But any extraction of the attribute must specify not only the proper name, but the name of the type in which the desired attribute is defined. How attributes differ from methods See this list . They have some degree of independence from each other. The values of these attributes are completely dependent on the basic attributes and methods. The semantics for derived attributes should explain how to obtain the derived attribute from the basic attributed.
Derived attributes can be useful.
An agent that does not know how to directly extract a derived attribute can figure it out in terms of the basic attributes. Also, derived attributes can be added to a type description without changing its basic definition.