Database Reference
In-Depth Information
Description of information.
The data modeling technique describes real-world
information in terms of entities, their attributes, and the relationships among the
entities.
Graphics and rules.
You draw an entity-relationship diagram (ERD) according to
appropriate rules by using well-defined graphical symbols.
Theoretical foundation.
The modeling technique rests on a solid foundation on the
principles of entities, attributes, and relationships.
Means for communication.
An E-R model proves to be a useful and easily under-
stood means for communication among the IT professionals on the database project
as well as with user representatives.
Data Modeling Process
E-R data modeling seems to be a natural way of looking at real-world information
without being particularly guided by business processes. Following up on this real-
ization, Figure 7-1 illustrates how E-R data modeling derives the components, one
by one, as a result of natural observation of real-world information.
The figure essentially illustrates the process of creating an E-R model.
Carefully note the boxes on the left side of the figure showing how each
observation seems to follow naturally from the previous one. Let us see how
this process of creating an E-R model works from one observation to the next. This
is how the model is created from observations made of the information
requirements.
Consider a typical organization without getting into too much detail. Let us
record the flow of observations and the derivation of the components.
Real-world
Information
E-R Data Model
Components
“Things” important to the organization
ENTITY
“Things” have properties
ATTRIBUTE
Each “thing” must be uniquely identified
KEY
“Things” have associations among them
RELATIONSHIP
CARDINALITY /
OPTIONALITY
“Things” and associations conform to rules
Enhanced E-R Model
GENERALIZATION /
SPECIALIZATION
Some “things” are subsets of other “things”
Figure 7-1
Deriving E-R data model components.
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