Ch10-Program Design

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Systems Analysis and DesignSystems Analysis and Design
5th Edition5th Edition
Chapter 10. Program DesignChapter 10. Progra...

Chapter 10 Outline
Moving from logical to physical
process models.
Designing programs.
Structure chart.
Program specif...

INTRODUCTION
 Program design – Analysts determine what programs will
be written and create instructions for the programme...

MOVING FROM LOGICAL TO PHYSICAL
PROCESS MODELS
The analysis phase focuses on logical data
flow diagrams which do not cont...

The Physical Data Flow Diagram
The physical DFD contains the same
components as the logical DFD, and the same
rules apply...

(cont’d)
Steps to Create the Physical Data
Flow Diagram
© Copyright 2011 John Wiley & Sons, Inc. 10-6

(cont’d)
© Copyright 2011 John Wiley & Sons, Inc. 10-7
Example of Physical DFD

DESIGNING PROGRAMS
Analysts should create a design of a
maintainable system that is modular
and flexible.
 Analysts can ...

(cont’d)
Using a Top-Down Modular Approach
© Copyright 2011 John Wiley & Sons, Inc. 10-9

(cont’d)
 Program design in the top-down modular
approach:
- A high-level diagram, called structure chart, is
created to ...

STRUCTURE CHART
The structure chart is an Important program
design technique that help the analyst design
the program.
I...

(cont’d)
Structure Chart Example
© Copyright 2011 John Wiley & Sons, Inc. 10-12

Syntax of Structure Chart
© Copyright 2011 John Wiley & Sons, Inc. 10-13

(cont’d)
© Copyright 2011 John Wiley & Sons, Inc. 10-14

(cont’d)
Revised structure chart example
© Copyright 2011 John Wiley & Sons, Inc. 10-15

Building the Structure Chart
Process models are used as the start point for
structure charts.
There are three basic kind...

(cont’d)
© Copyright 2011 John Wiley & Sons, Inc. 10-17

Transaction Structure
There are two basic arrangement, or
structures, for combining modules.
The transaction structure c...

(cont’d)
© Copyright 2011 John Wiley & Sons, Inc. 10-19

Transform Structure
The transaction structure has a control
module that calls several subordinate modules
in sequence aft...

Steps in Building the Structure Chart
1. Identify modules and levels.
2. Identify special connections.
3. Add couples.
4. ...

Design Guidelines
High quality structure charts result in
programs that are modular, reusable,
and easy to implement.
Me...

Build Modules with High Cohesion
Cohesion refers to how well the lines
of code within each module relate to
each other.
...

(cont’d)
There are various types of cohesion.
Functional cohesion – all elements of the
modules contribute to performing...

(cont’d)
© Copyright 2011 John Wiley & Sons, Inc. 10-25

(cont’d)
© Copyright 2011 John Wiley & Sons, Inc. 10-26
Cohesion Decision Tree

(cont’d)
Factoring is the process of
separating out a function from one
module into a module of its own.
Factoring can m...

Build Loosely Coupled Modules
Coupling involves how closely modules are
interrelated.
Modules should be loosely coupled....

Create High Fan-In
Fan-in describes the number of control
modules that communicate with a
subordinate.
 A module with hi...

Avoid High Fan-Out
A large number of subordinates
associated with a single control
should be avoided.
The general rule o...

(cont’d)
Examples of Fan-in and Fan-out
© Copyright 2011 John Wiley & Sons, Inc. 10-31

Assess the Chart for Quality
Check list for structure chart quality
© Copyright 2011 John Wiley & Sons, Inc. 10-32

PROGRAM SPECIFICATION
 Program Specifications are documents that include
explicit instructions on how to program pieces o...

(cont’d)
© Copyright 2011 John Wiley & Sons, Inc. 10-34
Program specification form

(cont’d)
Pseudocode Example
© Copyright 2011 John Wiley & Sons, Inc. 10-35

SUMMARY
 Moving from logical to physical process models.
- Physical DFDs show implementation details.
 Structure chart.
...

Copyright 2011 John Wiley & Sons, Inc.
All rights reserved. Reproduction or translation of this work
beyond that permitted...

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