ENTITY-RELATIONSHIP DATA MODEL - Database Design and Development: An Essential Guide for IT Professionals - page 204

These are basically the same for both modeling techniques. We will therefore con-
centrate on presenting the various components and their notations used to draw the
E-R data model diagram. Because the two data modeling methods were developed
independently, the notations or symbols used for the components are somewhat dif-
ferent. However even in the notations, you will note many resemblances.
Study this chapter for the purpose of reinforcing the concepts already learned in
the discussion of object-based data modeling. Note the variations in certain notions.
Also, observe how the E-R data model includes additional notations to represent
individual types within a particular component.
INTRODUCTION TO E-R MODEL
First of all, note that the E-R data model is another generic model similar to the
object-based data model. You will recall how a generic model is free from the
rules and restrictions of conventional models such as hierarchical, network, and
relational models. As you know, these conventional models call for information
requirements to be perceived in certain given ways and their relationships to be
established according to defined conventions. Being a generic model, the E-R data
model can apply to all types of nuances in information requirements. Again, because
it is a generic data model, the E-R model is amenable to being transformed to any
particular conventional model based on the implementation of your database
system.
The E-R data modeling technique is a widely used method. You have a choice
of many data modeling tools to create the model. Because of its popularity and
widespread use, the notations and symbols are more standardized. This modeling
technique provides a wider range of notations to represent variations within each
component.
Basic Concepts
By way of introduction to the basic concepts and principles of E-R modeling tech-
nique, note the following points:
Mainstream approach. Most data modelers and practitioners seem to prefer the
E-R modeling technique, probably because of the availability of several CASE tools
to support the technique.
Things and associations. Examining any set of information requirements, you
discover that these are really about things and their associations—things that are of
interest to the business and associations that are relevant to the business processes.
The E-R modeling technique recognizes this underlying premise.
Entities and relationships. As the name of the technique signifies, the entity-
relationship modeling technique focuses on entities and relationships as natural
concepts. Entities are the things the business is interested in, and relationships are
the associations among the things.