Chapter 11: Databases Learning objectives By the end of this chapter you should be able to

Order no:
07845
Customer no:
056
Sales rep no:
Product
no
Description
Quantity
Price /
unit
Total Price
Total
Customer name:
Address:
Sales Rep name:
CUP
327
563
Laser toner
24
$25
$720
$125
$835
$30
5
Inkjet cartridges
Cambridge square
Cambridge
Date:
25-06-2016
2
Dylan Stoddart
Figure 11.11 An order form
Repeating group: a set of attributes that have more than one set of values when the other attributes each 
have a single value
KEY TERM
167
Part 1: Chapter 11: Databases

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11.06 The Database Management System (DBMS) 
The database approach
It is vital to understand that a database is not just a collection of data. A database is an 
implementation according to the rules of a theoretical model. The basic concept was 
proposed some 40 years ago by ANSI (American National Standards Institute) in its three-
level model. The three levels are:
• the external level
• the conceptual level
• the internal level.
The architecture is illustrated in Figure 11.12 in the context of a database to be set up for our 
theatrical agency.
Figure 11.12 The ANSI three-level architecture for the theatrical agency database
External level
Physical storage
Internal level 
Conceptual level
Finance
view 
Recruitment
view
Program Program
Program Program
Program Program
Publicity
view 
Contract
view
Program
The physical storage of the data is represented here as being on disk. The details of the 
storage (the internal schema) are known only at the internal level, the lowest level in the ANSI 
architecture. This is controlled by the