Extended Entity Relationship DIagram

A supertype is a general entity type that can be subdivided into specialized subtypes.

A subtype is a general entity type that can be subdivided into specialized supertypes.

A supertype and subtype are always identical in attributes.

A subtype contains all attributes of all supertypes.

Identifier and common attributes

Unique attributes for each subtype

Only relationship attributes

No attributes are shared

PersonID

EmployeeID

CustomerID

SupplierID

Hourly_Rate

Employee_number

Annual_Salary

Stock_Option

Contract_Number and Billing_Rate

Employee_Number and Address

Hourly_Rate and Annual_Salary

Stock_Option and Date_Hired

CAR

TRUCK

MOTORCYCLE

VEHICLE

EmployeeID

PersonID

LoyaltyPoints

ProductSupplied

Total specialization rule

Partial specialization rule

Referential integrity rule

Entity integrity rule

To ensure every instance of a supertype is a member of at least one subtype

To define the attributes of a supertype

To create relationships between different entities

To enforce data integrity in all tables

Total Specialization Rule

Partial Specialization Rule

Disjoint Rule

Overlap Rule

Disjointness constraints determine if an instance of a supertype can be a member of multiple subtypes simultaneously.

Disjointness constraints only apply to partial specialization.

Disjointness constraints are not relevant in ER diagrams.

Disjointness constraints have two possible rules: disjoint rule and overlap rule.

Fundamentals of Database Systems by Elmasri & Navathe (7th Edition)

Database System Concepts by Silberschatz, Korth & Sudarshan (6th Edition)

Modern Database Management by Hoffer, Ramesh & Topi (12th Edition)

Database System Design: Design, Implementation and Management by Coronel & Morris (12th Edition)