Capture shared attributes of objects that represent an abstract identity or "sameness" and support the creation of new abstractions without writing code.

Participants

• Abstraction - instances of this class represent abstractions: groupings of things that are abstractly the same.
• Occurrence - instances of this class represent things that can be grouped into abstractions.

The occurrences can be just about anything. The abstractions often arise in one of the following situations:

• you have multiple copies of the "same" thing: books, video recordings, audio recordings.
• you have multiple schedulings of the "same" event: courses, flights, television shows.

• Failure to model the abstraction results in duplication of shared attributes. This increases the possibility of errors and inconsistencies.
• Using inheritance to capture the shared attributes means that you must create a new class to create a new abstraction. Classes are created statically. Objects can be created dynamically.