In the top-down model, the system is first viewed as a generalized structure and is then decomposed into more specific components, whereas in the bottom-up model, the system is first viewed as a series of specific and basic components and then continues to be composed to reach a higher level of abstraction. Top-down design is a model in which the designer starts with the high-level requirements and works their way down to the lowest level of detail. It is the most common approach for systems analysis and design, as it allows for each layer to be built upon the previous layer, and it allows for communication between team members. Bottom-up design is a model in which the designer starts with low-level details, such as how data is stored or how users will interact with a system, and works their way up to higher levels of abstraction. This approach is more common in software development than systems analysis but can still be used when working on large systems.