Notation for Inheritance
An inheritance relation is indicated on a data structure diagram by a T-shaped branch structure from the superclass type to each subclass type (with no arrow heads or tails).
Bde supports this EERA extension of ERA diagrams. The cross-bar is a special node type, identified by its height-to-width ratio.
(this implies a mutually exclusive relationship,
not a 1:M parent-child relation, among instances.)