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Functional Dependencies

Functional Dependencies. True for all table instances Cannot get FDs just from one table instance Business Rules (Assumptions). eName  NIN NIN = f(eName) NIN contractNo hours eName hNo hLoc 1135 C1024 16 Smith J H25 East Kilbride

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Functional Dependencies

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  1. Functional Dependencies • True for all table instances • Cannot get FDs just from one table instance • Business Rules (Assumptions)

  2. eName  NIN NIN = f(eName) NIN contractNo hours eName hNo hLoc 1135 C1024 16 Smith J H25 East Kilbride 1135 C1025 15 Smith J H4 Glasgow ….. ……. .. ……… …. ……………. 1160 C1024 16 Smith J H25 East Kilbride Incorrect: eName  NIN Correct: NIN  eName

  3. NIN  eName contractNo  hNo hNo  hLoc NIN, contractNo  hours NIN, contractNo  hours, eName, hNo, hLoc NIN, contractNo  All

  4. Primary Key NIN, contractNo NIN, contractNo  hours, eName, hNo, hLoc NIN, contractNo, hNo hours, eName, hLoc NIN, contractNo, hNo:Primary key? Candidate Key: A minimum set of attributes that uniquely identifies each occurrence of an entity type.

  5. Alternate Keys hours, eName, hNo contractNo, hNo NIN, hNo All Incorrect!

  6. Assumptions • Identify all non-trivial FDs NIN  eName contractNo  hNo hNo  hLoc NIN, contractNo  hours • Choose a PK: NIN, contractNo • List all Aks: NONE

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