DATA MODELING BASICS - Database Design and Development: An Essential Guide for IT Professionals - page 152

First, let us consider the object-based modeling technique. In a real-world situa-
tion, every organization deals with business objects. You may even say that the orga-
nization's business processes are mere involvement with business objects. In the case
of a university, the business objects include STUDENT, PROFESSOR, CLASS,
COURSE, REGISTRATION, ASSIGNMENT, TEXTBOOK, and so on. For an
airline business, the business objects include PASSENGER, AIRCRAFT,

RESERVATION, ROUTE, MANUFACTURER, AIRPORT, AIRPLANE,

FLIGHT, and so on.
Object-based modeling technique recognizes and builds on the fact that business
processes involve such business objects. It rests on the premise that if your model
reflects relevant information about business objects and how they interact with one
another, then the model will truly represent the information requirements. There-
fore, by adopting the object-based modeling technique, you produce a generic data
model composed of the following:

• Business objects
• Characteristics of each object
• Interaction or linkage between pairs of objects
• Number of occurrences in linked pairs
• Method for identifying each unique occurrence of an object
• Special types of object sets
• Linkages within object sets

Entity-Relationship Modeling Technique

The entity-relationship modeling technique is similar to the object-based modeling
technique and produces similar results. The main difference is that the two tech-
niques were developed independently for the same purpose. Their evolutions take
separate paths. In the object-based modeling technique, representation of informa-
tion content is centered upon the concept of business objects. Here, in the entity-
relationship (E-R) modeling technique, as the name of the technique explicitly
indicates, the replica of information requirements is based on business entities and
their relationships.
What are called entities in the E-R modeling technique are the objects in the
object-based technique. However, a few subtle differences exist. The object-based
technique recognizes special types of object sets called supersets and subsets. We
will describe these in Chapter 6. The E-R modeling technique had to be enhanced
later to include such entity sets. On the other hand, the E-R modeling technique
includes concepts such as weak entities. The E-R model technique, more widely
used, is built with well-defined and accepted graphics.
By adopting the entity-relationship modeling technique, you can create a generic
data model consisting of the following:

• Business entities
• Properties of each entity type
• Relationship between pairs of entities