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It is possible to define a set of entities and the relationships among
them in a number of different ways.
The main difference is in how we deal with attributes.
The question of what constitutes an entity and what constitutes an
attribute depends mainly on the structure of the real world situation
being modeled, and the semantics associated with the attribute in
- Consider the entity set employee with attributes
employee-name and phone-number.
- We could argue that the phone be treated as an entity itself,
with attributes phone-number and location.
- Then we have two entity sets, and the relationship set EmpPhn
defining the association between employees and their phones.
- This new definition allows employees to have several (or zero) phones.
- New definition may more accurately reflect the real world.
- We cannot extend this argument easily to making employee-name
Page created and maintained by Osmar R. Zaï ane
Sun Sep 10 17:02:35 PDT 1995