Microsoft Office Tutorials and References
In Depth Information
Session 1.1
When you include the primary key from one table as a field in a second table to form a
relationship between the two tables, it is called a foreign key in the second table, as
shown in Figure 1-2. For example, EmployerID is the primary key in the Employer table
and a foreign key in the Position table. Although the primary key EmployerID has unique
values in the Employer table, the same field as a foreign key in the Position table does not
necessarily have unique values. The EmployerID value 10126, for example, appears three
times in the Position table because the BaySide Inn & Country Club has three available
positions. Each foreign key value, however, must match one of the field values for the pri-
mary key in the other table. In the example shown in Figure 1-2, each EmployerID value
in the Position table must match an EmployerID value in the Employer table. The two
tables are related, enabling users to connect the facts about employers with the facts
about their employment positions.
Relational Database Management Systems
To manage its databases, a company purchases a database management system. A
database management system (DBMS) is a software program that lets you create data-
bases and then manipulate data in them. Most of today’s database management systems,
including Access, are called relational database management systems. In a relational
database management system , data is organized as a collection of tables. As stated earlier,
a relationship between two tables in a relational DBMS is formed through a common field.
A relational DBMS controls the storage of databases on disk and facilitates the creation,
manipulation, and reporting of data, as illustrated in Figure 1-3. Specifically, a relational
DBMS provides the following functions:
• It allows you to create database structures containing fields, tables, and table
relationships.
• It lets you easily add new records, change field values in existing records, and delete
records.
• It contains a built-in query language, which lets you obtain immediate answers to the
questions you ask about your data.
• It contains a built-in report generator, which lets you produce professional-looking,
formatted reports from your data.
• It protects databases through security, control, and recovery facilities.
Figure 1-3
Relational database management system
disk storage
database
store, retrieve, and protect data
computer memory
relational DBMS
query
displays
hard copy
reports
user
interaction
with the
database
printer
users
 
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