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DATABASE DESIGN AND DEVELOPMENT: A VISUAL APPROACH

This chapter discusses the concepts of normalization and denormalization in database design, and the problems they can cause in terms of updates, inserts, and deletes. It also explains how to solve normalization violations and ensure data integrity.

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DATABASE DESIGN AND DEVELOPMENT: A VISUAL APPROACH

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  1. Chapter 4 DATABASE DESIGN AND DEVELOPMENT: A VISUAL APPROACH Raymond Frost – John Day – Craig Van Slyke Chapter 4 Normalization

  2. Chapter 4 Normalized vs. Denormalized Exhibit 4-1: Arcade Database Normalized vs. Denormalized Design

  3. Chapter 4 Denormalized Sample Data *note the duplicate entries Exhibit 4-2: Arcade Database Denormalized Sample Data

  4. 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? Exhibit 4-3: Arcade Database Update Problems Due to Duplicate Data

  5. Chapter 4 Normalized Design Eliminates Update Problems Exhibit 4-4: Arcade Database No Update Problem in Normalized Data

  6. 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. Exhibit 4-5: Arcade Database Insert Problem Due to Duplicate Data

  7. Chapter 4 Normalized Design Eliminates the Insert Problem Exhibit 4-6: Arcade Database No Insert Problem in Normalized Design

  8. 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 McGann’s member data. Exhibit 4-7: Arcade Database Delete Problem Due to Duplicate Data

  9. Chapter 4 Normalized Design Eliminates the Delete Problem Now, deleting visit 005 would not cause the loss of Sean McGann’s member data. Exhibit 4-8: Arcade Database No Delete Problem in Normalized Design

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

  11. 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

  12. Chapter 4 Solving a 1NF Violation Step 1: Tables • Since the phone number column violated the 1NF 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). Exhibit 4-10: Arcade Database Solving the 1NF Violation

  13. Chapter 4 Tables in 1NF Eliminate Repeating Data Problems Now all tables have fields that contain only single values. Exhibit 4-11: 1NF Solution with Sample Data

  14. 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. Exhibit 4-12: Primary Key Determines Non-key Fields

  15. 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. Exhibit 4-13: Email Acts as a Determinant Exhibit 4-14: Email Fails to Act as a Determinant

  16. Chapter 4 Second Normal Form (2NF) 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: 2NF Violation

  17. Chapter 4 Update Problem Caused by 2NF Violation Data not determined by the whole primary key will be duplicated and 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. Exhibit 4-16: 2NF Violation Creates Update Problem

  18. Chapter 4 Solving a 2NF 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. Exhibit 4-17: Enrollment Database Solving the 2NF Violation

  19. 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. Exhibit 4-18: Keys Are Now the Only Determinants

  20. Chapter 4 2NF 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: 2NF Solution with Sample Data

  21. Chapter 4 Third Normal Form (3NF) 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: 3NF Violation

  22. Chapter 4 Update Problem Caused by 3NF Violation By including both member information and visit information in the same table, not all non-key fields are determined by the primary key. Exhibit 4-21: 3NF Violation Creates Update Problem

  23. Chapter 4 Solving a 3NF 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: 3NF Solution

  24. 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. Exhibit 4-23: 3NF Solution – Keys Are Now the Only Determinants

  25. Chapter 4 3NF Solution With Sample Data All the non-key fields are determined only by the primary key. Exhibit 4-24: 3NF Solution with Sample Data

  26. 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

  27. 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. Exhibit 4-26: BCNF Violation Creates Update Problem

  28. 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

  29. 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. Exhibit 4-28: BCNF Solution – Keys Are Now the Only Determinants

  30. 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 Data

  31. Chapter 4 Fourth Normal Form (4NF) 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: 4NF Violation

  32. Chapter 4 Update Problem Cause by a 4NF 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. Exhibit 4-31: 4NF Violation Creates Update Problem

  33. Chapter 4 Solving a 4NF 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: 4NF Solution

  34. 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. Exhibit 4-33: 4NF Solution – Only One MVD per Table

  35. Chapter 4 4NF Solution with Sample Data Now Luce’s German certification can be dropped without losing his sports information. Exhibit 4-34: 4NF Solution with Sample Data

  36. Chapter 4 Detecting Normalization Violations These are the conditions under with each type of violation can occur. Exhibit 4-35: Necessary Conditions for Normal Form Violations

  37. Chapter 4 ER Diagram for Practice Exercise 1 Exhibit 4-36: ER Diagram for Practice Exercise 1

  38. Chapter 4 ER Diagram for Practice Exercise 2 Exhibit 4-37: ER Diagram for Practice Exercise 2

  39. Chapter 4 ER Diagram for Practice Exercise 3 Exhibit 4-38: ER Diagram for Practice Exercise 3

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