Chapter 4 DATABASE DESIGN AND DEVELOPMENT A VISUAL

Chapter 4 DATABASE DESIGN AND DEVELOPMENT: A VISUAL APPROACH Raymond Frost – John Day – Craig Van Slyke Chapter 4 Normalization 1 Database Design and Development: A Visual Approach © 2006 Prentice Hall

Chapter 4 Normalized vs. Denormalized Database Design and Development: A Visual Approach © 2006

Chapter 4 Denormalized Sample Data *note the duplicate entries Database Design and Development: A

Chapter 4 Denormalized Design Causes Update Problems When the password for Thom Luce was changed, it was not changed in both his entries. Which password is the correct password? Database Design and Development: A Visual Approach © 2006 Prentice Hall Exhibit 4 -3: Arcade Database Update Problems Due to Duplicate Data 4

Chapter 4 Normalized Design Eliminates Update Problems Database Design and Development: A Visual Approach

Chapter 4 Denormalized Design Creates Insert Problems A new member cannot be created unless they have already made a visit, otherwise there would be no primary key value. This field may not be left blank. Database Design and Development: A Visual Approach © 2006 Prentice Hall Exhibit 4 -5: Arcade Database Insert Problem Due to Duplicate Data 6

Chapter 4 Normalized Design Eliminates the Insert Problem Database Design and Development: A Visual

Chapter 4 Denormalized Design Creates Delete Problems If a member makes only one visit, deleting that record will cause the loss of the member data. Deleting visit 005 would cause the loss of Sean Mc. Gann’s member data. Database Design and Development: A Visual Approach © 2006 Prentice Hall Exhibit 4 -7: Arcade Database Delete Problem Due to Duplicate Data 8

Chapter 4 Normalized Design Eliminates the Delete Problem Now, deleting visit 005 would not cause the loss of Sean Mc. Gann’s member data. Database Design and Development: A Visual Approach © 2006 Prentice Hall Exhibit 4 -8: Arcade Database No Delete Problem in Normalized Design 9

Chapter 4 First Normal Form (1 NF) Definition: A table in which all fields contain a single value. The example above would be a violation of the 1 NF rule; therefore this table would have to be redesigned. Exhibit 4 -9: 1 NF Violation Database Design and Development: A Visual Approach © 2006 Prentice Hall 10

Chapter 4 Fixing Normalization Violations Step 1: Tables -Create new table(s) -Rename original table if necessary Step 2: Relationships - Establish relationships between original and new table(s) Step 3: Fields - Transfer fields and rename as needed Step 4: Keys - Choose PK and FK for all tables 11 Database Design and Development: A Visual Approach © 2006 Prentice Hall

Chapter 4 Solving a 1 NF Violation Step 1: Tables - Since the phone number column violated the 1 NF rule, make a new table to hold phone numbers: DIRECTORY. Step 2: Relationships - A member has multiple phone numbers and a phone number belongs to one member Step 3: Fields - The phone field is transferred to the DIRECTORY table Step 4: Keys - The email column in MEMBER becomes a FK (MEMBER$email) in DIRECTORY - The PK in DIRECTORY becomes MEMBER$email and phone since two members could have the same phone number (e. g. two members from the same household). Database Design and Development: A Visual Approach © 2006 Prentice Hall Exhibit 4 -10: Arcade Database Solving the 1 NF Violation 12

Chapter 4 Tables in 1 NF Eliminate Repeating Data Problems Now all tables have fields that contain only single values. Exhibit 4 -11: 1 NF Solution with Sample Database Design and Development: A Visual Approach © 2006 Prentice Hall 13

Chapter 4 Determinants Determinant: a field or group of fields that controls or determines the values in another field. The value of email will determine the values in all the other fields. That is, if you know someone’s email, you can determine the rest of their information. Database Design and Development: A Visual Approach © 2006 Prentice Hall Exhibit 4 -12: Primary Key Determines Non-key Fields 14

