DAT602 Database Application Development Lecture 4 Database Design

DAT602 Database Application Development

Lecture 4 Database Design

Database Application Development - Lecture 4

Basic structure of database application• Three ties model

• Database is the foundation of whole system.Generally, we should design database at very beginning.

Database

Application server (Business logic)

Client (User interface)


Analyze Requirement• Requirement analysis is complicated.• For database design you should consider

which kinds of data are necessary for the expecting system?

• The more careful you consider it, the less risk of modifying database you’ll take in the future.


• In this lecture, we’ll use a Mini online shop as a example to demonstrate how to design a simple database.

• Basic requirement:Sellers can put products online.Buyers can view and buy available products.Details of transaction should be kept.


Mini Online shop• How many entities should be involved in this

system?Customers, sellers, products, transaction.

• Create one table for each entity.

Customer Seller Product Transaction

Tables


Design a table• Which data is needed for each table?• What types of these data?• How long of data is appropriate?• Which column should be primary key?


Table design• Which data is needed for each table?

Only cover necessary and close related data.Column Type

Name Char

ID Char

Email Char

Telephone Char

Height Float

Unnecessary


Table design• What types of these data?

Float, integer, char, date, etc..

Different databases have different type systems, but they are similar.

char vs. varcharThe char is a fixed-length character data type, the varchar is a variable-length character data type.


Table design• How long of data is appropriate?

8bit, 32bit, 128bit?

Longer data costs more storage. Consider carefully.

1 Chinese character = 2 byte = 16 bit


Table design• Which column should be chosen as primary

key?Chose the column will never have two same values.Primary key is used to identify different records.


Customer table.

Column Name Type Length(Byte)

UserName char 16

Address char 128

TelephoneNO char 16

UserID char 16

Email char 32

Balance float 16

Primary Key


Transaction table

Column Name Data type Length

TransactionID char 16

Date date 16

BuyerID char 16

SellerID char 16

ItemID char 16

Amount float 16

TotalPrice float 16

Primary Key

Foreign Key

Foreign Key


Relationship between tables

Column Type

TransactionID char

BuyerID char

SellerID char

… …

Column Type

UserID char

UserName char

… …

Column Type

SellerID char

SellerName char

… …

Primary key

Primary key

Primary key

Foreign key

Foreign key


Normalization• Normalization eliminates redundancies and to

ensure consistent dependencies.Simply, normalization refines database design.


Normalization guideline• There must be no repeated fields.• The table cannot contain fields that are not

related to the primary key.• For a multiple keys table, the table should only

contain data related to one entity, and that entity should be described by its primary key.

• The table cannot contain two or more independent multivalued facts about an entity.


• There must be no repeated fields.

Column Type

UserID Char

FullName Char

Surname Char

… …

Fullname and Surname are conflict, remove Surname or keep Surname and use GivenName to replace Fullname.

Column Type

UserID Char

GivenName Char

Surname Char

… …

Customer tableNormalized Customer table


• The table cannot contain fields that are not related to the primary key.

Column Type

UserID Char

UserName Char

TransactionID Char

… …

For customer table, TransactionID is not a part of customer information, but a part of transaction, you should remove it.

Column Type

UserID Char

UserName Char

… …

Customer tableNormalized Customer table


• For a multiple keys table, the table should only contain data related to one entity, and that entity should be described by its primary key.

Column Type

TransactionID Char

BuyerID Char

SellerID Char

BuyerName Char

… …

Primary key

Foreign key

Foreign key

Transaction Table

Column Type

TransactionID Char

BuyerID Char

SellerID Char

… …

Normalized Transaction Table


• The table cannot contain two or more independent multi-valued facts about an entity.

UserID(Primary Key)

Telephone

007 123456

007 345678

008 389207

… …

Customer TableUserID(Primary Key)

Telephone1 Telephone2

007 123456 345678

008 389207 <NULL>

… …

Normalized Customer Table

Primary key can not has two records with same value.


• ViewViews are implemented in a relational database system by allowing the user to select data from the database to create temporary tables, known as views.


TransactionID Date UserID UserName UserTelephone Seller ….

Transaction Customer Seller

View of detailed transaction

Tables


• Keep each table as simple as possible, just assign necessary columns to it, you can create views by combining data from multiple tables.


• Literature“Java Database Programming Bible”,by John O'Donahue ISBN:0764549243John Wiley & Sons © 2002

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DAT602 Database Application Development Lecture 4 Database Design