Databases Reference
In-Depth Information
DATA INTEGRITYAND QUALITY
RENTAL_PACKAGE
PK
FK->VEHICLE_TYPE.Veh TypeName
PackageID#
Rate
VehTypeName
VEHICLE
FK->VEHICLE_TYPE.Veh TypeName
PK
VehlD#
Make
VehTypeName
VEHICLE_TYPE
PK
VehTypeName
Exhibit 28-2. A relational model generated from the E-R model in Exhibit 11-1.
Attribute referential integrity ensures that a value appearing in the ref-
erencing attribute of one relation appears in the referenced attribute of the
other relation, where these two relations are not necessarily distinct, and
referencing or referenced attributes can be a combination of multiple at-
tributes. The following section provides the formal definition.
The Formal Definition of Attribute Referential Integrity
r1 (R1) and r2 (R2) are relations of a schema R1 and R2, respectively. A
subset
α
of R1 is a referencing attribute referring to a referenced attribute
β
in relation r2 if it is required that for every tuple t1 in r1, there must be a tu-
ple t2 in r2 such that t1[
α
] = t2[
β
]. Requirements of this form are called the
attribute referential integrity constraint.
This can be written as
∏
α
(r1)
∏
α
α
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