First of all, the waterfall model was the first process model to be introduced. It is very simple to use. In this model, each phase must be completed before the next phase can begin. There is no overlap in phases. This is the first SDLC approach used for software development. One of the advantages of using the waterfall model is that it is simple and easy to understand and use. Since one phase is carried out at the same time, it is easy to maintain. The phases are processed and completed one by one and they do not overlap. The waterfall model works well for small projects where the requirements are very well understood. The results are very well documented. One of the disadvantages of the waterfall model is that it cannot adopt changing requirements. It is very difficult to return to another phase. For example, at a certain step, you have to go back to a previous step. This would be very difficult to do. This also doesn't work for long, ongoing projects. Say no to plagiarism. Get a tailor-made essay on “Why Violent Video Games Should Not Be Banned”? Get the original essay Second, the agile model. The Agile SDLC model is a combination of iterative and incremental process models focused on process adaptability and customer satisfaction through rapid delivery of a working software product. Agile methods divide the product into small, incremental releases. These versions are provided in iterations. Each iteration typically lasts around one to three weeks. Each iteration involves cross-functional teams working on different areas simultaneously. The advantage of an Agile model is that it is a very realistic approach to software development. Little to no planning is required and it is easy to manage. It provides early partial working solutions. And this gives flexibility to developers. Some disadvantages of the Agile model are that it is not suitable for managing complex dependencies. There is more risk of durability, maintainability and scalability. There is very high individual dependency, as the documentation generated is minimal. Additionally, technology transfer to new team members can 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 are integrated to create a complete product enabling faster product delivery. The customer gains early visibility into the software and can provide feedback on design, delivery and other requirements. Some advantages of the RAD model are that it reduces development time since all prototypes are developed in parallel. This increases component reuse and allows for rapid initial examinations. This encourages customer feedback as it benefits from early visibility. And this increases the reuse of components. Some disadvantages of this model are that it depends on a strong team and individual performance to identify business needs. This requires highly skilled developers and designers. It cannot be used for cheaper projects because the cost of modeling and automated code generation can be very high..