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Rule 8
If in rule 1 you find subclasses then transform them according to this rule.
Definition rule 8
Define a relational scheme R for the superclass C with the
attributes A(R)=(K, A1, A2, .., An), where K is the primary key. For each
subclass create a new relational scheme Ri with their attributes and the
primary key K of superclass C as an additional attribute. The primary key of Si
is also K.
In this example you can see the application
of rule 8:
Using the superclass define a relational scheme R with a
primary key K:
Employee(ENumber)
For each subclass create a relational scheme:
Technician
Engineer(Training)
Add the primary key K of the superclass as attribute of the
subclasses and use it also as primary key:
Employee(ENumber),
Technician(ENumber),
Engineer(ENumber, Training)
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