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: ² The logical "user view" level ² The storage "base relation" level ± Design is concerned mainly with base relations ± Criteria for "good" base relations: ² Discuss informal guidelines for good relational design ² 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 ² Only foreign keys should be used to refer to other entities ² Entity and relationship attributes should be kept apart as much as possible ² 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 ² Information is stored redundantly wasting storage ² 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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This note was uploaded on 05/01/2011 for the course ECON 102 taught by Professor Erus during the Fall '09 term at Boğaziçi University.

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ch14a - Informal Design Guidelines for Relational Databases...

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