Nuevas Tarea

Database Management

which sales representative deserves the award
for highest annual sales if the December sales
have not yet been placed in the database.
• Useful information has meaning to the person
who receives it. Most information is important
only to certain people or groups of people.
Always consider the audience when collecting and reporting information. Avoid distributinguseless information. For example, an
announcement of an alumni association meeting
is not useful to students not yet graduated.
• Cost-effective information should give more
value than it costs to produce. An organization
occasionally should review the information it
produces to determine if it still is cost-effective
to produce. Sometimes, it is not easy to place
a value on information. Forthis reason, some
organizations create information only on
demand, that is, as people request it, instead
of on a regular basis. Many make information
available online. Users then can access and
print online information as they need it. For
example, sending a printed benefits manual to
each employee could be quite costly. Instead,
employees can access an online benefits
manual, when theyneed to review it.

database files
stored on disk

SCHOOL DATABASE

Student File
Instructor File

517

FAQ 10-1

How can I verify the accuracy of my credit report?
The three credit reporting agencies (Equifax, Experian, and TransUnion) developed
a central Web site at annualcreditreport.com. Through this Web site, you can
request a free copy of your credit report from each creditreporting agency every
12 months. You also can request the reports by mailing a form or calling a toll-free
number. If you would like constant monitoring of the activity on your credit report,
you can subscribe to a credit monitoring service for a minimal fee. The service will
contact you if any unusual or suspicious activity occurs on your credit report.
For more information, visitscsite.com/dc2011/ch10/faq and then click
Verifying Credit Report Accuracy.

The Hierarchy of Data
Data is organized in layers. In the computer
profession, data is classified in a hierarchy. Each
higher level of data consists of one or more
items from the lower level. For example, a student has an address, and an address consists of
letters and numbers. Depending on the application and the user,different terms describe the
various levels of the hierarchy.
As shown in Figure 10-2, a database contains
files (sometimes called tables), a file contains
records, a record contains fields, and a field is
made up of one or more characters. This sample
School database contains four files: Student,
Instructor, Schedule of Classes, and Student
Schedule. The Student file contains records aboutenrolled students. The Instructor file contains
records about current instructors. The Schedule of
Classes file contains records about class offerings
in a particular semester, and the Student Schedule
file contains records about the classes in which a
student is enrolled for a given semester. Each field
in a record contains many characteristics, one of
which is the field size.

Schedule ofClasses File
Student Schedule File

Characteristics of Instructor ID Field
field names

Instructor File

records

fields

Figure 10-2

Chapter 10

A sample school database with four files: Student, Instructor, Schedule of Classes, and
Student Schedule. The sample Instructor file contains four records. Each record contains six fields. The
Instructor ID field can contain a maximumof six characters (bytes).

maximum
characters in
Instructor ID
field

5 18

Chapter 10

D atabase Management

Characters
As discussed in Chapter 4, a bit is the smallest
unit of data the computer can process. Eight bits
grouped together in a unit comprise a byte. In
the ASCII coding scheme, each byte represents a
single character, which can be a number (4), letter
(R),...