E-R Model and Normalization…………

When we carefully define an E-R diagram, identifying all entities correctly, the tables

generated from the E-R diagram should not need further normalization. However,

there can be functional dependencies between attributes of an entity. For instance,

suppose an employee entity had attributes department-number and department-address,

and there is a functional dependency department-number department-address. We

would then need to normalize the relation generated from employee.

Most examples of such dependencies arise out of poor E-R diagram design. In the

above example, if we did the E-R diagram correctly, we would have created a department

entity with attribute department-address and a relationship between employee and

department. Similarly, a relationship involving more than two entities may not be in a

desirable normal form. Since most relationships are binary, such cases are relatively

rare. (In fact, some E-R diagram variants actually make it difficult or impossible to

specify nonbinary relations.)

Functional dependencies can help us detect poor E-R design. If the generated relations

are not in desired normal form, the problem can be fixed in the E-R diagram.

That is, normalization can be done formally as part of data modeling. Alternatively,

normalization can be left to the designer’s intuition during E-R modeling, and can be

done formally on the relations generated from the E-R model.



About Dinesh

I am engineering student........ I am selected in Microsoft Student Partner as MSP............

Posted on February 3, 2011, in Knowledge. Bookmark the permalink. 4 Comments.

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