A Stratification of Class Family Dependencies

Instances of a group of classes used together generally only work correctly if each object interacts with other objects that satisfy certain constraints. For example, a Node in a graph might expect to be attached to an Edge, and similarly for ColorNode and ColorEdge. This paper analyzes a series of progressively richer constraints that such objects may place on each other, thereby establishing a stratification of several kinds of dependencies in class families. We examine the constraint specification mechanisms available with traditional object-oriented polymorphism, F-bounded parametric polymorphism, and virtual attributes, and explain the trade-offs.