Software Engineering

1
Software Engineering

• Design Principles
• Lecture 8

2
Overview

• Goal To produce a model that can be built!
• Problems
• Good techniques still evolving and changing
• Hard to measure design quality
• Often start with poor requirements documents
• One of the 3 main technical activities

3
Design Models

• Data Design
• Architecture Design
• Interface Design
• Procedural design

4
Design goals

• Implement all requirements from analysis (and not
  additional ones!!!)
• Provide a good basis for coders and testers
• Provide a complete picture of the software --
  from a data, functional, and behavioral
  perspective

5
Structural design

• Hierarchical
• Modular
• Data and procedural abstractions
• Should lead to modules
• Should lead to clear interfaces

6
Principles

• No tunnel vision
• Traceable to analysis
• Take advantage of previous experiences
• Uniformity and integration
• Make future changes easier
• Design ! code. And code ! design
• Review at all levels

7
Concepts

• Abstraction
• Refinement
• Modularity
• S/W Architecture
• Control hierarchy
• Structural partitioning
• Data Structures

8
Concepts

• S/W procedures
• Information hiding

9
Modular Design

• Functional independence
• cohesion vs. coupling
• heuristics
• reduce coupling
• minimize fan-out/ maximize fan-in at depths
• keep scope of effect within the scope of control
• module interfaces -- KISS, consistent
• controlled entry to modules