CS338 Lecture Notes - Lecture 13: Functional Dependency, Data Redundancy, Database Design
24 Apr 2019
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Document Summary
How to measure fit of attributes types into a single relation: amount of redundant information in tuples, amount of null values in tuples, possibility of generating spurious tuples. Mis-packaged attributes every tuple includes employee data & department data redundancy: dept name and manager id repeated for every employee in the dept. Potential for too many null values: employees not in any department need to pad tuples with nulls. Update anomalies: deleting last employee in a dept should not delete dept, changing dept name/ manager requires updates to many tuples inserting employees requires checking for consistency of its dept name and manager. Design relational db schema so that every fact can be stored in one and only one tuple. Each actor has a unique date and city of birth. Given name only one value for birth and city. However, given birth year, cannot find a unique name or city. From example may or may not determine name or birth from city.
