Chapter 9 - Program Design

Program Design

Process of determining what programs to write, giving instructions to programmers, and organizing code components into a system

Physical DFD

Diagram showing how system processes, data flows, and data stores are implemented

Implementation References

Details added to a DFD showing how components are implemented

Human-Machine Boundary

Line separating automated (system) processes from manual (human) processes

System-Related Components

Additional data stores, flows, and processes specific to system implementation

Data Flow Updates

Modifications to data flows to include system-related elements

Metadata (CASE Repository)

Updated information about DFD components with implementation details

Top-Down Modular Approach

Breaking down a system into smaller modules from general to specific

Structure Chart

Diagram showing organization and interaction of program modules

Sequence

Order in which modules are executed

Selection

Condition determining when a module is executed

Iteration

Repetition of a module

Module

Logical unit or component of a program

Loop

Structure indicating repetition of a module

Conditional Line

Indicates modules are executed based on conditions

Control Module

Higher-level module that directs other modules

Subordinate Module

Module controlled or called by a higher-level module

Library Module

Reusable, standardized module

Data Couple

Passing of data between modules

Control Couple

Passing of control signals or messages between modules

Off-Page Connector

Symbol indicating continuation of a diagram on another page

On-Page Connector

Symbol indicating continuation within the same page

Afferent Processes

Processes that provide input to the system

Central Processes

Core processes performing main system functions

Efferent Processes

Processes that produce outputs

Transaction Structure

Structure where modules handle separate transactions

Transform Structure

Structure where modules transform input into output sequentially

Identify Modules and Levels

Process of defining modules from DFD and organizing hierarchy

Special Connections

Loops and conditional lines representing repetition or conditions

Couples

Data or control links between modules

Structure Chart Revision

Process of refining the structure chart for completeness

Cohesion

Degree to which elements within a module are related

High Cohesion

Each module performs a single, focused task

Factoring

Breaking a module into smaller, more focused modules

Coupling

Degree of interdependence between modules

Loose Coupling

Modules are minimally dependent on each other

Fan-In

Number of modules calling a single module

Fan-Out

Number of modules controlled by one module

Structure Chart Quality

Evaluation based on cohesion, coupling, fan-in, fan-out, and modularity

Program Specification

Document with detailed instructions for coding programs

Program Information

Basic details such as module name, purpose, programmer, and language

Structured Programming

Code executed in a predefined sequence

Event-Driven Programming

Code executed in response to events

Inputs and Outputs

Data entering and leaving a program

Pseudocode

Structured English used to outline program logic