Waterfall Model

The Waterfall Model

• It is an example of plan-driven process.

  graph LR
    rd[Requirement Definition]
    sasd[System and Software Design]
    iaut[Implementation and Unit Testing]
    iast[Integration and System Testing]
    oam[Operation and Maintenance]

    rd-->sasd-->iaut-->iast-->oam

    oam-->iast
    oam-->iaut
    oam-->sasd
    oam-->rd

Phases

• Requirements Analysis and Definition
  • Establish services, constraints, and goals by consultation with system users.
  • Defined in detail.
  • Serve as a system specification.
• System and Software Design
  • Allocate the requirements to either hardware or software system by establishing an overall system architecture.
  • Identifying and describing the fundamental software system abstractions and their relationships.
• Implementation and Unit Testing
  • Software design is realized as a set of programs of program units.
  • Unit testing involves verifying that each unit meets its specification.
• Integration and System Testing
  • The individual program units or programs are integrated and tested as a complete system.
  • After testing, the software system is delivered to the customer.
• Operation and Maintenance
  • The system is installed and put into practical use.
  • Maintenance involves correcting errors which were not discovered in earlier stages.

Problems

• It is difficult to make any change during the development process. In principle, a phase has to be done before moving onto the next phase.
• Inflexible partitioning of the project into distinct stages makes it difficult to respond to changing customer requirements.
• The waterfall model is mostly used for large system engineering projects, where a system is developed at several sites.