Introduction - Database Processing: Fundamentals, Design, and Implementation - page 11

report that displays all the Student-Class-Grade data shown in Figure 1-3 sorted by ClassNumber
and LastName. Notice that the report, like the form in Figure 1-9, is structured according to the
users' needs, not according to the underlying table structure.
In addition to generating forms, queries, and reports, the application program takes other
actions to update the database in accordance with application-specific logic. For example,
suppose a user using an order entry application requests 10 units of a particular item. Suppose
further that when the application program queries the database (via the DBMS), it finds that
only 8 units are in stock. What should happen? It depends on the logic of that particular appli-
cation. Perhaps no units should be removed from inventory and the user should be notified, or
perhaps the 8 units should be removed and 2 more placed on back order. Perhaps some other
action should be taken. Whatever the case, it is the job of the application program to execute
the appropriate logic.
Finally, the last function for application programs listed in Figure 1-8 is to control the
application. This is done in two ways. First, the application needs to be written so that only
logical options are presented to the user. For example, the application may generate a menu
with user choices. In this case, the application needs to ensure that only appropriate choices
are available. Second, the application needs to control data activities with the DBMS. The ap-
plication might direct the DBMS, for example, to make a certain set of data changes as a unit.
The application might tell the DBMS to either make all these changes or none of them. You will
learn about such control topics in Chapter 9.

The DBMS
The DBMS, or database management system, creates, processes, and administers the data-
base. A DBMS is a large, complicated product that is almost always licensed from a software
vendor. One DBMS product is Microsoft Access. Other commercial DBMS products are Oracle
Database and MySQL, both from Oracle Corporation; SQL Server, from Microsoft; and DB2,
from IBM. Dozens of other DBMS products exist, but these five have the lion's share of the
market. Figure 1-12 lists the functions of a DBMS.
A DBMS is used to create a database and to create the tables and other support-
ing structures inside that database. As an example of the latter, suppose that we have an
EMPLOYEE table with 10,000 rows and that this table includes a column, DepartmentName,
that records the name of the department in which an employee works. Furthermore, sup-
pose that we frequently need to access employee data by DepartmentName. Because this

Figure 1-12
Functions of a DBMS

Functions of a DBMS

Create database

Create tables

Create supporting structures (e.g., indexes)

Modify (insert, update, or delete) database data

Read database data

Maintain database structures

Enforce rules

Control concurrency

Perform backup and recovery