Database Reference
In-Depth Information
Balance
AccountNo
has
ACCOUNT
CUSTOMER
*
*
InterestRate
ISA
OverdraftAmt
SAVINGS
ACCOUNT
CHECKING
ACCOUNT
DateOfBirth
ISA
STANDARD
PREMIUM
GOLD
MinPymnt
NumOfChecks
InterestPymnt
Figure 7-20
E-R model: generalization and specialization.
THE ENTITY-RELATIONSHIP DIAGRAM
This section pulls together everything we have covered on E-R data modeling and
summarizes the topic with a comprehensive entity relationship diagram (ERD).
Before we review the diagram and note the components, let us revisit the compo-
nents and their notations. As mentioned above, in practice, you will observe some
minor variations in the notations used by different data modelers. Which set will be
your standard set? You would want to conform to the notations adopted by a CASE
tool you are required to use in your database project.
Review of Components and Notations
Figure 7-21 highlights many of the standard components and notations used in
entity-relationship modeling. Carefully review the notations or symbols.
The following is a recapitulation of components:
Entity Type
Strong
Weak
Attribute
Simple, single-valued
Composite
Multivalued
Derived
Search WWH ::
Custom Search