Views

Specialization

An entity set E that is a specialization of one parent entity set and satisfies:

1. Only typing Attributes declared
2. No foreign key constraints reference E
3. All entity sets that are specializations of E are mapped to views

Need to add a new two-valued typing attribute is-E

• Combine with E’s existing typing attributes to the parent entity set to enable a view definition for the mapping of E

Generalization

Generalization entity set E of two or more child entity sets

• No foreign key constraints that reference E
• All attributes on E are defined on each child entity set to enable a view definition for the mapping of E

create view Vehicle as (
	( select LicenseNum, MakeAndModel, Price from Truck )
	union
	( select LicenseNum, MakeAndModel, Price from Car )
)