SDLC - WaterFall, Spiral, Agile and Test Life Cycle

Waterfall Model:

The waterfall model is a popular version of the systems development life cycle model for software engineering. Often considered the classic approach to the systems development life cycle, the waterfall model describes a development method that is linear and sequential. Waterfall development has distinct goals for each phase of development. Imagine a waterfall on the cliff of a steep mountain. Once the water has flowed over the edge of the cliff and has begun its journey down the side of the mountain, it cannot turn back. It is the same with waterfall development. Once a phase of development is completed, the development proceeds to the next phase and there is no turning back.

The advantage of waterfall development is that it allows for departmentalization and managerial control. A schedule can be set with deadlines for each stage of development and a product can proceed through the development process like a car in a carwash, and theoretically, be delivered on time.

The disadvantage of waterfall development is that it does not allow for much reflection or revision. Once an application is in the testing stage, it is very difficult to go back and change something that was not well-thought out in the concept stage.

The model is also called Classic or Linear Sequential model. A linear and orderly sequence of steps from System Study to Implementation. When one phase ends, then the next phase begins. Appropriate if system’s requirements are stable and well understood.


  • Building a well-defined maintenance releases of a product.
  • Porting an existing application to a new platform.

    Biggest Risks

  • Customer gets to see it only in the end.
  • Correctness and completeness of earlier phases is a prerequisite of each phase.

    Stages: Project Planning -> Requirements definition -> Design -> Development -> Integration and Testing -> Installation/Acceptance -> Maintenance


Spiral Model:

  1. Based on risks such as: Poor requirements understanding, architecture definition, performance, technologies etc.
  2. Riskier one first.
  3. Each mini-project could be in a non-risk based model such as waterfall.
    • Identify objectives, alternatives, constraints
    • Identify and resolve risks. Choose the right alternative.
    • Develop for that iteration. Verify it.
    • Plan for the next iteration.
  4. Appropriate when the challenges are huge and many.
  • There are four phases in the "Spiral Model" which are: Planning, Evaluation, Risk Analysis and Engineering. These four phases are iteratively followed one after other in order to eliminate all the problems, which were faced in "The Waterfall Model". Iterating the phases helps in understating the problems associated with a phase and dealing with those problems when the same phase is repeated next time, planning and developing strategies to be followed while iterating through the phases.

    In Spiral model it splits the project to multiple mini-projects;


Agile Process:

Agile aims to reduce risk by breaking projects into small, time-limited modules or timeboxes ("iterations") with each iteration being approached like a small, self-contained mini-project, each lasting only a few weeks. Each iteration has it own self-contained stages of analysis, design, production, testing and documentation. In theory, a new software release could be done at the end of each iteration, but in practice the progress made in one iteration may not be worth a release and it will be carried over and incorporated into the next iteration. The project's priorities, direction and progress are re-evaluated at the end of each iteration.


Test life cycle:

1. Test Requirements stage - Requirement Specification documents, Functional Specification documents, Design Specification documents (use cases, etc), Use case Documents, Test Trace-ability Matrix for identifying Test Coverage.
2. Test Plan - Test Scope, Test Environment, Different Test phase and Test Methodologies, Manual and Automation Testing, Defect Management, Configuration Management, Risk Management, Evaluation & identification – Test, Defect tracking tools, test schedule, resource allocation.
3. Test Design - Traceability Matrix and Test coverage, Test Scenarios Identification & Test Case preparation, Test data and Test scripts preparation, Test case reviews and Approval, Base lining under Configuration Management.
4. Test Environment Setup - Test Bed installation and configuration, Network connectivity's, All the Software/ tools Installation and configuration, Coordination with Vendors and others.
5. Test Automation - Automation requirement identification, Tool Evaluation and Identification, Designing or identifying Framework and scripting, Script Integration, Review and Approval, Base lining under Configuration Management.
6. Test Execution and Defect Tracking - Executing Test cases, Testing Test Scripts, Capture, review and analyze Test Results, Raise the defects and tracking for its closure.
7. Test Reports and Acceptance - Test summary reports, Test Metrics and process Improvements made, Build release, Receiving acceptance.