LIS 558 - Normalization in the relational model

Normalization means splitting into simple relations (which correspond to Microsoft Access tables)
Normal form Rule Example of rule violation
First A relation cannot have repeating fields or groups. <author(1), author(2)..., title>
Second + every nonkey field must be functionally dependent on all of the key. <part, warehouse, quantity, warehouse-address> where the key is "part", "warehouse"
Third + a nonkey field cannot be functionally dependent on another nonkey field. <employee, department, department-location> where the key is "employee"
Fourth A relation cannot contain two or more independent multivalued attributes of an entity <employee, skill, language> where the key is "employee", "skill", "language"
Fifth Roughly, a relation cannot be reconstructed from several relations each having fewer fields and not all having the same key <salesperson, product, client> where it is known that, if a salesperson sells a product and sells to a client, then that salesperson sells that product to that client
In any relation, attribute A is functionally dependent on attribute B if, regardless of any insertions or deletions, the value of B determines the value of A; in other words, only one value of A occurs with a particular value of B.

Last updated July 5, 2001.
This page maintained by Prof. Tim Craven
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Faculty of Information and Media Studies
University of Western Ontario,
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