MCS-014 Unit 6 Modular and Structured Design

7/22/2019 MCS-014 Unit 6 Modular and Structured Design

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MCS014 System Analysis And Design

Unit6Modular And Structured Design

By

Kirit A. D.

(MBA, PMP, ITIL, MCTS, SSBB)


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Properties Of Design

Verifiability

Traceability

Completeness Consistency

Efficiency

Simplicity

Modular

AndStructuredDesign


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Design Principles

Problem Partitioning

Abstraction

Top Down Design Bottom Up Design

Modular

AndStructuredDesign


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Structure Chart

Depicts the modular organization of an

information system

A structure chart graphically shows the

way the components of a program or a

system are related

Modular

AndStructuredDesign


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Hierarchy of a Structure Chart

System

Get X Make Y

Get W Make X

Modular

AndStructuredDesign


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Symbols

Module AModule A

(Superordinate)

Module B(Subordinate)

Symbol of ModuleData Couples

(Data Communication)

Control Flag

(Data Being Communicated)

Module A(B & C Called Repeatedly)

Module B Module CModular

AndStructuredDesign


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Symbols

Module A

Module B

Predefined Module

Module A

Module B is Embedded In Module A

Subordinate Modules Are Called On Condition

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Reading Structure Chart

System

Get Marks A Get Marks B Make Result R Put Result R

Read

Marks A

Validate

Marks A

Read

Marks B

Validate

Marks B

MA MB

MA

MBR

R

MA VMAMA MB MB VMB MA : Marks AMB : Marks B

VMA : Valid MA

VMB : Valid MB

Modular

AndStructu

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Modularity

Modularity is a single attribute of software

that allows a program to be intellectually

manageable

Increases the design clarity

Decomposing a system into smaller

components that can be coded separately

Goals of Design

Coupling

CohesionModular

AndStructu

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Goal of Design

Design said to be fine only when, read, code andmaintained easily.

The design of the system should be module based

Each module controls the functions of a suitablenumber of subordinate modules at the nexthierarchical level

Communication among the module should bekept minimum

Keep the size as low as possible

The coding of modules should be genericModular

AndStructu

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Goal of Design - Guidelines

System should be divided in to as manyrelatively independent modules as possible(factoring)

Superordinate module should control notmore than 7 (thumb rule) subordinatemodule

Dependency level should be as low as

possible

Usually minimum 50 to maximum 100 linesof code per moduleM

odular

AndStructu

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CouplingData Coupling

Prepare Salary

(Superordinate)

Calculate Salary

(Subordinate)

Salary

AmountStatusSalary

Details

EOF

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AndStructu

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CouplingStamp Coupling

Prepare Pay slip

Format Pay

slip

Employee

Record

Employee

Record

Formatted

Pay SlipSalarySalary AmountSalaryDetails

Calculate Total

Salary

Data

Structure

Modular

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CouplingControl

Prepare Pay slip

Calculate Total Salary

Write Salary is Seven Days Late

Modular

AndStructu

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CouplingCommon

Global data areas are used by the multiple

modules

A variable can be declared at appropriate

level so that it is treated as global variable

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CouplingContent

Used only when non of the discussed are

possible

Drawback isone module can access the

data inside another module and alter it

Most of the high level languages dont

support content coupling

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Cohesion

The degree to which a module conforms itself to the performance of a single task

Module will perform single task which leads to larger degree of portability

We can directly plug in the module in an application which requires the performance

of this task

Since it performs single task, minimum or no need to know the internal function of

any other module

There are seven types of cohesion

Functional Cohesion

Sequential Cohesion

Communicational Cohesion

Procedural Cohesion

Temporal Cohesion

Logical Cohesion

Coincidental Cohesion

Modular

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Cohesion

Functional

If every instruction in the module is related to a

single task

The name of the module will usually indicatethe task that is performed by it eg. Print Grade

Cards, Generate Payslips

Sequential

Product purchase order->prepare shipping

order-> update inventory-> update accounts

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AndStructu

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Communication Cohesion

Its like sequential cohesion except the fact that

there is not restriction on the sequencing pattern

Find Employee Details

Employee Record Employee Name

Employee Designation

Employee Service

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Functionally Cohesion



Employee Designation



Employee Salary

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Procedural Cohesion

Any module not functionally cohesive is difficultto maintain

Sequence of instruction is important.

Sequence cannot be changed arbitrarily

E.g. Pick the course material from MPDD

Check the enrolment number on the Hall ticket

Attend counseling sessions at study Centre

Submit assignments at study Centre Above example shows, instructions are not related

to each other in terms of sequence.Modular

AndStructu

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Temporal Cohesion

Instructions in a module are related toeach other only by flow of control and aretotally unrelated to their sequence.

Eg. Delete duplicate data from inventory file

Reindex inventory file

Backup of inventory file Nothing common but, kind of cleanup

activityModular

AndStructu

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Logical Cohesion

Instructions in the form of sets

Bare minimum relation between various instructions

Execution takes place in terms of set of instructions

rather than individual instruction Not a good type of cohesion

Difficult to maintain logically cohesive module

Eg.

Study in home

Study in library

Study in gardenModular

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Coincidental Cohesion

No relationship between the instructions

This is worse type of cohesion among the

discussed

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AndStructu

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Questions ?

Thank You

Documents

MCS-014 Unit 6 Modular and Structured Design