The sequential phases in Waterfall model are: -
Requirement Gathering and analysis: All possible requirements of the system to
be developed are captured in this phase and documented in a requirement
System Design: The requirement specifications from first phase are studied in this
phase and system design is prepared. System Design helps in specifying hardware
and system requirements and also helps in defining overall system architecture.
Implementation: With inputs from system design, the system is first developed in
small programs called units, which are integrated in the next phase. Each unit is
developed and tested for its functionality which is referred to as Unit Testing.
Integration and Testing: All the units developed in the implementation phase are
integrated into a system after testing of each unit. Post integration the entire system
is tested for any faults and failures.
Deployment of system: Once the functional and nonfunctional testing is done, the
product is deployed in the customer environment or released into the market.
Maintenance: There are some issues which come up in the client environment. To
fix those issues patches are released. Also, to enhance the product some better
versions are released. Maintenance is done to deliver these changes in the customer
All these phases are cascaded to each other in which progress is seen as flowing
steadily downwards (like a waterfall) through the phases. The next phase is started
only after the defined set of goals are achieved for previous phase and it is signed
off, so the name "Waterfall Model". In this model phases do not overlap.
2.2.2 Waterfall Model Application
Every software developed is different and requires a suitable SDLC approach to be
followed based on the internal and external factors. Some situations where the use
of Waterfall model is most appropriate are: