Concepts of Database Management, Fifth Edition Chapter 5: Database Design 1: Normalization

Objectives Discuss functional dependence Discuss primary keys Define first normal form, second normal form, and third normal form Describe the problems associated with tables (relations) that are not in first normal form, second normal form, or third normal form along with the mechanism for converting to all three Concepts of Database Management

Objectives Discuss the problems associated with incorrect conversions to third normal form Define fourth normal form Describe the problems associated with tables (relations) that are not in fourth normal form and describe the mechanism for converting to fourth normal form Understand how normalization is used in the database design process Concepts of Database Management

Normalization Normalization process – enables you to identify the existence of potential problems, called updating anomalies, in the design of a relational database Normal form – possesses a certain desirable collection of properties Concepts of Database Management

Figure 5.1: Premiere Products Data Concepts of Database Management

Functional Dependence Column B is functionally dependent on Column A if A’s value determines a single value for B at a given time Given A, a single value for B can be determined Concepts of Database Management

Functional Dependence Concepts of Database Management

Functional Dependence Example Figures 5.3-5.4: Functional Dependence Example Rep Table Where LastName can determine record Rep Table Where LastName cannot determine record Concepts of Database Management

Keys Column(s) C is primary key for table T if: Candidate Keys Property 1: All columns in T are functionally dependent on C Property 2: No subcollection of columns in C (assuming C is a collection of columns and not just a single column) also has Property 1 Candidate Keys Column(s) on which all other columns in table are functionally dependent Alternate Keys Candidate keys not chosen as primary keys Concepts of Database Management

First Normal Form (1NF) Unnormalized table Table in 1NF Contains a repeating group Table in 1NF Contains no repeating groups Removal of repeating groups is starting point in quest for problem-free tables Concepts of Database Management

Figure 5.5: 1NF Example Unnormalized Table Concepts of Database Management

Figure 5.6: 1NF Example (con’t.) Conversion to 1NF Concepts of Database Management

Second Normal Form (2NF) 1NF Tables may contain problems Redundancy Update Anomalies Update, inconsistent data, additions, deletions Occur because a column is dependent on a portion of a multi-column primary key 2NF Table In 1NF and no nonkey column is dependent on only a portion of the primary key Concepts of Database Management

Figure 5.7: Second Normal Form Concepts of Database Management

Update Anomalies Update Inconsistent data Additions Deletions Information is in multiple rows, difficult to update Inconsistent data Because of the duplication, a row that is not updated causes inconsistency Additions Dummy records are required to add new unused dependent rows Deletions Nonkey column (nonkey attribute) – when a column is not a part of the primary key Concepts of Database Management

Dependency Diagram Dependency diagram – uses arrows to indicate all the functional dependencies present in a table Partial dependencies – dependencies only on a portion of the primary key Concepts of Database Management

Dependency Diagram for Orders Figure 5.8: Dependency Diagram for Orders Concepts of Database Management

Third Normal Form (3NF) 2NF Tables may still contain problems Redundancy and wasted space Update Anomalies Update, inconsistent data, additions, deletions Occur because a column is dependent on a portion of a multi-column primary key 3NF Table In 2NF and the only determinants contained are candidate keys Concepts of Database Management

Figure 5.9: 2NF Example Concepts of Database Management

Figure 5.10: Sample Customer Data Concepts of Database Management

Customers Dependency Diagram Figure 5.11: Customers Dependency Diagram Concepts of Database Management

Incorrect Decomposition Decomposition must take place according to that described for 3NF Even though you may decompose a table, you run the risk of splitting the functional dependence across different tables Concepts of Database Management

Figure 5.12: 3NF Example Concepts of Database Management

Figure 5.13: Incorrect Decomposition Example Concepts of Database Management

Fourth Normal Form (4NF) 3NF Tables may still contain problems Dependencies Update Anomalies Update, additions, deletions Occur because of multivalued dependencies 4NF Table In 3NF and has no multivalued dependencies Concepts of Database Management

Figure 5.15: Incorrect 4NF Example Concepts of Database Management

Figure 5.16a: 4NF Example Concepts of Database Management

Figure 5.17: Normal Forms Concepts of Database Management

Summary Normalization is a process of optimizing databases to prevent update anomalies Normalization attempts to correct update issues by eliminating duplication Duplication also creates inconsistency Insertions can violate database integrity if the database is not normalized Deletions can violate database integrity if the database is not normalized Concepts of Database Management

Summary (con’t.) Normal Forms – First (1NF), Second (2NF), Third(3NF), and Fourth(4NF) 1NF has no repeating groups 2NF is in 1NF and no non-key column is dependent on only a portion of the primary key 3NF is in 2NF and the only determinants are candidate keys 4NF is in 3NF and has no multivalued dependencies Concepts of Database Management