use record type,record.

If record type is student then

display student record.

Else If record type is staff then

display staff record.

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TEMPORAL COHESION

At a time many operations.

Both x and y must perform around the same time.

Element are involved in activities that are related in time,commonly found in initialization and termination modules.

set counter to zero.

open student file.

clear error message variables.

initialize arrays.

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PROCEDURAL COHESION

Performs one by one operation.

Elements are related only by sequence otherwise the activities are unrelated.

Similar to sequential cohesion except for the fact that elements are unrelated.

write out record.

Read in record.

numeric fields with zeroes.

return in record.

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COMMUNICATIONAL COHESION

Same input same output.

Elements contribute to activities contain same input or same output data.

If all the functions of the module refer to or update the same data structure.

Eg:

The set of functions defined as an array,modules are grouped together bcoz they access the same I/P or O/P devices.

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SEQUENTIAL COHESION

Output of first operation becomes the input of second operation.

x output some data which forms the input of y.

This is the reason for them to be contained in the same procedure.

Eg: get input

validate input

sort input data

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FUNCTIONAL COHESION

Inter dependability among elements is high.

Many operations in one function.

X and Y are part of a single functional task.

This is the best cohesion method.

All elements of a module related to the performance of a single function.

If diff. elements of a module co operate to achieve a single function.

Eg: A module containing all of the functions required to manage employ payroll exhibits functional cohesion.