Chapter 4 Determinants and Duplicate Data When you have duplicate data, knowing someone’s email may not allow you to determine the rest of the data as shown below. Database Design and Development: A Visual Approach © 2006 Prentice Hall Exhibit 4 -13: Email Acts as a Determinant Exhibit 4 -14: Email Fails to Act as a Determinant 15

Chapter 4 Second Normal Form (2 NF) Definition: A table in which each non-key field is determined by the whole primary key and not part of the primary key by itself. In this example, once you know a student’s id, you can determine his or her name, dorm, and phone. Therefore, the fname, lname, dorm, and phone non-key fields are determined by just part of the primary key: id. Exhibit 4 -15: 2 NF Violation Database Design and Development: A Visual Approach © 2006 Prentice Hall 16

Chapter 4 Update Problem Caused by 2 NF Violation Data not determined by the whole primary key will be duplicated any updates may not be made to all instances of duplicate data. In this example, we no longer know the correct phone number for Jim Green. Database Design and Development: A Visual Approach © 2006 Prentice Hall Exhibit 4 -16: 2 NF Violation Creates Update Problem 17

Chapter 4 Solving a 2 NF Violation Step 1: Tables - Since only name, dorm, and phone belong in the STUDENT table, create a new table (ENROLL) for the registration information. Step 2: Relationships - A student can enroll in many sections but a particular student-section enrollment relates back to one student. Step 3: Fields - The SECTION$call_no and grade are information about the enrollment. Step 4: Keys - The id column in STUDENT becomes a FK (STUDENT$id) in ENROLL. - The PK in ENROLL becomes STUDENT$id and SECTION$call_no. Database Design and Development: A Visual Approach © 2006 Prentice Hall Exhibit 4 -17: Enrollment Database Solving the 2 NF Violation 18

Chapter 4 All Keys Are Now Determinants All the fields in the STUDENT table are determined by the id. In ENROLL, grade is determined by the student + section. Database Design and Development: A Visual Approach © 2006 Prentice Hall Exhibit 4 -18: Keys Are Now the Only Determinants 19

Chapter 4 2 NF Solution with Sample Data If you a student’s id, you can determine the values in fname, lname, dorm, and phone. If you know the id of a student and the call_no of a section, you can determine the value of grade. Exhibit 4 -19: 2 NF Solution with Sample Database Design and Development: A Visual Approach © 2006 Prentice Hall 20

Chapter 4 Third Normal Form (3 NF) Definition: A table in which none of the non-key fields determine another non-key field. In this example, once you know a member’s email, you can determine his or her password, name, and phone number. Therefore, the fname, lname, dorm and phone non-key fields are determined by just part of the primary key: id. Exhibit 4 -20: 3 NF Violation Database Design and Development: A Visual Approach © 2006 Prentice Hall 21

Chapter 4 Update Problem Caused by 3 NF Violation By including both member information and visit information in the same table, not all non-key fields are determined by the primary key. Database Design and Development: A Visual Approach © 2006 Prentice Hall Exhibit 4 -21: 3 NF Violation Creates Update Problem 22

Chapter 4 Solving a 3 NF Violation Step 1: Tables - Since only password, name, and phone belong in the MEMBER table, create a new table (VISIT) for the visit information. Step 2: Relationships - A member can make many visits, but a particular visit is associated with one member. Step 3: Fields - The id, date_time_in, and date_time_out are information about the visit, so move them to the VISIT table. Step 4: Keys - The email column becomes the PK in MEMBER. - The email column in MEMBER becomes a FK (MEMBER$email) in VISIT. - The PK in VISIT becomes the session id for the visit. Exhibit 4 -22: 3 NF Solution Database Design and Development: A Visual Approach © 2006 Prentice Hall 23

Chapter 4 Keys Are Now Determinants All the fields in the MEMBER table are determined by email. In VISIT, all non-key fields are determined by id and email. Database Design and Development: A Visual Approach © 2006 Prentice Hall Exhibit 4 -23: 3 NF Solution – Keys Are Now the Only Determinants 24

