The pervasiveness of software in contemporary society means that software designers are increasingly responsible for our:

• Quality of Life
• Productivity
• Economic Well-Being
• Health

• The Definition:
  • Software design is the process of specifying the nature and composition of a software system that satisfies client needs and desires, subject to constraints.
• An Important Question:
  • What's a system?

System

A set of entities, their attributes, and the relationships between them.

Entities

The components of the system that are known/observed.

Attributes

The properties of the entities (i.e., the external manifestations of the way the objects are known or observed).

Relationships

The bonds that link objects and attributes

• An Important Observation:
  • We can define systems in an enormous number of ways depending on the level of detail (abstraction) used
• The Level of Detail is Relative To:

  Environment

  The set of all other systems (also known as the context and the domain)

  Subsystems

  Parts of the whole which display a richness of interrelationships

  Elements/Atoms

  The smallest parts of the system (i.e., black boxes)

• Software product design is the process of specifying software product features, capabilities and interfaces to satisfy client needs and desires.
• Software engineering design is the process of specifying programs and sub-systems, and their constituent parts and workings, to meet software product specifications.

• The Logical Process:
  • Identify Goals, Objectives and Constraints
  • Generate Alternatives
  • Evaluate Alternatives
  • Select an Alternative
• Two Aspects of the Logical Process:
  • Analysis (to understand the problem)
  • Resolution (to "solve" the problem)

1. Identify the important data (i.e., describe things in terms of their parts). For example, a car has wheels, doors, an engine, ...
2. Identify the processes that manipulate these data
3. Elaborate (i.e., decompose the data into subordinate data)

1. Identify the processes/procedures/functions (i.e., describes things in terms of their processes). For example, a car can move, uses gasoline, ...
2. Identify the data that are manipulated by these processes
3. Elaborate (i.e., specify inputs/outputs and reduce into subordinate processes)

• The Idea:
  • Start by thinking about things and the way they are used
  • Describe things in terms of their responsibilities
  • Example: A car runs, carries people, ...
• The Resulting Object-Oriented Paradigm:
  • Focus on understanding real-world concepts
  • This involves the natural combination of data and processes