The Design Model

The design model builds on the analysis model by describing, in greater detail, the structure of the system and how the system will be implemented. Classes that were identified in the analysis model are refined to include the implementation constructs.

The design model is based on the analysis and architectural requirements of the system. It represents the application components and determines their appropriate placement and use within the overall architecture.

In the design model, packages contain the design elements of the system, such as design classes, interfaces, and design subsystems, that evolve from the analysis classes. Each package can contain any number of subpackages that further partition the contained design elements. These architectural layers form the basis for a second-level organization of the elements that describe the specifications and implementation details of the system.

Within each package, sequence diagrams illustrate how the objects in the classes interact, state machine diagrams to model the dynamic behavior in classes, component diagrams to describe the software architecture of the system, and deployment diagrams to describe the physical architecture of the system.

from here..