Database Management Systems
Getting Data Together
Appreciate the advantages of databases
Understand how databases are organized
Become familiar with database terminology
Understand, in general, how to build and change a database
Students will get the most out of this chapter if it is accompanied by hands-on experience, using
database software on a personal computer. However, if hands-on is not available, a student should still
be able to understanding the power and usefulness of databases, and also have some notion of what it
takes to put one together.
 Getting It Together: Database Systems
A database is an organized collection of related data.
A database management system (DBMS) is software that helps organize data in a way that
allows fast and easy access to the data.
With a database program a user can create, modify, store, and retrieve data in a variety of ways.
Databases Are Different
Database systems are different from word processing or spreadsheet software, in which users
enter and use the data in the same form as it resides on disk.
Data in databases could reside on the disk in ways unknown to a user. In particular,
sophisticated database systems, particularly those designed for a mainframe computer
environment, are complex, and must be planned and managed by computer professionals.
Users of such systems are trained to input data to and retrieve data from the database system,
using appropriate software; they can do this successfully without ever having to understanding
the underlying technology.
On the other hand, database software is available for personal computers that a trained user can
apply to simple or moderately complex problems.
Advantages of Databases
Several advantages are generally associated with databases.
Reduced redundancy. Data carried in separate files, as opposed to a database, tends to
repeat some of the same data over and over. In a database, information generally appears
just once.
Integrated data. Rather than being in separate and independent files, data in a database is
considered integrated because any item of data can be used to satisfy an inquiry or a report.
Integrity. Integrity concerns increase as the sophistication of the data increases. Reduced
redundancy increases the likelihood of data integrity.
 Database Concepts
In this chapter we will look at database management in a generic way, without reference to any
specific package.
Database Models
The way the database organizes data depends on the type, or model, of the database.
There are three database models—hierarchical, network, and relational. Databases on personal
computers are usually relational.
A relational database organizes data in a table format consisting of related rows and columns.
In a relational system, data in one file can be related to data in another, allowing you to tie together
data from several files.
Fields, Records, and Files
In a relational database a table is called a relation. A relation is also called a file.
Each box in the table contains a piece of data, known as a data item.
Each column of the table represents a field. The specific data items in a field may vary, but each
field contains the same type of data.
All the data in any given row is called a record.
Each record has a fixed number of fields, but there can be a variable number of records in a given
Database Power
The power of a database is in the connection: a relational system can relate data in one file to
data in another file, allowing a user to tie together data from several files.
(At this point, the easiest approach is to follow the example in the text; the figures should help.)
A Problem Fit For a Database
(Again, at this point, the problem is best followed from the text.)
 Creating and Using a Database
There are two steps to creating a database file: designing the structure of the file and entering the
data into the file.
Determining the File Structure
The file structure is a description of what data is wanted in each column.
To create the file structure, a user must choose meaningful fields, based on the data to be retrieved
from the database.
Field Name
Names of the types of data to be used are called field names.
A field name must be unique.
Field Type
There are four commonly used types of fields:
Character fields contain descriptive data such as names, addresses, and telephone numbers.
Numeric fields contain numbers used for calculations. You must specify the number of
decimal places you wish to use.
Date fields are automatically limited to eight characters, including the slashes used to separate
the month, day, and year.
Logical fields keep track of true and false conditions.
Field Widths
The field width determines the maximum number of characters or digits to be contained in the
field, including decimal points.
Key Fields
One or more key fields can be designated as a field on which an inquiry to the database can be
A key field is sometimes called an index field.
Setting Up the File Structure
Although different database packages may take different approaches, in Microsoft Access, used
to demonstrate the example in the text, the design view is set up like a table, with one line per
database field.
Entering the Data
Once a database structure is established, the data can be entered.
(If you wish to follow the example, details are in the text.)
Other Options
The following are descriptions of operations that would be available with any database software
List the records
A user could ask for a list of all existing records, either displayed on the screen or printed out on
paper. The software displays as many records as will fit on the screen.
Scrolling up or down displays additional records. If there were a large number of fields in a
record, a user could pan—move horizontally across the screen—to the left or right.
List specific fields
In addition to printing all records, a user has the option of printing just certain fields of each
A user can make a query—ask a question—about the records in the file, using a relational
operator when entering instructions that involve making comparisons. (See Table 11-1 in the
text for details of relational operators.)
Add new records
A user can add records at any time.
Modify existing records
A user may change data in an existing record.
Delete records
A user may remove—delete—a record from a database file.
character field
data item
database management system
date field
field name
field type
field width
file structure
integrated data
key field
logical field
numeric field
reduced redundancy
relational database
relational operator