Waterfall Model -SDLC

The waterfall model is a sequential software development model in which development is seen as flowing steadily downwards (like a waterfall) through several phases.
Following phases are followed perfectly in sequential order:

    Requirements specification
    Design
    Implementation
    Integration
    Testing
    Installation
    Maintenance

When to use the waterfall model:

    Requirements are very well known, clear and fixed.
    Product definition is stable.
    There are no ambiguous requirements
    Ample resources with required expertise are available freely

Advantages of waterfall model:

    Due to the rigidity of the model it is easy to manage
    Phases are processed and completed one at a time.
    It is simple and easy to understand and use.
    Useful for smaller projects where requirements are very well understood.
    Each phase has specific deliverables and a review process.

 Disadvantages of waterfall model:

    In testing stage, it is very difficult to go back and change something that was not well-thought out in the   design stage.
    High amounts of risk and uncertainty.
    Not good model for complex and object-oriented projects.
    Poor model for ongoing projects.