Chapter 4 3 NF Solution With Sample Data All the non-key fields are determined only by the primary key. Exhibit 4 -24: 3 NF Solution with Sample Database Design and Development: A Visual Approach © 2006 Prentice Hall 25

Chapter 4 Boyce-Codd Normal Form (BCNF) Definition: Every determinant is a key. In this example, there are two fields that could be determinants for an employee: employee_id and ssn. Exhibit 4 -25: BCNF Violation Database Design and Development: A Visual Approach © 2006 Prentice Hall 26

Chapter 4 Update Problem Caused by a BCNF Violation Since ssn is a non-key field in this table, it can be easily updated, causing incorrect data. Database Design and Development: A Visual Approach © 2006 Prentice Hall Exhibit 4 -26: BCNF Violation Creates Update Problem 27

Chapter 4 Solving a BCNF Violation Step 1: Tables - Since ssn is really information about the employee, it needs to be in the EMPLOYEE table. Step 2: Relationships - An employee can get many bonuses but a particular bonus belongs to just one employee. Step 3: Fields - Move the ssn field into the EMPLOYEE table. Step 4: Keys - The primary key for the EMPLOYEE table is the employee’s id. Exhibit 4 -27: BCNF Solution Database Design and Development: A Visual Approach © 2006 Prentice Hall 28

Chapter 4 Keys Are Now Determinants All the fields in the EMPLOYEE table are determined by id. In QUARTERLY_BONUS, all non-key fields are determined by id and quarter. Database Design and Development: A Visual Approach © 2006 Prentice Hall Exhibit 4 -28: BCNF Solution – Keys Are Now the Only Determinants 29

Chapter 4 BCNF Solution With Sample Data All the non-key fields are determined only by the primary key Exhibit 4 -29: BCNF Solution With Database Design and Development: A Visual Approach © 2006 Prentice Hall 30

Chapter 4 Fourth Normal Form (4 NF) Definition: In an all-key table, part of the key can determine multiple values of, at most, one other field. In this example, email can determine multiple languages or sports associated with an employee. The double-headed arrow indicates a multivalued dependency: one field determining multiple values of another field. Exhibit 4 -30: 4 NF Violation Database Design and Development: A Visual Approach © 2006 Prentice Hall 31

Chapter 4 Update Problem Cause by a 4 NF Violation We could not drop Luce’s German certification without losing his sports information since the primary key requires that all three fields have a value. Database Design and Development: A Visual Approach © 2006 Prentice Hall Exhibit 4 -31: 4 NF Violation Creates Update Problem 32

Chapter 4 Solving a 4 NF Violation Step 1: Tables - Email must be associated with both languages and sports, so create two new tables: LANGUAGE and SPORT. Step 2: Relationships - These tables would not be directly related, but rather, would be related separately to a member table. Step 3: Fields - Put language and sport in separate tables each time paired with email. Step 4: Keys - The primary key for the LANGUAGE table is email and language, - The primary key for the SPORT table is email and sport. Exhibit 4 -32: 4 NF Solution Database Design and Development: A Visual Approach © 2006 Prentice Hall 33

Chapter 4 No More Than One Multi-Valued Determinant Each all-key table only has one part of the key that determines multiple values another field. Database Design and Development: A Visual Approach © 2006 Prentice Hall Exhibit 4 -33: 4 NF Solution – Only One MVD per Table 34

Chapter 4 4 NF Solution with Sample Data Now Luce’s German certification can be dropped without losing his sports information. Exhibit 4 -34: 4 NF Solution with Sample Database Design and Development: A Visual Approach © 2006 Prentice Hall 35

Chapter 4 Detecting Normalization Violations These are the conditions under with each type of violation can occur. Database Design and Development: A Visual Approach © 2006 Prentice Hall Exhibit 4 -35: Necessary Conditions for Normal Form Violations 36