lec08.366

lec08.366 - Winter 2008 CPE/CSC 366 Database Modeling...

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Unformatted text preview: . . Winter 2008 CPE/CSC 366: Database Modeling, Design and Implementation Alexander Dekhtyar . . Theory of Normal Forms Overview What is a Normal Form? A normal form of a database is a collection of conditions (constraints) on the database schema. If the database schema satisfies these conditions, we say that the database is in the normal form . Normal Forms in a nutshell. Brief descriptions of normal forms. • First Normal Form (1NF): no repeated attribute groups, atomic values of all attributes. • Second Normal Form (2NF): attributes depend on entire keys. • Third Normal Form (3NF): no inderect dependencies. • Boyce-Codd Normal Form (BCNF): all functional dependencies involve su- perkeys. • Fourth Normal Form (4NF): no redundant independent multiple many-to- many relationships. • Fifth Normal Form (5NF)/Project-Join Normal Form (PJNF): semantically related multiple many-to-many relationships are isolated. • Domain-Key Normal Form (DKNF): only key and domain constraints are present in the relation. In the course, we study 1NF, 2NF, 3NF and BCNF . Higher forms of normal- ization (i.e., additional constraints on the structure of the database schema) are needed only on rare occasions. Why Normal Forms? Normal forms allow us to ensure that our database designs possess some de- sired properties. More importantly, normal forms eliminate database anoma- lies . 1 Database Anomalies. A database anomaly is a problem with database maintenance/management caused by the database schema . Some database anomalies are listed below. Redundancy: Same information may be repeated multiple times. This wastes disk space and may lead to wasted effort and inconsistencies when database is changed....
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lec08.366 - Winter 2008 CPE/CSC 366 Database Modeling...

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