Database Design

J.G. ZhengJune 29th 2005

DB Chapter 5

2

Overview

Entity Relationship Modeling Data modeling using Entity

Relationship Diagram (ERD)

Transforming ERD into tables

3

Introduction/Review

Design is a process Analysis

Requirements (user view) Conceptual modeling (ERD)

(Logical) design Transforming ERD to tables and keys

Physical design and implementation Using MS Access

4

Entity-Relationship Model

A model to represent the real world

Elements Entities Attributes Identifiers Relationships

For ER Model, refer to the book on page 419-423

5

Entity

Entity Anything in the real world

Entity class (entity set) A set of things of the same type

Entity instance An exact instance of an entity class

ERD notation for entity A rectangular box

Books

6

Attribute and Identifier

Attribute Properties of entity Notation: an oval

Identifier An attribute with unique value to identify each instance

Title

Books

ISBN

Price

7

Relationship

Notation: a diamond

Degree of relationship Unary (recursive) – only 1 entity Binary – 2 entities Ternary – 3 entities N-ary – more entities

Books Publisherspublish

8

Types of Binary Relationship

One-to-One (1:1) A single entity instance in one entity class is

related to a single entity instance in another entity class

Examples: Governors : States Students : PantherCards

ER Notation (Crow’s foot)

Governors Statesgovern

9

Types of Binary Relationship

One-to-Many (1:N) A single entity instance in one entity class

(parent) is related to multiple entity instances in another entity class (child)

Examples Customers : Orders Students : Degrees

ER Notation (Crow’s foot)

Books Publisherspublish

10

Types of Binary Relationship

Many-to-Many (N:M) Each entity instance in one entity class is

related to multiple entity instances in another entity class; and vice versa

Examples Books : Writers Customers : Banking Accounts

ER Notation (Crow’s foot)

Books Authorswrite

11

CardinalityCardinality Describes participation in the relationship Figure 5.43 on page 423

Maximum cardinalities (types of relationships)

Minimum cardinalities Optional (zero) or Mandatory (one)

Certificates Programmershave

12

A Complete ER Example

13

ER Diagram ExerciseDraw a ERD about movie data

Let’s only consider the following entities and their attributes

Perfomers: PerformerID, FirstName, LastName, Gender

Movies: MovieID, Title, Maker, Year MovieMakers(companies): MakerID, Name

Assumptions A movie has at least one actor/actress An actor/actress does not have to be in any movie A movie is made by only one company

14

Transforming ER to Tables

Guidelines to create tables Each entity becomes a relation (table) Attributes of the entity become fields of that

table Identifier becomes primary key

Rules to transform relationships Based on the type of the relationship

One-to-One One-to-Many Many-to-Many

15

Transforming 1:1 Relationships

One-to-One The key from one relation is placed in

the other as a foreign key

LockerDesc

Location

LockerID

Locker

LockerID

EmpName

EmpID

Employee

Foreign Key

Primary Key

16

Transforming 1:1 Relationships

EmpID

LockerDesc

Location

LockerID

Locker

EmpName

EmpID

Employee

Foreign Key

Primary Key

Usually, it does not matter which table receives the foreign key

17

Transforming 1:N Relationships

One-to-Many The primary key from the “One” side is placed

in the “Many” side as a foreign key The foreign key is always on the “Many” side

Instructor

InstructorID

FirstName

Office

Department

CourseSection

CRN

Semester

CourseID

Time

TaughtBy

18

Transforming 1:N Relationships

Another example

DeptName

Location

DeptID

Department

Dept

EmpName

EmpID

Employee

Foreign Key

Primary Key

Department Employeehas

19

Transforming N:M Relationships

Many-to-Many There is no direct way to map many

to many relationships To represent an M:N relationship, a

table is created (intersection table) for the relationship

Orders PartsOrderItems

20

Transforming N:M Example

Many-to-Many is designed as two One-to-Many relationships

Create an intersection table with the primary key from each original table as foreign keys

The intersection table usually has a composite primary key

OrderItems

OrderNum

PartNum

NumOrdered

Orders

OrderNum

OrderDate

CustomerNum

Parts

PartNum

Description

Class

Price

1:N

N:1

21

M:N Relationship Exercise

Performers MoviesCast

PerformerId

FirstName

LastName

Length

Title

Character

MovieId

Gender

22

Database Design Language (DBDL)

Customers (CustomerID, FirstName, LastName, Address, SSN, …)

AK SSN

Orders (OrderNumber, OrderDate, Orderby, ShippingMethod, …)

FK Orderby Customers

23

IDEF1X

Understand Figure 5.2 on page 384

24

Review QuestionGiven the entities SUPPLIER and PRODUCT are one-to-many relationship, which of the following would represent the correct table design?

A. PRODUCT (ProductID, Description, Cost)SUPPLIER (SupplierID, ContactName, PhoneNumber)

FK ProductID PRODUCT

B. PRODUCT (ProductID, Description, Cost, SupplierID)FK SupplierID SUPPLIER

SUPPLIER (SupplierID, ContactName, PhoneNumber, ProductID)FK ProductID PRODUCT

C. PRODUCT (ProductID, Description, Cost, ContactName) FK ContactName SUPPLIER SUPPLIER (SupplierID, ContactName, PhoneNumber)

D. PRODUCT (ProductID, Description, Cost, SupplierID)FK SupplierID SUPPLIER

SUPPLIER (SupplierID, ContactName, PhoneNumber)

25

Summary

E-R diagram is used widely for database design

Remember the rules to transform ERD to actual tables and relationships One to one One to many Many to many