| Attributes |
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.
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
an entity.
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 question.
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