Generally, there is one design model of the system; analysis produces a rough sketch of the system, which is refined further in design. The upper layers of this model describe the application-specific, or more analysis-oriented, aspects of the system. Using a single model reduces the number of artifacts that must be maintained in a consistent state.
In some companies ”those in which systems live for decades or there are many variants of the system ”a separate analysis model has proved useful. The analysis model is an abstraction, or generalization, of the design. It omits most of the details of how the system works and provides an overview of the system's functionality. The extra work required to ensure that the analysis and design models remain consistent must be balanced against the benefit of having a view of the system that represents only the most important details of how the system works.