1. Database Management Systems
Session 5

2. Objectives Understand the structure of a data table
Understand data normalisation
Understand and use the terms: - entity - attribute - field - record - primary key
Understand the principle of linking tables in a relational database

3. Topics
Database Tables
Normalisation
Linking Tables
Database Schema

4. Address Book Name Address Tel FAX Mobile Email Gertrude Jones
34 Great West Road London
W23 8RT
Record
Field
Data

5. Contacts Table Field Record Name Address Phone FAX Mobile Email
Darren Adamson
6 Spring Gardens
Gertie Jones
34 Great West Road, London W23 8RT
Cedric Jones
Jessie Wallace
18 Loch Arber Crescent, Edinburgh EH8 9OP
Field
Record

6. Entities and Attributes
“I want to record the names and addresses of my contacts along with their phone numbers, FAX numbers, mobile numbers and their addresses”
Entity: Contact
Attributes of Contact: - Name - Address - Phone - FAX - Mobile -

7. Ordered Collection of Data
Characteristics: - each Record is unique - repetition of data is avoided
Database Tables follow certain rules called: - First Normal Form - Second Normal Form - Third Normal Form

8. Primary Key
A Field (or fields) which has a unique value for each record
Eg. - National Insurance number - Car registration number - Passport number

9. First Normal Form Data is atomic, self-contained and independent
No field in a table contains any repeating groups
No record in a table contains repeating groups

10. Second Normal Form
All the non-key columns must be dependent on the entire primary key

11. Third Normal Form
All the non-key columns of the table must be only dependent on the primary key and not on each other

12. Identifying Entities and Relationships
Read the scenario and pick out the nouns
Pick out which nouns are giving information about another noun eg Name is telling you additional information about Contact
In this case Contact is the Entity and Name is an Attribute of that Entity

13. Exercise: Entities and Attributes
Pick out the database entities and suggest useful attributes:
A library has about 300 borrowers who complete a registration form when they join. There are about 25,000 books available for loan. A loan is for 2 weeks and may be renewed over the phone. Overdue books are charged at 10p per day. If a book is out on loan, another borrower may request it.

14. Text Data For example the Name field
The size of the field is determined by the maximum number of characters you want to store
The size of the field is the same for each record so empty spaces waste storage space

15. Number Data For Example in the Salary field
The size of the field is determined by the maximum precision of the numbers you want to store
Integer
Long Integer
Single
Double

16. Date Data Stored on the computer as a number
Different Formats eg: Short date – 01/02/06

17. Logical Data Otherwise known as ‘Yes/No’
Takes up minimal storage space

18. Sorting on Text Data Yellow 22 3 Apple A plum 22 3 A plum Apple Yellow
Sort Ascending

19. Points to Consider What type of data is a telephone number?
How can you name files on a Windows system with digits so that they sort correctly?

20. Linking on the Primary Key
Customer
Customer ID
Name
Address
Phone
Credit Limit
Purchase
Purchase ID
Date
Item
Amount PK

21. Linked Fields Linked Fields One to Many Relationship Purchases
Purchase ID
Customer ID
Item
1789 3
Fig Rolls
1790 2
Arabiata Sauce
1791
Black Olives
1792
Porcini Mushrooms
1793 5
Smoked Salmon
1794 4
Cod Roe
1795 1
Cured Ham
1796
Sugar Snap Peas
1797
Ginger Beer
1798
Ground Cumin
Customers
Customer ID
Name 1
Felipe Martins 2
Tom Smith 3
Kimberley Brown 4
Steve Hammer 5
Alfred Futterkist
One to Many Relationship

22. Most Common Types of Relationship
Staff
Purchase
Customer
Employee
Contractor
One to Many Where one record in one table links with many in the other table
One to One Where one record in one table links with one in the other table

23. Many to Many Relationship
Borrower
Book
Many to Many Link A borrower can borrow many books and a book may be borrowed by many borrowers – over a period of time

24. Resolving Many to Many Relationships
Many to Many Links are impossible to programme into a database system. This type of relationship may be resolved into 2 many to one relationships.
Book
Borrower
Loan

25. Scenario Draw an E-R diagram:
Northwind is a wholesaler of delicatessen products. Customers are all over the world and each member of the sales team may deal with any customer. Products is kept in a central warehouse and items are ordered from Suppliers when numbers reach the re-order level. An Order may consist of several different products and may be delivered by any one of three Shippers.

26. Entity-Relationship Diagram