Referential Integrity for Database Design - High-Performance Web Databases: Design, Development, and Deployment - page 428

is included instead of separately creating an entity type as in

Exhibit 1. On the lines emanating from the RI rectangle, a referenced at-
tribute (

_

VEHICLE TYPE

_ . VehTypeName ), and a referencing attribute (

RENTAL PACKAGE VEHI-

), are specified explicitly; whereas, in Exhibit 11-1 this
referential integrity is implicitly represented via the foreign key concept.

. VehTypeName CLE

The Relational Model

The ARI constraint can be directly represented on the referencing at-
tribute of a relation by specifying a referenced attribute of the other rela-
tion. A notation representing this is:

ARI(<referencing attribute>) → <referenced attribute>

For example, Exhibit 5 shows a set of relations generated from the E-R
model shown in Exhibit 4 . By specifying the attribute referential integrity
constraint directly on . VehTypeName , there is no need to create a new VEHICLE

relation of because no foreign keys are involved to specify the

referential integrity constraints as in Exhibit 2. Instead, the referential integ-
rity constraint on

_

VEHICLE TYPE

VehTypeName can be directly and explicitly specified on

the referencing attribute, . VehTypeName , referring to the referenced

VEHICLE

attribute, _ . VehTypeName . RENTAL PACKAGE

RENTAL_PACKAGE

PK

TermID# Rate VehTypeName

VEHICLE

ARI->RENTAL_PACKAGE.VehTypeName

PK

VehlD# Make VehTypeName

Exhibit 28-5. A relational model generated from the E-R model in Exhibit 11.4.