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ch14a - Informal Design Guidelines for Relational Databases...

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Informal Design Guidelines for Relational Databases Relational database design: The grouping of attributes to form "good" relation schemas Two levels of relation schemas: The logical "user view" level The storage "base relation" level Design is concerned mainly with base relations Criteria for "good" base relations: Discuss informal guidelines for good relational design Discuss formal concepts of functional dependencies and normal forms 3NF, BCNF
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Semantics of the Relation Attributes Each tuple in a relation should represent one entity or relationship instance Only foreign keys should be used to refer to other entities Entity and relationship attributes should be kept apart as much as possible Design a schema that can be explained easily relation by relation. The semantics of attributes should be easy to interpret.
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Redundant Information in Tuples and Update Anomalies Mixing attributes of multiple entities may cause problems Information is stored redundantly wasting storage Problems with update anomalies: z Insertion anomalies z Deletion anomalies z Modification anomalies
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EXAMPLE OF AN UPDATE ANOMALY Consider the relation:
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