Chapter Three

Objectives Identification of Keys Application of primary and foreign keys Converting a database design to Relational DB.What is a good DBMS

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Keys: (Constraints)

A set of attributes whose values uniquely identify each entity in an entity set.

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Keys: (Constraints)

Primary key: A key selected by the Database Administrator

Characteristics of primary key:a. Uniqueness:

At any given time, no two tuples can have the same value for a given primary key

Example:

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Keys: (Constraints)

b. Minimally:None of the attributes in primary key

can be discarded without distorting the uniqueness property

Example:

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Keys: (Constraints)

Foreign key:An attribute(s) in an entity set (relation)

which is the primary key of other entity set (relation)

Example: Department(Name, Dept_Id, ….) Faculty(Name, Id, Dept_Id,…)

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Practice:

Identify the primary keys and foreign keys in your video store project.

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Normal Forms (Guidelines for RD design)

How do we know this design is good?

If it is not a good design, What should we do?

Modify our design ??.

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Normal Forms (Guidelines for RD design)

First Normal Form (1NF) Deals with the shape of the

records

A relation is in 1NF if the values of domain is atomic for each attribute.

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First Normal Form: 1NF

Example: R (A, B, C, …)

R ( A B ) R ( A B ) a1 b1, b2 => a1 b1

a1b2

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First Normal Form: 1NF

Example: Person (Name Age Children )

Smith 42 John, Lori, Mark

Person (Name Age Children )Smith 42 JohnSmith 42 LoriSmith 42 Mark

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First Normal Form: 1NF

Example: Student ( Name Birthday )

S1 Feb 2,91S2 March 8,88

Student (Name, D_Birth, M_Birth, Y_Birth)

Note: 2NF and 3NF Deal with the relationship between non-key and key

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Second Normal Form: 2NF

A relation is in 2NF if it is in 1NF and every attribute is Fully dependent on the entire key in this relation.

Fact: 2NF is violated when a non-key is a fact about a subset of a key

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Second Normal Form: 2NF

Example: R(A,B,C,D)

D partially depends on A,B C fully depends on A,B A&B are prime (part of key)

If A is primary key. Is this in 2NF? If A&B is primary key. Is this in 2NF?

A, B ---> C, DA ---> D

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Second Normal Form: 2NF What should we do with a relation which

is not in 2NF?

Example: R(A,B,C,D) A, B ---> C, D A ---> D

R1 (A,B,C) R2(A,D)

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Second Normal Form: 2NF Example: R(Part Warehouse Address Quantity

P1 W1 Frostburg 25

P2 W1 Frostburg 30

P3 W2 Cumberland

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P4 W4 Frostburg 25

P4 W1What is the primary key?

Part, Warehouse ---> QuantityWarehouse ---> Address

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Second Normal Form: 2NF

Problems:1. Repetition of information:

Changing the address W!

2. Unable to present information:Warehouse with no part

So …R1 (Warehouse, Address)R2 (Part, Warehouse, Quantity)

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Second Normal Form: 2NF

Example:

R( Professor,

Student,

Course,

Degree )

P1 S1 C1 Ph.D.

P2 S2 C2 M.S.

P3 S2 C4 M.S.

P4 S3 C4 Pg.D.Professor ---> CourseStudent ---> DegreeProfessor ---> Student

Key? Not in 2NF

R1(Student, Degree)R2(Professor, Course, Student)

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A relation is 3NF if it is in 2NF and every non-key attribute non transitively depends on the Primary Key.

Example: R(A,B,C,D) A, B --->D D ---> C

Fact: 3NF is violated when a non-key is a fact about another non-key

Third Normal Form (3NF):

R1(A,B,D)R2(D,C)

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Third Normal Form (3NF): Example: R(Employee, Dept, Location) Employee ---> Dept

Dept ---> Location

Employee Dept LocationE1 D1 Frostburg

E2 D2 Frostburg

E3 D3 Frostburg

Problems? R1(Employee, Dept)R2(Dept, Location)

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Third Normal Form (3NF): Example: R(A,B,C,D)

A,B ---> C A,C ---> D

So A,B is the Primary Key Not in 3NF

R1(A,B,C) R2(A,C,D)

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Practice:

Check the relations in your video project for 1NF, 2NF and 3NF. If they are not in normal forms, redesign your database model.