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Functional Dependencies for Relational Databases

Functional Dependencies for Relational Databases. Informal Design Guidelines - informal measures of quality Semantics of attributes Reducing redundant values in tuples Reducing null values in tuples Disallowing spurious tuples Functional Dependencies. Functional Dependencies - Definitions.

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Functional Dependencies for Relational Databases

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  1. Functional Dependencies for Relational Databases • Informal Design Guidelines - informal measures of quality • Semantics of attributes • Reducing redundant values in tuples • Reducing null values in tuples • Disallowing spurious tuples • Functional Dependencies

  2. Functional Dependencies - Definitions • X functionally determines Y if and only if each X value in a relationship R has associated with it precisely one Y value in R. • Whenever two tuples of R agree on their X value, they also agree on their Y value. Date, p. 272

  3. COURSE X TEACHER COURSE TEXT X Does ( ) ? TEXT COURSE TEACH Relation Elmasri, p. 306

  4. Why? • Teacher does not guarantee one and only one course or text • Course does not determine one and only one teacher or text • Need more information for text determining one and only one teacher/text. If only this data, OK

  5. Armstrong’s Inference Rules-like rules in Elmasri Date, p. 275; Elmasri p. 307

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