An entity type can inherit attributes and relationship types
from any number of supertypes. The
isa element specifies a supertype of an
When you specify that A is a B ERW keeps in sync the tables reifying the two types (i.e., for each entity in A there is a corresponding entity with the same id in B). Whenever you edit an entity of type A, independently of whether you are editing it in the context of A or B, ERW knows that it is of type A and acts accordingly.