Extended ER Diagrams

When an RDB implements an Extended ERD (EERD), a tuple’s 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, EERD’s should use different styles for inheritance than for instance-level associations

0..*

In this example, CC both

inherits from AA and is a

component of the

composite entity BB.

It contains two fkeys,

(say) AAid and BBid.

When an RDB implements an Extended ERD (EERD), a tuple’s fkeys or inter-object cross-references can identify either a super-class object or an associated parent or container object (instance of a class).