Modules vs. Sub-systems
Sub-system
- Is a system in its own right whose operation does not depend on the services provided by other sub-systems
- Are composed of modules
- Have defined interfaces which are used for communication with other sub-systems
Module
- Is a system component that provides one or more services to other modules
- It is not normally considered to be an independent system
Both
- Encapsulate the representation of an abstraction
- Hide a design decision, unnecessary details, a secret, implemention