The spiral model combines some ideas of the iterative model but also the rigid characteristics of the waterfall model. The spiral model has four phases: Identification, Design, Construction and Evaluation. A spiral project goes through these phases in iterations, then the cycle repeats until the final result is produced. The application is released incrementally. The spiral model is applied when: Say no to plagiarism. Get a tailor-made essay on "Why Violent Video Games Shouldn't Be Banned"? Receive an original essay When the budget is low and risks need to be assessed The project presents a medium to high risk. The customer is unsure of their needs. The requirements are complex and need evaluation to achieve clarity. Significant changes to the product are expected during the development cycle. Advantages of the spiral model: Requirements can be changed. Promotes the use of prototypes. Requirements can be defined more accurately. Users can see the system in the early stages of development. Development can be divided into modules and difficult modules can be developed first. Disadvantages of the model: The end of the project may not be known in advance. Management is more complex. The spiral can go on indefinitely. Not suitable for small or low risk projectsThe waterfall model is a methodology based on a sequential design process. The waterfall model flows from one phase to another, and phases cannot be revisited once completed. You must finish one phase to start the next phase. The waterfall model consists of 6 phases, namely: requirements analysis, design, implementation, testing, launch and maintenance. The waterfall model is used for small projects that have clear requirements from the beginning. Applications of the waterfall model: It can be easily used for small projects. The requirements are well defined, clearly documented and fixed. The product implementation is stable. The technology does not change and is well managed by the project team. Staff does not require special training for this template.Advantages of this template:Simple and easy to understand and useEasy to handle due to the high rigidity of the template.The phases flow from one to another.Works well for smaller projects where the requirements they are very well included.Clearly defined steps.Process and results are well documented. Disadvantages of the model: high risk and uncertainty. Not suitable for complex and long-term projects. Not suitable for projects where requirements pose a moderate to high risk of change. Once an application is tested, it is difficult to change the functionality. No working software is produced until end of life. Agile methodologies are in the 2001 agile manifesto, these include: Scrum, Lean, XP, Crystal, FDD and DSDM. Agile projects are flexible and contain iterative design and construction processes. Agile models are similar to the iterative model, as both models work through iterations. The model uses an adaptive approach, which allows changes to be made, unlike more rigid models such as Waterfall or V-model, where a predictive approach with clear requirements is used. Agile development is a set of principles and values ​​for developing a project. The four principles of agile methods are: individuals and interactions, delivering working software, collaborating with customers, and responding to change. The advantages of this model are:The model provides a very realistic approach to develop the product.It promotes teamwork and cross-training.The functionality can be developed quickly.The requirements.