An arrangement of classes in a taxonomic (subclass-superclass) hierarchy. A class hierarchy represents an 'is-a' relation, where a class X is a subclass of A if every instance of X is also an instance of A. A class hierarchy thus represents a set of classes related by inheritance. A class hierarchy is typically shown as a tree structure for single inheritance or as a lattice structure for multiple inheritance (where nodes represent classes and are connected by arcs to indicate inheritance relations).