Extended ER Diagrams
When an RDB implements an Extended ERD (EERD), a tupleís fkeys or inter-object cross-references can identify either a super-class object or an associated parent or container object (instance of a class).
- Both types of fkeys share the same integer key value range, although they have distinct semantic meaning.
To improve readability, EERDís should use different styles for inheritance than for instance-level associations
inherits from AA and is a