chapter 19 - normalization

chapter 19 - normalization - COP 4710 Database...

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Unformatted text preview: COP 4710: Database Systems (Chapter 19) Page 1 Mark Llewellyn COP 4710: Database Systems Fall 2009 Chapter 19 – Normalization COP 4710: Database Systems Fall 2009 Chapter 19 – Normalization School of Electrical Engineering and Computer Science University of Central Florida Instructor : Dr. Mark Llewellyn [email protected] HEC 236, 407-823-2790 http://www.cs.ucf.edu/courses/cop4710/fall2009 COP 4710: Database Systems (Chapter 19) Page 2 Mark Llewellyn • Normalization is a technique for producing a set of relations with desirable properties, given the data requirements of the enterprise being modeled. • The process of normalization was first developed by Codd in 1972. • Normalization is often performed as a series of tests on a relation to determine whether it satisfies or violates the requirements of a given normal form. • Codd initially defined three normal forms called first (1NF), second (2NF), and third (3NF). Boyce and Codd together introduced a stronger definition of 3NF called Boyce-Codd Normal Form (BCNF) in 1974. Normalization COP 4710: Database Systems (Chapter 19) Page 3 Mark Llewellyn • All four of these normal forms are based on functional dependencies among the attributes of a relation. • A functional dependency describes the relationship between attributes in a relation. – For example, if A and B are attributes or sets of attributes of relation R, B is functionally dependent on A (denoted A → B), if each value of A is associated with exactly one value of B. • In 1977 and 1979, a fourth (4NF) and fifth (5NF) normal form were introduced which go beyond BCNF. However, they deal with situations which are quite rare. Other higher normal forms have been subsequently introduced, but all of them are based on dependencies more involved than functional dependencies. Normalization (cont.) COP 4710: Database Systems (Chapter 19) Page 4 Mark Llewellyn • A relational schema consists of a number of attributes, and a relational database schema consists of a number of relations. • Attributes may grouped together to form a relational schema based largely on the common sense of the database designer, or by mapping the relational schema from an ER model. • Whatever approach is taken, a formal method is often required to help the database designer identify the optimal grouping of attributes for each relation in the database schema. • The process of normalization is a formal method that identifies relations based on their primary or candidate keys and the functional dependencies among their attributes. • Normalization supports database designers through a series of tests, which can be applied to individual relations so that a relational schema can be normalized to a specific form to prevent the possible occurrence of update anomalies....
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This note was uploaded on 11/01/2009 for the course CS cop4710 taught by Professor Dr. mark llewellyn during the Fall '09 term at University of Central Florida.

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chapter 19 - normalization - COP 4710 Database...

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