The waterfall model derives its name due to the cascading effect from one phase to the other as is illustrated in Figure1.1. In this model each phase well defined starting and ending point, with identifiable deliveries to the next phase.
Note that this model is sometimes referred to as the linear sequential model or the software life cycle.
The model consist of six distinct stages, namely:
1. In the requirements analysis phase
(a) The problem is specified along with the desired service objectives (goals)
(b) The constraints are identified
2. In the specification phase the system specification is produced from the detailed definitions of (a) and (b) above. This document should clearly define the product function.
Note that in some text, the requirements analysis and specifications phases are combined and represented as a single phase.
3.In the system and software design phase, the system specifications are translated into a software representation. The software engineer at this stage is concerned with:
a) Data structure
b) Software architecture
c) Algorithmic detail and
d) Interface representations
The hardware requirements are also determined at this stage along with a picture of the overall system architecture. By the end of this stage should the software engineer should be able to identify the relationship between the hardware, software and the associated interfaces. Any faults in the specification should ideally not be passed 'down stream'
4.In the implementation and testing phase stage the designs are translated into the software domain
a) Detailed documentation from the design phase can significantly reduce the coding effort.
b) Testing at this stage focuses on making sure that any errors are identified and that the software meets its required specification.
5.In the integration and system testing phase all the program units are integrated and tested to ensure that the complete system meets the software requirements. After this stage the software is delivered to the customer [Deliverable- The software product is delivered to the client for acceptance testing.]
6.The maintenance phase the usually the longest stage of the software. In this phase the software is updated to:
a) Meet the changing customer needs
b) Adapted to accommodate changes in the external environment
c) Correct errors and oversights previously undetected in the testing phases
d) Enhancing the efficiency of the software
Observe that feed back loops allow for corrections to be incorporated into the model. For example a problem/update in the design phase requires a 'revisit' to the specifications phase. When changes are made at any phase, the relevant documentation should be updated to reflect that change.
Advantages of Waterfall Model
a) Testing is inherent to every phase of the waterfall model
b) It is an enforced disciplined approach
c) It is documentation driven, that is, documentation is produced at every stage
Disadvantages of Waterfall Model
The waterfall model is the oldest and the most widely used paradigm. However, many projects rarely follow its sequential flow. This is due to the inherent problems associated with its rigid format.
a) It only incorporates iteration indirectly, thus changes may cause considerable confusion as the project progresses.
b) As The client usually only has a vague idea of exactly what is required from the software product, this WM has difficulty accommodating the natural uncertainty that exists at the beginning of the project.
c) The customer only sees a working version of the product after it has been coded. This may result in disaster any undetected problems are precipitated to this stage.