OBJECT-BASED DATA MODEL: PRINCIPLES AND COMPONENTS - Database Design and Development: An Essential Guide for IT Professionals - page 176

By carefully going through the requirements definition, you will discern the rel-
evant real-world information tied to people, places, materials, events, and concepts.
As mentioned above, information requirements for each process tend to be grouped
in terms of the relevant things. Initially, note all such things with which the business
processes are concerned.
Let us quickly do this exercise for a department store. From the information
requirements, you will recognize the things or objects for the business. The store
buys and sells products; PRODUCT therefore, is a relevant business object. The
store sells products to customers; CUSTOMER becomes a relevant object. The
store invoices customers for the products sold; therefore, INVOICE is a relevant
object. As you continue the inspection of the information requirements for the
department store, one by one, you will recognize all the objects for the business and
come up with a complete list.
Occasionally, you may run into a situation in which it may not be clear whether
a data element must be recognized as a business object to be shown distinctly in the
model or must be indicated as just an attribute of another object. For example, in
the case of the data model for the department store, consider the data element
product line. Each product is part of a product line. The question arises: Should
product line be considered as an attribute of the object PRODUCT or be repre-
sented as a separate object PRODUCT LINE? If the information requirements
demand that the characteristics of product line such as line description, date of intro-
duction of product line, and so on be shown in the model, then product line must
be represented as a distinct object. If the information content dictates that only the
name of the product line be known, then product line becomes an attribute of the
object PRODUCT.
Attributes
Every business object possesses certain properties or characteristics that are rele-
vant to the information requirements. These characteristics describe the various
instances of an object set. For example, last name McKeown describes an instance
of the object EMPLOYEE. Similarly, if that employee was hired on 10/1/1985, hire
date is another attribute describing that instance of the object.
Figure 6-4 shows the attributes of an object STUDENT. Note the names of the
attributes written inside the ellipses or ovals. Observe how these are characteristics
or descriptors of the individual instances of the object set.
So, what are attributes? Attributes of an object are characteristics, properties, or
descriptors. Let us explore the meaning and significance of attributes further.
Inherent Characteristics Consider the data elements StudentID, StudentName,
SocSecNo, StudentPhone, StudentMajor. These data elements are associated with
the object STUDENT. They are innate, natural, or inherent properties of
STUDENT. Next, think of a particular course for which a student has enrolled.
CourseNo is also a data element associated with the object STUDENT. If so, is
CourseNo also an attribute of the object STUDENT? Compare the two data ele-
ments StudentName and CourseNo. StudentName is a natural characteristic of the
object STUDENT, whereas CourseNo does not indicate a basic property of the
object. CourseNo does not describe some intrinsic property of STUDENT but only