Normalization2 - Normalization Dongsheng Lu Feb 21, 2003...

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Unformatted text preview: Normalization Dongsheng Lu Feb 21, 2003 Chapter Objectives The purpose of normailization Data redundancy and Update Anomalies Functional Dependencies The Process of Normalization First Normal Form (1NF) Second Normal Form (2NF) Third Normal Form (3NF) Chapter Objectives (2) General Definition of Second and Third Normal Form Boyce-Codd Normal Form (BCNF) Fourth Normal Form (4NF) Fifth Normal Form (5NF) The Purpose of Normalization Normalization is a technique for producing a set of relations with desirable properties, given the data requirements of an enterprise. 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. Update Anomalies Relations that have redundant data may have problems called update anomalies , which are classified as , Insertion anomalies Deletion anomalies Modification anomalies Example of Update Anomalies To insert a new staff with branchNo B007 into the StaffBranch relation; To delete a tuple that represents the last member of staff located at a branch B007; To change the address of branch B003. staffNo sName position salary branchNo bAddress SL21 John White Manager 30000 B005 22 Deer Rd, London SG37 Ann Beech Assistant 12000 B003 163 Main St,Glasgow SG14 David Ford Supervisor 18000 B003 163 Main St,Glasgow SA9 Mary Howe Assistant 9000 B007 16 Argyll St, Aberdeen SG5 Susan Brand Manager 24000 B003 163 Main St,Glasgow SL41 Julie Lee Assistant 9000 B005 22 Deer Rd, London StaffBranch Figure 1 StraffBranch relation Example of Update Anomalies (2) staffNo sName position salary branceNo SL21 John White Manager 30000 B005 SG37 Ann Beech Assistant 12000 B003 SG14 David Ford Supervisor 18000 B003 SA9 Mary Howe Assistant 9000 B007 SG5 Susan Brand Manager 24000 B003 SL41 Julie Lee Assistant 9000 B005 branceNo bAddress B005 22 Deer Rd, London B007 16 Argyll St, Aberdeen B003 163 Main St,Glasgow Figure 2 Straff and Branch relations Staff Branch Functional Dependencies Functional dependency describes the relationship between attributes in a relation. For example, if A and B are attributes of relation R, and B is functionally dependent on A ( denoted A B), if each value of A is associated with exactly one value of B. ( A and B may each consist of one or more attributes.) A B B is functionally dependent on A Determinant Refers to the attribute or group of attributes on the left-hand side of the arrow of a functional dependency Trival functional dependency means that the right-hand side is a subset ( not necessarily a proper subset) of the left- hand side. Functional Dependencies (2) For example: (See Figure 1) staffNo, sName sName staffNo, sName staffNo They do not provide any additional information about possible integrity constraints on the values held by these attributes....
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Normalization2 - Normalization Dongsheng Lu Feb 21, 2003...

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