First of all, the waterfall model was the first process model to be introduced. It is very easy to use. In this model, each phase must be completed before the next phase can begin. There is no overlap in the phases. It is the first SDLC approach used for software development. Some advantages of using the waterfall model are that it is simple and easy to understand and use. Since it is done one step at a time, it is easy to maintain. Phases are processed and completed one at a time and do not overlap. The waterfall model works well for smaller projects where the requirements are well understood. The results are very well documented. Some disadvantages of the waterfall model are that it cannot adopt changes in requirements. It is very difficult to go back to another phase. For example, during a certain phase it is necessary to return to the previous phase. It would be very difficult to do so. It also doesn't work for long, ongoing projects. Say no to plagiarism. Get a tailor-made essay on "Why Violent Video Games Shouldn't Be Banned"? Get an original essay Second, the agile model. The Agile SDLC model is a combination of iterative and incremental process models with a focus on process adaptability and customer satisfaction through rapid delivery of the working software product. Agile methods break the product into small incremental builds. These builds are delivered in iterations. Each iteration typically lasts about one to three weeks. Each iteration involves cross-functional teams working simultaneously on various areas. The advantage of an Agile model is that it represents a very realistic approach to software development. Little to no planning is required and it is easy to manage. Provides initial partial operational solutions. And it offers flexibility to developers. Some disadvantages of the Agile model are that it is not suitable for managing complex dependencies. There is more risk of sustainability, maintainability and extensibility. There is a very high individual dependency, as minimal documentation is generated. Additionally, transferring technology to new team members may be difficult due to lack of documentation. Third, the RAD model. Rapid Application Development (RAD) is a software development method that uses minimal planning in favor of rapid prototyping. Functional modules are developed simultaneously as prototypes and integrated to realize the complete product for faster delivery. The customer gets early visibility into the software and can provide feedback on design, delivery and other requirements. Some advantages of the RAD model are the reduction of development time since all prototypes are developed in parallel. Reusability of components increases and rapid initial revisions occur. Encourage customer feedback as the customer gets early visibility. And it increases the reusability of the components. Some disadvantages of this model are that it depends on a strong team and individual performance to identify business requirements. It requires highly skilled developers and designers. It cannot be used for cheaper projects as the cost of modeling and automated code generation could be very high.