HI-600: Analysis and Design of Health Information Systems

Design: Part IVProgram Design

Logical to Physical Process Models - DFD

Physical Data Flow Diagrams (DFDs)

Physical Processes

L o g i c a l P r o c e s s

CheckCustomerCredit

4.3

Physical Data Flows

Physical Data Stores

DESIGNING PROGRAMS• Designing modular, flexible and

maintainable system• Program design: top-down modular

approach:• A high-level diagram, called structure chart, is

created to illustrate the organization and interaction of the different pieces of code within the program.

• Program specifications are written to describe what needs to be included in each program module.

Structure Chart Syntax

Building the Structure Chart

Steps in Building the Structure Chart

1. Identify modules and levels2. Identify special connections3. Add couples4. Revise structure chart

Design Guidelines• Build Modules with High Cohesion• Build Loosely Coupled Modules• Create High Fan-In• Avoid High Fan-Out• Assess the Chart for Quality

Loose Coupled Modules w/ High Cohesion

Create High Fan-In and Avoid High Fan-Out

Assess the Chart for Quality

PROGRAM SPECIFICATION

SUMMARY• Moving from logical to physical process

models– Physical DFDs show implementation details

• Structure chart– The structure chart shows all of the functional components needed in

the program at a high level• Building structure chart

• Module, control connection, couples, review• Structure chart design guidelines

• Cohesion, coupling, and fan-in/fan-out

• Program specifications– Program specifications provide more detailed instructions to the

programmers.