2 cissp ® Official Study Guide Eighth Edition

897
Relational Databases
A relational database consists of flat two-dimensional tables made up of rows and columns. 
In fact, each table looks similar to a spreadsheet file. The row and column structure pro-
vides for one-to-one data mapping relationships. The main building block of the relational 
database is the table (also known as a 
relation
). Each table contains a set of related records. 
For example, a sales database might contain the following tables:
■
Customers table that contains contact information for all the organization’s clients
■
Sales Reps table that contains identity information on the organization’s sales force
■
Orders table that contains records of orders placed by each customer
object-oriented Programming and Databases
Object-relational databases combine relational databases with the power of object-
oriented programming. True object-oriented databases (OODBs) benefit from ease of 
code reuse, ease of troubleshooting analysis, and reduced overall maintenance. OODBs 
are also better suited than other types of databases for supporting complex applications 
involving multimedia, CAD, video, graphics, and expert systems.
Each table contains a number of attributes, or 
fields
. Each attribute corresponds to a 
column in the table. For example, the Customers table might contain columns for company 
name, address, city, state, zip code, and telephone number. Each customer would have its 
own record, or 
tuple
, represented by a row in the table. The number of rows in the rela-
tion is referred to as 
cardinality
, and the number of columns is the 
degree
. The 
domain
of 
an attribute is the set of allowable values that the attribute can take. Figure 20.8 shows an 
example of a Customers table from a relational database.
F I g u r e 2 0 . 8
Customers table from a relational database
1
2
3
234 Main Street
1024 Sample Street
913 Sorin Street
MD
FL
IN
21040
33131
46556
[phone]
[phone]
[phone]
14
14
26
Columbia
Miami
South Bend
Acme Widgets
Abrams Consulting
Dome Widgets
Company ID
Address
State
ZIP Code
Telephone
Sales Rep
City
Company Name
In this example, the table has a cardinality of 3 (corresponding to the three rows in the 
table) and a degree of 8 (corresponding to the eight columns). It’s common for the cardi-
nality of a table to change during the course of normal business, such as when a sales rep 
adds new customers. The degree of a table normally does not change frequently and usually 
requires database administrator intervention.

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898
Chapter 20 
■
Software Development Security
To remember the concept of cardinality, think of a deck of cards on a desk, 
with each card (the first four letters of
cardinality
) being a row. To remem-
ber the concept of degree, think of a wall thermometer as a column (in 
other words, the temperature in degrees as measured on a thermometer).
Relationships between the tables are defi ned to identify related records. In this example, 
a relationship exists between the Customers table and the Sales Reps table because each 
customer is assigned a sales representative and each sales representative is assigned to 
one or more customers. This relationship is refl ected by the Sales Rep fi eld/column in the 
Customers table, shown in Figure 20.8 . The values in this column refer to a Sales Rep 
ID fi eld contained in the Sales Rep table (not shown). Additionally, a relationship would 
probably exist between the Customers table and the Orders table because each order must 
be associated with a customer and each customer is associated with one or more product 
orders. The Orders table (not shown) would likely contain a Customer fi eld that contained 
one of the Customer ID values shown in Figure 20.8 . 
Records are identifi ed using a variety of keys. Quite simply,
keys
are a subset of the fi elds 
of a table and are used to uniquely identify records. They are also used to join tables when 
you wish to cross-reference information. You should be familiar with three types of keys: