The BDD is the primary kind of diagram you create to communicate structural information about a system. A BDD enables you to express the types of structures that can exist internally within a system and externally in a system’s environment. You can also use BDDs to express the types of services each structure provides and requires, the types of constraints each structure must conform to, and the types of values that can exist within an operational system.
Generalization relationships between elements let you define type hierarchies and design to abstractions. This is a powerful design technique—one that creates extensibility in your system design by decoupling the clients of services from any specific implementation of a provider of those services. As your stakeholders’ requirements evolve over time, you can modify existing providers or add new ones with minimal impact on the rest of the system design.