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Normalization Chapter Transparencies
Last Class
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Access Lab
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Today
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Normalization How can we create a table? Is there any potential problems? If there is problems, can we fix those problems?
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Chapter 13 - Objectives
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Purpose of normalization. Problems associated with redundant data. Identification of various types of update anomalies such as insertion, deletion, and modification anomalies. How to recognize appropriateness or quality of the design of relations.
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Chapter 13 - Objectives
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How functional dependencies can be used to group attributes into relations that are in a known normal form.
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Normalization
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Main objective in developing a logical data model for relational database systems is to create an accurate representation of the data, its relationships, and constraints. To achieve this objective, must identify a suitable set of relations.
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Normalization
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Four most commonly used normal forms are first (1NF), second (2NF) and third (3NF) normal forms, and BoyceCodd normal form (BCNF). Based on functional dependencies among the attributes of a relation. A relation can be normalized to a specific form to prevent possible occurrence of update anomalies.
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Data Redundancy
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Major aim of relational database design is to group attributes into relations to minimize data redundancy and reduce file storage space required by base relations. Problems associated with data redundancy are illustrated by comparing the following Staff and Branch relations with the StaffBranch relation.
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Data Redundancy
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Data Redundancy
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StaffBranch relation has redundant data: details of a branch are repeated for every member of staff. In contrast, branch information appears only once for each branch in Branch relation and only branchNo is repeated in Staff relation, to represent where each member of staff works.
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Update Anomalies
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Relations that contain redundant information may potentially suffer from update anomalies. Types of update anomalies include: Insertion, (new staff StaffBranch)
in Insert new branch with no staff.
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Deletion,
Delete the last staff from a branch loose information
Modification.
Address change in B003
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Functional Dependency
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Main concept associated with normalization. Functional Dependency Describes relationship between attributes in a relation. If A and B are attributes of relation R, B is functionally dependent on A (denoted A B), if each value of A in R is associated with exactly one value of B in R.
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Functional Dependency
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Property of the meaning (or semantics) of the attributes in a relation. Diagrammatic representation:
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Determinant of a functional dependency refers to attribute or group of attributes on left-hand side of the arrow.
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Example - Functional Dependency
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Example- StaffBranch
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StaffNo sName, position, salary, branchNo, bAddress branchNo bAddress bAddress branchNo branchNo, position salary bAddress, position salary
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StaffNo sName, position, salary, branchNo, bAddress xbranchNo bAddress xbAddress branchNo xbranchNo, position salary xbAddress, position salary
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Functional Dependency
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Main characteristics of functional dependencies used in normalization: have a 1:1 relationsh...