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Chapter 5 Database Processing
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metadata as it appears in Microsoft Access. Each row of the top part of this form describes a column
of the Email table. The columns of these descriptions are Field Name, Data Type, and Description. Field
Name contains the name of the column, Data Type shows the type of data the column may hold,
and Description contains notes that explain the source or use of the column. As you can see, there
is one row of metadata for each of the four columns of the Email table: EmailNum, Date, Message,
and Student Number.
The bottom part of this form provides more metadata, which Access calls Field Properties, for
each column. In Figure 5-7, the focus is on the Date column (note the light rectangle drawn around
the Date row). Because the focus is on Date in the top pane, the details in the bottom pane pertain to
the Date column. The Field Properties describe formats, a default value for Access to supply when a
new row is created, and the constraint that a value is required for this column. It is not important
for you to remember these details. Instead, just understand that metadata is data about data and
that such metadata is always a part of a database.
The presence of metadata makes databases much more useful. Because of metadata, no one
needs to guess, remember, or even record what is in the database. To find out what a database
contains, we just look at the metadata inside the database.

Q5-3 What Is a Database Management System (DBMS)?

A database management system (DBMS) is a program used to create, process, and administer
a database. As with operating systems, almost no organization develops its own DBMS. Instead,
companies license DBMS products from vendors such as IBM, Microsoft, Oracle, and others. Popular
DBMS products are DB2 from IBM, Access and SQL Server from Microsoft, and Oracle Database
from the Oracle Corporation. Another popular DBMS is MySQL, an open source DBMS product that
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is license-free for most applications. Other DBMS products are available, but these five process the
great bulk of databases today.
Note that a DBMS and a database are two different things. For some reason, the trade press
and even some books confuse the two. A DBMS is a software program; a database is a collection of
tables, relationships, and metadata. The two are very different concepts.

Creating the Database and Its Structures
Database developers use the DBMS to create tables, relationships, and other structures in the data-
base. The form in Figure 5-7 can be used to define a new table or to modify an existing one. To create
a new table, the developer just fills the new table’s metadata into the form.
To modify an existing table—say, to add a new column—the developer opens the metadata
form for that table and adds a new row of metadata. For example, in Figure 5-8 the developer has
added a new column called Response?. This new column has the data type Yes/No, which means
that the column can contain only one value—Yes or No. The professor will use this column to
indicate whether he has responded to the student’s email. A column can be removed by deleting its
row in this table, though doing so will lose any existing data.

Processing the Database

The second function of the DBMS is to process the database. Such processing can be quite complex,
SQL is essential for processing a but, fundamentally, the DBMS provides applications for four processing operations: to read, insert,
database, but it can be misused by modify, or delete data. These operations are requested in application calls upon the DBMS. From a
criminals to steal data. This kind
of SQL injection attack is described form, when the user enters new or changed data, a computer program behind the form calls the
in the Security Guide on pages DBMS to make the necessary database changes. From a Web application, a program on the client
224–225. or on the server calls the DBMS to make the change.