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Normal Forms

Normal Forms. By Christopher Archibald October 16 th 2007. Overview. Database Normalization 1 st Normal Form 2 nd Normal Form 3 rd Normal Form Boyce- Codd Normal Form (BCNF) Lossless-Join. Normalization. Normalization is a technique for designing relational table to:

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Normal Forms

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  1. Normal Forms By Christopher Archibald October 16th 2007

  2. Overview • Database Normalization • 1st Normal Form • 2nd Normal Form • 3rd Normal Form • Boyce- Codd Normal Form (BCNF) • Lossless-Join

  3. Normalization • Normalization is a technique for designing relational table to: • Minimize duplication of information • Reduce the potential for data anomalies

  4. Normal Form • Normal forms provide a stepwise progression toward the goal of fully normalized relation schema that are free for data redundancies.

  5. First Normal Form (1NF) • 1NF definition: A schema R is in 1NF only when the attributes comprising the schema are atomic and single-valued • No Multi-valued attributes • No composite attributes • No repeating groups (2 columns can not store similar information) • Can’t have a Null Attribute • Must have a Primary Key

  6. First Normal Form Example • This is in 1NF (Has primary Key, no repeating group, No Null attributes and No multivariable • What happens if James gets a Second Phone Number?

  7. First Normal FormExample • No longer in 1NF because Telephone Number has a multivariable. • Now we need to redesign our table

  8. First Normal FormExample • Not in First Normal forum • Tel. No. 3 is a null attribute • Tel. No. 1-2 repeat similar information (Repeating group)

  9. First Normal Form • This is in First Normal Form • Telephone Number is no long a repeating group • No Multivariable • No Null Attributes • Has a Primary Key

  10. Second Normal Form (2NF) • 2NF Definition: A relation schema R is in 2NF if every non-prime attribute in R is fully functionally dependent on the primary key of R. • Must be 1NF • An Attribute that is not part of the candidate key must be dependent on the candidate key and not a part of the candidate key

  11. Second Normal FormExample • Only Candidate key is (Employee, Skill) • Not in 2NF • Current Work Location is dependent on Employee • Can Cause an Anomaly Updating Jones Work location for Typing and Shorthand but not Whittling. Then asking “What is Jones current work location”, can cause a contradictory answer, because there are 2 different locations.

  12. Second Normal Form Example • Both tables are in 2NF • Meets 1NF requirements • No non-primary key attribute is dependent on part of a key.

  13. 1NF and 2NF • 1NF and 2NF remove most anomalies • Following table is in 2NF • There is redundancy under Winner/Winner DoB • Al Fredrickson and Chip Masterson • Can cause an anomaly

  14. Third Normal Form (3NF) • 3NF Definition: A relation schema R is in 3NF if no non-prime attribute is functionally dependent on another non-prime attribute in R • Table must be in 2NF • Eliminate field that do not depended on the primary key by placing them in different tables

  15. Third Normal FormExample • Table is in 2NF but fails to meet 3NF • Winner Date of Birth is Dependent on Winner • If Al Fredrickson Date of birth is update in the first row but not the second ask, “What Al Fredrickson Date of birth” will result in 2 different dates.

  16. Third Normal FormExample • Table is in 3NF • Meets 1NF and 2NF • No non-primary Key attribute is Dependent on another non-primary Key attribute • Update Anomalies cannot occur in these tables

  17. Boyce-Codd Normal Form (BCNF) • BCNF Definition: A relation Schema R is in BCNF if for every non-trivial functional dependency in R, the determinant is a superkey of R • Does not allow Functional Dependency that is not part of a Candidate key • Most 3NF meet the requirement of a BCNF

  18. Boyce-Codd Normal FormExample • Candidate key (Tutor ID, Student ID) And (SSN, Student ID) • Table is in 3NF, but not BCNF • SNN is dependent on Tutor ID but (Tutor id, SNN) is not a Candidate key

  19. Other Normal Forms • There is also • Fourth normal form • Fifth normal Form • Domain/key Normal form • Sixth normal form • Which will be covered in chapter 9

  20. Lossless-Join Decomposition • The principle behind Lossless-Join decomposition is that the decomposition of a relation schema, R, should be strictly reversible, i.e. • When we break tuples in to different tables for normalization we should be able to combined them and get what we started

  21. Lossless-Join Decomposition

  22. Lossless-Join Decomposition

  23. Lossless-Join Decomposition

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