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Relation Normalization (Chapter 14)

Relation Normalization (Chapter 14). Modification Anomalies. What are modification anomalies? Errors or inconsistencies that may result when a user attempts to update a relation. Types of anomalies. Insertion anomalies.

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Relation Normalization (Chapter 14)

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  1. Relation Normalization(Chapter 14)

  2. Modification Anomalies • What are modification anomalies? • Errors or inconsistencies that may result when a user attempts to update a relation. • Types of anomalies. • Insertion anomalies. • An independent piece of information cannot be recorded into a relation unless an irrelevant information must be inserted together at the same time • Update anomalies. • The update of a piece of information must occur at multiple locations, not required by the referential integrity rule. • Deletion anomalies • The deletion of a piece of information unintentionally removes other information.

  3. Normal Forms • Normal forms are classes of relations and the techniques for preventing anomalies. • Normal forms are classified by the type of modification anomalies that have been removed. • Types of normal forms: • First Normal Form (1NF). • Second Normal Form (2NF). • Third Normal Form (3NF). • Boyce-Codd Normal Form (BCNF). • Fourth Normal Form (4NF). • Fifth Normal Form (5NF). • Domain/Key Normal Form (DK/NF).

  4. First Normal Form (1NF) • A relation R is in 1NF if and only if all attribute domains contain atomic values only. • Any table meets the definition of a relation is said to be in first Normal form, i.e. a relation in relational schema is always in 1NF.

  5. Second Normal Form (2NF) • A relation is in 2NF if and only if it is in 1NF without partial dependencies. • Partial dependency • A dependency in which one or more non-key attributes are functionally dependent on part (but not all) of the key. • Two extreme cases • The primary key consists of only one attribute. • No non-key attributes exist in the relation.

  6. Third Normal Form • A relation R is in 3NF if: whenever A1 A2 … AnB is a nontrivial dependency, either {A1, …,An} is a superkey, or B is a member of some key. • A relation is in 3NF if: • it is in 2NF without transitive dependencies. • Transitive dependency • A functional dependency between two (or more) non-key attributes.

  7. Example SALES(Cust_ID, Name, Salesperson, Region) FDs: Cust_ID  Cust_ID Name Salesperson Region Salesperson Region

  8. Example SALES1(Cust_ID, Name, Salesperson) SPERSON(Selesperson, Region)

  9. Another Example SHIPMENT(Snum, Origin, Destination Distance) FDs: Snum  Snum Origin Destination Distance Origin Destination  Distance SHIPMENT(Snum, Origin, Destination) DISTANCE(OriginDestination Distance)

  10. Relation Normalization Question FDs: SID CID  Grade SID  Name Major CID  Text Major  Dept 1. What can be the primary key for above relation? 2. Decompose the above relation into 2NF then 3NF relations.

  11. Boyce-Codd Normal Form • A relation R is in BCNF if and only if: whenever nontrivial dependency A1 A2 … AnB1 B2 … Bm holds for R, it must be the case that {A1, A2, …, An} is a superkey for R. • BCNF is one of the most important normal forms. • Relations in BCNF have no anomaly in regards to functional dependencies.

  12. 1. Each students may major in several subjects. 2. For each major, a given student has only one adviser. 3. Each major has several advisors. 4. Each advisor advises only one major. 5. Each advisor advises several students in one major. StuId Major  Fname; Fname  Major

  13. Decomposition into BCNF 1. Set D = {R}; 2. While there is a relation Q in D that is not in BCNF do begin choose a relation Q in D that is not in BCNF; find a FD XY in Q that violates BCNF; Expand right side to include X+; replace Q in D by two relations (Q-X+)  X and X+; end;

  14. Remove transitive dependencies Remove non-atomic attributes Remove partial dependencies Remove remaining anomalies resulting from functional dependencies Tables 1NF 2NF 3NF BCNF

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