Waterfall model/Linear Sequential Model/classic life cycle

Since the time it was first published by Winston W. Royce in 1970, the waterfall model has been used widely in the field of software development

Waterfall model phases:

• Requirements analysis and definition

• System and software design

• Implementation and unit testing

• Integration and system testing

• Operation and maintenance

The main drawback of the waterfall model is the difficulty of accommodating change after the process is underway. One phase has to be complete before moving onto the next phase.

• Each phase terminates only when the documents are complete and approved by the SQA group.

• Implementation and unit testing

• Integration and system testing

• Operation and maintenance

• Maintenance begins when the client reports an error after having accepted the product. It could also begin due to a change in requirements after the client has accepted the product 

 Waterfall model: Advantages:

• Disciplined approach

• Careful checking by the Software Quality Assurance Group at the end of each phase.

• Testing in each phase.

• Documentation available at the end of each phase.

Waterfall model problems:

• It is difficult to respond to changing customer requirements.

• Therefore, this model is only appropriate when the requirements are well-understood and changes will be fairly limited during the design process.

• Few business systems have stable requirements.

• The waterfall model is mostly used for large systems engineering projects where a system is developed at several sites.

• The customer must have patience. A working version of the program will not be available until late in the project time-span

• Feedback from one phase to another might be too late and hence expensive.