One key abstraction

A class should capture one and only one key abstraction. --Riel's Heuristic 2.8, Arthur Riel 1996

A class should represent one key abstraction of the domain model, no more and no less. A key abstraction is generally a noun in a requirements statement. If a key abstraction maps to more than one class, the designer may be representing each function of the abstraction as a class. If several key abstractions map to one class, the designer may be creating a centralized system and needs to split the class into several smaller classes.

See also

• Split large classes
• God object
• Riel's heuristics
• Single responsibility principle
• Separation of concerns
• Interface segregation principle
• Extract Class
• Divergent change smell