Page 200 -

Q5-2 What Is a Database?

%QNWOPU CNUQ ECNNGF HKGNFU 199

5VWFGPV 0WODGT 5VWFGPV 0COG *9 *9 /KF6GTO
$#-'4 #0&4'#
.#7 59''
0'.510 567#46
4QYU
CNUQ ECNNGF (+5%*'4 /#;#0
TGEQTFU 6#/ ,'((4';

8'4$'44# #&#/
8#.&'< /#4+'
41)'45 5*'..;
Figure 5-3
Student Table (also called a file) %JCTCEVGTU CNUQ ECNNGF D[VGU

Q5-2 What Is a Database?

A database is a self-describing collection of integrated records. To understand the terms in this defi-
nition, you first need to understand the terms illustrated in Figure 5-3. As you learned in Chapter 4,
a byte is a character of data. In databases, bytes are grouped into columns, such as Student Number
and Student Name. Columns are also called fields. Columns or fields, in turn, are grouped into rows,
which are also called records. In Figure 5-3, the collection of data for all columns (Student Number,
Student Name, HW1, HW2, and MidTerm) is called a row or a record. Finally, a group of similar rows
or records is called a table or a file. From these definitions, you can see a hierarchy of data elements,
as shown in Figure 5-4.
It is tempting to continue this grouping process by saying that a database is a group of tables
or files. This statement, although true, does not go far enough. As shown in Figure 5-5, a database
is a collection of tables plus relationships among the rows in those tables, plus special data, called
metadata, that describes the structure of the database. By the way, the cylindrical symbol labeled
“database” in Figure 5-5 represents a computer disk drive. It is used like this because databases are
most frequently stored on disks.

6CDNG QT (KNG 5VWFGPV 0WODGT 5VWFGPV 0COG *9 e
5VWFGPV 0WODGT 5VWFGPV 0COG *9 e
5VWFGPV 0WODGT 5VWFGPV 0COG *9 e
5VWFGPV 0WODGT 5VWFGPV 0COG *9 e
5VWFGPV 0WODGT 5VWFGPV 0COG *9 e

)TQWR QH

4GEQTFU QT 4QYU 5VWFGPV 0WODGT 5VWFGPV 0COG *9 e
e
)TQWR QH

(KGNFU QT %QNWOPU 5VWFGPV 0WODGT 5VWFGPV 0COG *9
e
)TQWR QH
Figure 5-4 $[VGU QT %JCTCEVGTU $ # - ' 4
Hierarchy of Data Elements e