Database Reference
In-Depth Information
then briefly revisited
multivalued fields
,
and you learned how to use a proper one-to-many
relationship to resolve a multivalued field more efficiently. Next, we discussed self-refer-
encing relationships, and you now know that you establish them in a very similar manner
todual-tablerelationships.Youthenlearnedthatyoumustreviewallofthetablestructures
and ensure that they still conform to the Elements of the Ideal Table.
Foreignkeyswerethenexttopicofdiscussion,andyoulearnedthateveryforeignkeymust
comply with the Elements of a Foreign Key. You now know that it can be very important
for a foreign key to share the same name as its parent primary key, that you must modify
certain elements of a field specification for a field that serves as a foreign key, and that a
foreign key must draw its values from the parent primary key.
We then discussed relationship characteristics. You learned how to define a
deletion rule
for a relationship and that there are four ways you can define it. Next, you learned how
to identify the
type of participation
and
degree of participation
for each table within a
dual-tablerelationshipandforeachkeyfieldinaself-referencingrelationship.Asyounow
know,youcandesignatethetypeofparticipationas
Mandatory
or
Optional.
Youalsoknow
that the degree of participation gauges the minimum and maximum number of interrelated
records that can exist within a given relationship. Finally, you learned that you must verify
therelationshipswithusersandmanagementandthatyoucanuseachecklisttoaccomplish
this task.
The chapter closed with a look at
relationship-level integrity.
You learned that a relation-
ship attains this type of integrity after you've verified that it is properly established and its
characteristics are suitably set.
Review Questions
ship.
the database?
tionships?
