Boyce\/Codd Normal Form<\/b>
———————-
It is just an extension to the third normal form. Third normal form ensures that non key attributes does not depend on any non key attribute but fully depend on the key[primary] attributes.<\/p>\n
Boyce codd normal form ensures that non key attributes are fully dependent on the total set of the primary key. Non-key attributes should not depend [only] on a subset of the key[primary] attributes.<\/p>\n
Fourth Normal Form:<\/b>
——————-
It tries to decompose an entity\/table into multiple entities\/tables when there are multiple independent[not dependent on each other] multivalued attributes in an entity\/table.<\/p>\n
For example: Consider a table with emp_number, skill name, objective of the employee. Employees may have many skills and also many objectives. Hence, skill_name, and objective are multivalued and also they do not depend on each other. This table will cause many redundant data.Better is to use two tables like:<\/p>\n
Emp_skill
Emp_num, Skill Name<\/p>\n
Emp_objective
Emp_num, Objective<\/p>\n
From: http:\/\/sitestree.com\/?p=4762
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Post Data:2012-01-14 02:58:00<\/p>\n
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