Normalization of Database Lecture - ANS Yong Choi School of Business CSUB

2 1NF Example Unnormalized Table PK

3 1NF Example (con’t.) Conversion to 1NF PK

4 Another 1NF Example Cust_IDNameStreetPhone 104Mr. Ray Suchecki 123 Pond Hill Road, Detroit, MI, (313) Cust_IDSalesRep_NameRep_OfficeOrder_1Order_2Order_3 1022Jones PK

5 2NF Example PK Each arrow shows partial dependency

6 2NF Example

7 Example of 3NF PK: Cust_ID

8 Relation with transitive dependency PK

9 Transitive dependency All attributes are functionally dependent on Cust_ID. –Cust_ID -> Name –Cust_ID -> Salesperson –Cust_ID -> Region However, there is a transitive dependency. –Region is functionally dependent on Salesperson. –Salesperson -> Region

10 Problems with Transitive dependency A new sales person (Yong) assigned to the North region cannot be entered until a customer has been assigned to that salesperson (since a value for Cust_ID must be provided to insert a row in the relation). If customer number 6837 is deleted from the table, we lose the information that salesperson Hernandez is assigned top the Easy region. If sales person Smith is reassigned to the East region, several rows must be changed to reflect that fact.

11 Decomposing the SALES relation

12 Relations in 3NF Now, there are no transitive dependencies… Both relations are in 3 rd NF CustID  Name CustID  Salesperson Salesperson  Region

13 Dependency Diagram

14 Boyce-Codd Normal Form (BCNF) Special case of 3NF. A relation is in BCNF if it’s in 3NF and there is no hidden dependencies. Below is in 3NF but not in BCNF

15 BCNF Stu_IDAdvisorMajorGPA 123NasaPhysics ElvisMusic KingLiterature JacksonMusic NasaPhysics3.5 Student

16 BCNF Stu_IDAdvisorMajorGPA Don’t confuse with Transitive Dependency! Advisor is functionally dependent on Major.

17 BCNF In Physics the advisor Nasa is replaced by Einstein. This change must be made in two ( or more) rows in the table. If we want to insert a row with the information that Choi advises in MIS. This cannot be done until at least one student majoring in MIS is assigned Choi as an advisor. If student number 789 withdraw from school, we lose the information that Jackson advises in Music.

18 Conversion to BCNF Stu_IDAdvisorGPA 123Nasa Elvis King Jackson Nasa3.5 AdvisorMajor NasaPhysics ElvisMusic KingLiterature JacksonMusic Student Advisor

19 Decomposition into BCNF

20 3NF and BCNF In practice, most relation schemas that are in 3NF are also in BCNF. Only if a hidden dependency X -> A exists in a relation. In general, it is best to have relation schemas in BCNF. If that is not possible, 3NF will do. However, 2NF and 1NF are not considered good relation schema designs.

21 4NF A relation is in 4NF if it is already in 3NF and does not contain two multi-valued dependencies that are independent.- it’s a different meaning than not having multi- valued attributes for 1NF. e.g., Smith can cook and type. Smith speaks French, German, and Greek

22 4NF E_NameSkillLanguage Smithcooknull Smithtypenull SmithnullFrench SmithnullGerman SmithnullChinese E-Name ->-> Skill E-Name ->-> Language PK

23 4NF The values for Skill and the values for Language are independent. E_NameSkillE_NameLanguage SmithCookSmithFrench SmithTypeSmithGerman SmithChinese PK

24 Faculty (A) relation FacultyNumStudentNumCommitteeCode ADV HSG PER HSG CUR Faculty (A) – normalized table

25 Faculty (A) relation Each FacultyNum has a well-defined set of StudentNums. Each FacultyNum has a well-defined set of CommitteeCodeses. The STUDENTNUM and the COMMITTEECODE are independent of each other.

26 Faculty (B) relation Faculty (B)

27 Faculty (B) relation Has a composite PK –FacultyNum, StudentNum, and CommitteeCode Since there are no determinants other than the PKs, the relation is in BCNF. Yet it does contain much redundant data that can easily lead to update anomalies because of multi-valued dependencies.

28 Problems with Faculty (B) relation Changing the CommitteeCode for faculty member requires more than one change. Suppose that a new faculty member 555 but does not yet serve on any committee. When a facultyNum 555 begins advising student 44332, there is a problem because the CommitteeCode is a part of PK. If faculty member 444 no longer advises student and delete appropriate record from the relation, we lose the information that faculty member serves on the Housing committee (HSG).

29 Conversion to 4NF