January/February 2011

Transcription

1 CLASS DISCUSSION AND NOTES January/February 2011 Mon Tue Wed Thu Fri 31 Feb AH-2 (individual) Chap. 3 Rel. Model & Normalization AH-3 (team) Chap. 4 DB Design Using Normalization

2 COURSE OVERVIEW I. GETTING STARTED II. DATABASE DESIGN & IMPLEMENTATIO III. SELECTED TOPICS Introduction (C-1) Introduction to Structured Query Language (C-2) Relational Model and Normalization Database Design and Normalization (C-4) Data Modeling with the ER Model (C-5) Transforming Data Models into Database Designs (C-6) Managing Multiuser Databases (C-9) XML (C-12) SQL for Database Construction (C-7)

3 MODULE II: DATABASE DESIGN & IMPLEMENTATION Part 3: Relational Model and Normalization (Text: Chapter 3) NOTES FOR CLASS SESSION STARTING POINTS Questions to begin our deliberation 1. Why is it important to learn design of databases from existing data? 2. What theory can you use to judge the advantages and disadvantages of a certain database design? Student Learning Objectives (Desired Outcomes) At the end of in-class and outside-class work on this topic, you should be able to: 1. Explain basic relational terminology. [Comprehension] 2. Explain the characteristics of relations. [Comprehension] 3. Describe alternative terminology used in describing the relational model. [Comprehension]

4 4. Identify functional dependencies and identify determinants and dependent attributes. [Comprehension] 5. Identify primary, candidate, and composite keys. [Comprehension] 6. Identify possible insertion, deletion, and update anomalies in a relation. [Comprehension] 7. Place a relation in BCNF normal form. [Application] 8. Identify multivalued dependencies. [Comprehension] 9. Place a relation in 4th normal form. [Application] QUESTIONS TO EXPLORE READINGS Q 1. Why is it important to evaluate the design of tables stored in a database? Q 2. What is the basic goal of normalization? Q 3. What exactly is meant for an attribute to be a determinant? Q 4. What exactly is meant by functional dependency? Q 5. What is meant by the normal forms, BCNF and 4NF? In Class Team Exercise Set 3

5 Text Chapter 3: The Relational Model and Normalization Points to consider (Please take time review all the points before starting the exercise): 1. An entity is some identifiable thing that users want to track (An entity normally gets converted to a table in a database. For e.g., USER, BOOK, ORDER, etc.). 2. A relation is a two-dimensional table that has the following characteristics: a. Rows contain data about an entity. b. Columns contain data about attributes of the entity. c. All entries in a column are of the same kind. d. Each column has a unique name. e. Cells of the table hold a single value. f. The order of the columns is unimportant. g. The order of the rows is unimportant. h. No two rows may be identical. 3. A functional dependency occurs when the value of one (a set of) attribute(s) determines the value of a second (set of) attribute(s) (for e.g., with the help of SSN we can determine the name of a person). 4. A candidate key is a key that determines all of the other columns in a relation. 5. A primary key is a candidate key selected as the primary means of identifying rows in a relation. 6. A surrogate key as an artificial column added to a relation to serve as a primary key. 7. A foreign key is the primary key of one relation that is placed in another relation to form a link between the relations.

6 8. 1NF A table that qualifies as a relation is in 1NF (Refer to point 2). 9. 2NF A relation is in 2NF if and only if all of its non-key attributes are dependent on all of the primary key attributes NF A relation is in 3NF if and only if it is in 2NF and there are no non-key attributes determined by another nonkey attribute. 11. Boyce-Codd Normal Form (BCNF) A relation is in BCNF if and only if every determinant is a candidate key. 12. A multivalued dependency occurs when a determinant determines a particular set of values. Exercise Set: Consider the following table structure. It was created by a novice database designer. Though the structure is capable enough to hold all the data, it lacks some design elegance. Please modify the table structure by applying the design principles you have learnt. RacerNa TeamNa DateTeamRegis DateRacerRegist Paid me me tered ered John BMW 01/01/09 02/01/09 Yes Martin Mercedes 05/01/09 06/01/09 No The (values in) column DateTeamRegistered can be identified from TeamName The column DateRacerRegistered can be identified only with RacerName and TeamName The column Paid can be identified only with RacerName and TeamName

7 1. Does the above table have all the desired characteristics of a Relation? (Refer to point 2 and write your answer.) 2. Find the functional dependency or composite functional dependencies in the table. 3. Find out if the table is in BCNF. If not please decompose the table into tables that are in BCNF. Hint: 4. Identify the primary keys, candidate keys and foreign keys in the tables identified for the previous question. 5. What are the advantages of using BCNF form for the above given problem? (Team) Take Home Assignment Set 3 Text Chapter 3: The Relational Model and Normalization This assignment is a continuation of the previous take-home assignment. Please read the solution for the previous assignment before starting this one. The following are three relations (without any relationship among them) designed for little John s book store.

8 USER_TABLE (FirstName, LastName, , CreditCardNumber, PhoneNumber, ShippingAddress1, ShippingAddress2, ShippingCity, ShippingState, ShippingZip, Password) FirstName LastName CreditCardNumber PhoneNumber ShippingAddress1 ShippingAddress2 ShippingCity ShippingState ShippingZip Password Saravanaraj Duraisamy sduraisam Lenox rd Apt 111 Atlanta GA Password1 Roger Federer Lenox Rd Apt 001 Atlanta GA Password2 Rafael Nadal Lenox Rd Apt 002 Atlanta GA Password3 John Travolta Lenox Rd Apt 003 Atlanta GA Password4 BOOK_TABLE (ISBN, Title, Price, PublicationYear, Description, AvailableCount, AuthorFirstName, AuthorLastName, Category, Publisher) ORDER_TABLE (OrderNumber, , ISBN, OrderDate, Status, Quantity, OrderCost) John wants to make certain modification to his table schema so that every order can accommodate multiple order items (in a single order, any customer can buy multiple items). He designed the following table for ORDER_TABLE. ORDER_TABLE (OrderNumber, , ISBN, OrderDate, Status, OrderQuantity, OrderCost, OrderItemNumber, OrderItemQuanity, OrderItemCost)

9 OrderNumber ISBN OrderDate Status OrderQuantity OrderCost OrderItemNumber OrderItemQuantity OrderItemCost 1 sduraisamy1@ Shipped sduraisamy1@ Shipped rfederer1@stu NotShipped State the Primary key/candidate key in the newly proposed ORDER_TABLE which can accommodate multiple Order items for each Order. List the functional and multivalued functional dependencies. 2. Explain if the newly proposed ORDER_TABLE is in BCNF format. If it is not in BCNF make the needed modifications. 3. Please state the conditions under which the following are true: (FirstName, ShippingAddress1) LastName (ShippingAddress1, ShippingAddress2, ShippingZip) (FirstName, LastName)