Referential Integrity
Constraints on
associations should be examined for referential integrity implications in the
database models. Ask when referential integrity rules should be enforced.
Immediately, or at a later time? When you are modeling object instances over
time, you may need to introduce extra object classes to capture situations
where attribute values can change over time. For instance, if you need to keep
an audit trail of all changes to an order or invoice, you could add a date and
time attribute to the order or invoice objects to allow for storage of a
historical record of their instances. Each change to an instance would result
in another instance of the object, stamped for data and time of instance
creation.
Insert Rules
These rules determine the
conditions under which a dependent class may be inserted and they deal with
restrictions that the parent classes impose upon such insertions. The rules can
be classified into six types.
Dependent
: Permit insertion of child
class instance only when the matching parent class instance already exists
Automatic : Always
permit insertion of a child class instance. If the parent class instance does
not exist, create one
Nullify : Always
permit insertion of the child class instance.
Default : Always
permit insertion of a child class in séance.
Customized : Allow child
class instance insertion only if certain validity constraints are met.
No Effect : Always
permit insertion of the child class instance. No matching parent class
instances may or may not exist. No validity checking is performed.
Domain
integrity
These integrity rules
define constraints on valid values that attributes can assume. A domain is a
set of valid values for a given attribute, a set of logical of conceptual
values from which one or more attributes can draw their values. For example,
India state codes might constitute the domain of attributes for employee state
codes, customer state codes, and supplier state codes. Domain characteristics
include such things as:
•
Data type
• Data length
• Allowable value ranges
• Value uniqueness
• Whether a value can be null, or not.
Domain describes a valid set of values for an attribute, so that
domain definitions can help you determine whether certain data manipulation
operations make sense.
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