The General Model-Software life cycle models describe phases of the software cycle and the order in which those phases are executed. There are tons of models, and many companies adopt their own, but all have very similar patterns. Each phase produces deliverables required by the next phase in the life cycle.
Requirements- This phase is the main focus of the project managers and stake holders.
Design-The software system design is produced from the results of the requirements phase.
Implementation-Code is produced from the deliverables of the design phase during implementation, and this is the longest phase of the software development life cycle.
Testing-During testing, the implementation is tested against the requirements to make sure that the product is actually solving the needs addressed and gathered during the requirements phase. (CIO.2002).
Waterfall Model-This is the most common and classic of life cycle models, also referred to as a linear-sequential life cycle model. It is very simple to understand and use. In a waterfall model, each phase must be completed in its entirety before the next phase can begin. At the end of each phase, a review takes place to determine if the project is on the right path and whether or not to continue or discard the project. Unlike what I mentioned in the general model, phases do not overlap in a waterfall model. (DOJ,2003).
Advantages- Simple and easy to use. Easy to manage due to the rigidity of the model – each phase has specific deliverables and a review process. Phases are processed and completed one at a time. Works well for smaller projects where requirements are very well understood. Disadvantages - Adjusting scope during the life cycle can kill a project. No working software is produced until late during the life cycle. High amounts of risk and uncertainty. Poor model for complex and object-oriented projects.