Database Reference
In-Depth Information
Consider the AGENTS and CLIENTS tables in
Figure 3.17
once more. If you require an
agent to handle
at least one
client, but certainly no more than eight, then the degree of par-
ticipation for the CLIENTS table is
1,8.
When you want to ensure that a client can only be
assigned to one agent, then you indicate the degree of participation for the AGENTS table
as
1,1.
You'll learn how to indicate the degree of participation for a given relationship in
Integrity-Related Terms
Field Specification
A
field specification
(traditionally known as a
domain
)
represents all the elements of a
field. Each field specification incorporates three types of elements:
general, physical,
and
logical.
•
General
elements constitute the most fundamental information about the field and
include items such as Field Name, Description, and Parent Table.
•
Physical
elements determine how a field is built and how it is represented to the
person using it. This category includes items such as Data Type, Length, and Dis-
play Format.
•
Logical
elements describe the values stored in a field and include items such as
Required Value, Range of Values, and Default Value.
You'll learn all of the elements associated with a field specification, including those men-
tioned here, in
Chapter 9
,
“
Field Specifications
.
”
Data Integrity
Data integrity
refers to the validity, consistency, and accuracy of the data in a database. I
cannot overstate the fact that the level of accuracy of the information you retrieve from the
database is in direct proportion to the level of data integrity you impose upon the database.
Data integrity is one of the most important aspects of the database design process, and you
cannot underestimate, overlook, or even partially neglect it. To do so would put you at risk
of being plagued by errors that are very hard to detect or identify. As a result, you would
be making important decisions on information that is inaccurate at best, or totally invalid
at worst.
Therearefourtypesofdataintegrity thatyou'llimplement duringthedatabase designpro-
cess. Three types of data integrity are based on various aspects of the database structure
and are labeled according to the area (level) in which they operate. The fourth type of data
integrity is based on the way an organization perceives and uses its data. The following is
a brief description of each.
