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Introduction

Term Definition​

  • Design: Deliberative, purposive planning
  • Engineering: Skillful or artful contrivance applying scientific and mathematical principles
  • Craft: skilled occupation
  • Art: user of skill, taste, and imagination in the production of aesthetic objects.

Software Design​

The process of building a program while satisfying a problem's functional requirements and not violating its non-functional constraints.

Two stages​

  • Architectual Design: the process of identifying and assigning the responsibility for aspects of behavior to various modules or components of a software.
  • Detailed design: the process of specifying the behavior of each of the system components that you've identified during architectural design.

Design Notations for algorithms​

  • Pseudo code
  • structured programming
  • Flow chart
  • Decision tables

Approaches' aspects​

  • Design method: a particular way of viewing the problem.
    • OOD
    • Structure design
    • Role based design
  • design representation
  • how that design is going to be validated.

Design issues​

  • top down, bottom up, inside up?
  • Procedures, functions or nouns, objects.
  • conceptual integrity vs cooperative development.
  • trades-off between Long term maintainability and short term schedule
  • What tools to use?

How to validate the design?​

  • Independence of validators
  • Dependence on design methods
  • On-going versus after-the-fact

Design Concepts​

  • Conceptual integrity
    • Coupling: the extent two components depends on each other for successful execution.
    • Cohension: The extent that the module or component has a single purpose or function.
  • Information hiding: eencapsulating the capabilities that a particular module has behind an abstract interface.
  • Abstraction and Refinement
    • Arrays, structs, record, objects
    • class hierarchy and generation

Aesthetics​

  • Beauty, elegance, resolve to wholeness, harmony and radiance.
  • It takes a lot of time and energy to come up with an elegant solution that looks quite simple on the surface, but really satisfies the complex requirements.

Design philosophy​

Piete En related software design to four important philosophers.

  1. Descartes - analytic geometry.
  2. Marx - social processes and classes
  3. Martin Heidegger - tools
  4. Wittgenstein - the concept of language games, inventing a vocabulary for a particular problem.