Lecture 05 - Lecture 05 Comp355 Data Normalization...

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Lecture 05 Comp355
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Data Normalization Primarily a tool to validate and improve a logical design so that it satisfies certain constraints that avoid unnecessary duplication of data The process of decomposing relations with anomalies to produce smaller, well-structured relations
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Well-Structured Relations A relation that contains minimal data redundancy and allows users to insert, delete, and update rows without causing data inconsistencies Goal is to avoid anomalies Insertion Anomaly –adding new rows forces user to create duplicate data Deletion Anomaly –deleting rows may cause a loss of data that would be needed for other future rows Modification Anomaly –changing data in a row forces changes to other rows because of duplication General rule of thumb: A table should not pertain to more than one entity type
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Example–Figure 5-2b Question–Is this a relation? Answer–Yes: Unique rows and no multivalued attributes Question–What’s the primary key? Answer–Composite: Emp_ID, Course_Title
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Anomalies in this Table Insertion –can’t enter a new employee without having the employee take a class Deletion –if we remove employee 140, we lose information about the existence of a Tax Acc class Modification
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This note was uploaded on 04/07/2008 for the course COMP 355 taught by Professor Wu during the Spring '08 term at Wentworth Institute of Technology.

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Lecture 05 - Lecture 05 Comp355 Data Normalization...

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