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.