Database Systems and Business Intelligence - Principles of Information Systems - page 184

Hierarchy of data Example

Figure 5.1

The Hierarchy of Data

Database

Personnel file
Department file
Payroll file

(Project database)

098 - 40 - 1370 Fiske, Steven 01-05-1985
549 - 77 - 1001 Buckley, Bill 02-17-1979
005 - 10 - 6321 Johns, Francine 10-07-1997

Files

(Personnel file)

(Record containing
SSN, last and first
name, hire date)

Records

098 - 40 - 1370 Fiske, Steven 01-05-1985

Fields

(Last name field)

Fiske

Characters
(bytes)

(Letter F in ASCII)

1000110

An attribute is a characteristic of an entity. For example, employee number, last name,
first name, hire date, and department number are attributes for an employee (see Figure 5.2).
The inventory number, description, number of units on hand, and location of the inventory
item in the warehouse are attributes for items in inventory. Customer number, name, address,
phone number, credit rating, and contact person are attributes for customers. Attributes are
usually selected to reflect the relevant characteristics of entities such as employees or cus-
tomers. The specific value of an attribute, called a data item , can be found in the fields of
the record describing an entity.

attribute
A characteristic of an entity.

data item
The specific value of an attribute.

Figure 5.2

Employee # Last name First name Hire date Dept. number

Keys and Attributes
The key field is the employee
number. The attributes include last
name, first name, hire date, and
department number.

Johns Francine 10-07-1997 257

005-10-6321

Bill 632

549-77-1001 Buckley 02-17-1979

098-40-1370 Fiske Steven 01-05-1985 598

KEY FIELD

ATTRIBUTES (fields)

Most organizations use attributes and data items. Many governments use attributes
and data items to help in criminal investigations. The United States Federal Bureau of
Investigation is building the “world's largest computer database of peoples' physical
characteristics.” 7 At a cost of $1 billion, the database management system named Next
Generation Identification will catalog digital images of faces, fingerprints, and palm prints
of U.S. citizens and visitors. Each person in the database is an entity, each biometric category
is an attribute, and each image is a data item. The information will be used as a forensics tool
and to increase homeland security.
As discussed, a collection of fields about a specific object is a record. A key is a field or
set of fields in a record that identifies the record. A primary key is a field or set of fields that
uniquely identifies the record. No other record can have the same primary key. The primary
key is used to distinguish records so that they can be accessed, organized, and manipulated.
For an employee record, such as the one shown in Figure 5.2, the employee number is an
example of a primary key.

key
A field or set of fields in a record that
is used to identify the record.
primary key
A field or set of fields that uniquely
identifies the record.