Short note: Data dictionary stability

(Interpreted as the role of the data dictionary in OOAD and the stability of its contents.)

A data dictionary is a central repository that defines every data item used in the system: name, meaning, data type, size, allowed values, and the classes or processes that use it. In OOA it is the glossary of the domain model, listing each conceptual class, attribute and association with its definition.

Stability means the definitions in the dictionary stay consistent and change only in a controlled way.

• Domain concepts and their data (Customer, Account, Order) are comparatively stable, while functions and screens change often. Therefore an object model built on the data is more stable than a function-based model.
• Once an item is defined, every diagram and module must use the same name and meaning (consistency), so changes are made once in the dictionary and traced to every user of that item (change control and impact analysis).
• A stable dictionary avoids duplication, ambiguity and mismatch between analysts, designers and programmers.

Example entry:

A well maintained, stable data dictionary gives a common vocabulary and makes the system easier to maintain and extend.