Software Methodologies

Posted on May 19, 2022

Two types: Plan-driven and Agile.
All processes involve:

  • Software specification - What the software should do
  • Design and implementation - How it should be organised and implemented
  • Validation - Checking it does what the customer asked
  • Evolution - Changing the software over time

Software specification

  • Define which services are required and limitations of the system
  • Idea: Create a document that anyone could use to build the system

Stages of requirements engineering:

  • Feasibility study - Produce feasibility report
  • Requirements, elicitation and analysis - Looking at existing documentation, talking to customers, discussion of features, etc.
  • Requirements specification - Formal list of realistic requirements
  • Requirements validation - Give the specification to the customer

Requirements Engineering Stages

Plan driven methodologies

  • All process activities planned in advance
  • Progress measured against plan
  • Do not deviate from plan

Waterfall Model

  • Strict linear ordering of processes - one must be complete before the next begins
  • Failure on any step means restarting
Good forBad for
No changes in requirements expectedChanging requirements
Any sized team, any locationsCustomer to see results quickly
Componentising sections of the system

Waterfall Model

Incremental Development

  • In stages, customer feedback between iterations
  • Specification, development and validation can take place concurrently
  • Each step is still planned in full, and tested against it’s specification
Good forBad for
Reducing cost of changing requirementsEstimating development costs
Customer interacting with development cycleMaintaining consistency with new features
Componentising sections of the systemCosts - expensive to redocument and redevelop

Incremental Development


  • Uses common off-the-shelf systems (COTS), or large company libraries
  • Typically good for webapps, frameworks etc.
  • Development can be rapid and less costly
  • Less testing needed on pre-implemented features

Reuse-oriented Software Engineering

Agile methodologies

  • Specification, design and implementation interleaved
  • Stakeholders give feedback at every stage
  • Manifesto: Customer involvement, Incremental delivery, People not process, Embracing change, Maintain simplicity
  • Less focus on documentation, needs heavy customer involvement and small, experienced teams
  • Can produce prototypes & Minimum Viable Products

All agile methodologies share these disadvantages.

Extreme Programming (XP)

  • Everything super fast: Incrementl delivery, fast iterations, automated builds and tests, continual code refactoring
  • Customer builds every ~2 weeks
  • Implement smallest possible change to create feature for atomic functionality
  • Design for feature done just before implementing that feature
  • Test-driven development: Write test before implementing
  • Collective ownership: ≥2 people responsible for any section of code

Extreme Programming cycles


  • 3 stages: Outline planning, Sprint cycles, Project closure
  • Sprints: ~2-4 weeks, daily meetings, items completed from backlog
  • Scrum master: interfaces between dev team and customer
  • Good if you want to manage a project in chunks, have unstable requirements and want smaller release cycles

Scrum Methodology Stages

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