Some Useful Module Structures

- Decomposition structure: The units are modules that are related to each other by the is-a submodule-of relation, showing how modules are decomposed into smaller modules recursively until the modules are small enough to be easily understood.

- Uses structure: In this important but overlooked structure, the units here are also modules, perhaps classes. The units are related by the uses relation, a specialized form of dependency.

- Layer structure: The modules in this structure are called layers. A layer is an abstract "virtual machine" that provides a cohesive set of services through a managed interface.

- Class (or generalization) structure: The module units in this structure are called classes. The relation is inherits from or is an instance of

- Data model: The data model describes the static information structure in tenns of data entities and their relationships.