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attribute cascades to delete or update the matching values in the referenc-
ing attribute. Finally, the referencing attribute value is set to null or a default
value if a matching value in the referenced attribute is deleted or updated.
These three enforcement schemes are not, however, implemented in
current database management systems (DBMSs). The attribute referential
integrity constraint should be enforced by writing an application program
on the database or attaching a procedure (i.e., trigger) to a referenced or
referencing attribute.
SUMMARY
Specifying the attribute referential integrity has major advantages in da-
tabase systems design. An E-R and relational model for a problem domain
can be built compactly by dispensing with an entity type and a relation cre-
ated solely for specifying the referential integrity constraint of a foreign
key. Also, the referential integrity constraint of an attribute can be specified
directly and explicitly without using foreign keys.
Using the attribute referential integrity concept, a referential semantic
constraint can be explicitly represented in the E-R and relational models. In
the current DBMS environment, this new integrity constraint can be imple-
mented by writing an attached procedure on a referenced or referencing at-
tribute. In the future, CASE tools and DBMSs will be able to represent the
attribute referential integrity constraint.
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