Software Design

Requirements and -ilities

• Responsiveness

• Reliability

• Availability

• Security

• Usability

• Maintainability

• Resilience

Software Design

• How will the software work?

• Multi-level

  • Architecture: strategy
  • Detailed design: tactics

• Traceable to

  • Requirements
  • Implementation

• Comes mainly with experience, but also

  • Looking at other folks' designs
  • Reading about how design is done

Architectural and Detailed Design

• Architecture: overall block diagram of what you are building

  • Is it a pipeline? client-server? plugin architecture? file processor? database-driven? gui?
  • What sorts of constraints does the design impose?
  • How well does the architecture fit the requirements?
  • All else being equal, simpler is better

• Detailed Design: Module decomposition of what you are building

  • Usually all the way down to "units" (procedures, functions, methods)
  • Rule of 7 ± 2
  • Bottom-up vs top-down
  • All else being equal, simpler is better

Layering

• Functional layers from "back" (primitive services) to "front" (user-facing services)

• Neither too many nor too few

Client-Server Architecture

• Shared data and processing on backend

• Individualized interfaces and access on front-end

• Need not be separated by a network (but usually are)

• Compare with "Model-View-Controller pattern"

Technology Issues

• Please ignore these sections of the textbook

• In particular, please ignore the section on open source

Pseudocode

• Not necessarily every unit, but any that have anything interesting.
• Rules of Pseudocode:
  • Should be translatable to code about as fast as you can type
  • Shouldn't be code
    • English to make things clearer
    • Easy details omitted
  • 1-5 LOC per line