<P> The advantages of RAD include: </P> <Ul> <Li> Better quality . By having users interact with evolving prototypes the business functionality from a RAD project can often be much higher than that achieved via a waterfall model . The software can be more usable and has a better chance to focus on business problems that are critical to end users rather than technical problems of interest to developers . </Li> <Li> Risk control . Although much of the literature on RAD focuses on speed and user involvement a critical feature of RAD done correctly is risk mitigation . It's worth remembering that Boehm initially characterized the spiral model as a risk based approach . A RAD approach can focus in early on the key risk factors and adjust to them based on empirical evidence collected in the early part of the process . E.g., the complexity of prototyping some of the most complex parts of the system . </Li> <Li> More projects completed on time and within budget . By focusing on the development of incremental units the chances for catastrophic failures that have dogged large waterfall projects is reduced . In the Waterfall model it was common to come to a realization after six months or more of analysis and development that required a radical rethinking of the entire system . With RAD this kind of information can be discovered and acted upon earlier in the process . </Li> </Ul> <Li> Better quality . By having users interact with evolving prototypes the business functionality from a RAD project can often be much higher than that achieved via a waterfall model . The software can be more usable and has a better chance to focus on business problems that are critical to end users rather than technical problems of interest to developers . </Li> <Li> Risk control . Although much of the literature on RAD focuses on speed and user involvement a critical feature of RAD done correctly is risk mitigation . It's worth remembering that Boehm initially characterized the spiral model as a risk based approach . A RAD approach can focus in early on the key risk factors and adjust to them based on empirical evidence collected in the early part of the process . E.g., the complexity of prototyping some of the most complex parts of the system . </Li>

Briefly describe the four phases of the rapid application development (rad) model