Structured Design

Structured Design

1. Top-down approach

DFDs with automation boundaries.

System flowcharts, structure charts, pseudocodo
2. The automation of system boundary

Partitions data flow diagram processes into manual processes and automated systems.

Processes can be inside or outside of boundary.

Data flows can be inside and outside of boundary.

a. Crossing the system boundary represent inputs and outputs of system.

b. Crossing boundaries between programs represent program-to-program communication.

3. The system flowchart

Representation of various computer programs, files, database and associated manual processes that make up complete system.

4. The structure chart

a) Describe functions and subfunctions of each part of system.
b) Show relations between modules of a computer system.

Developing a structure chart:

a. Transaction analysis: uses system flow charts and event table inputs upper-level modules developed first
Identifies each transaction supported by the program.

b. Transform analysis: use DFD fragments for inputs into outputs
Computer program transforms inputs into outputs
Chart shave input, calculate and output subtrees.

Evaluating the quality of a structure chart:

a. Module coupling: measure of how module is connected to other modules in program and the goal is to be loosely coupled.

b. Module cohesion: measure of internal strength of module and goal is to be highly cohesive.

5. Three-layer design: view layer, business logic layer , and data layer.