Database Reference
In-Depth Information
Diamond
represents a
relationship
”1“ represents
the one part of
the relationship
”n“ represents
the many part of the
relationship
1
n
Rep
Represents
Customer
218
FIGURE 6-34
One-to-many relationship
In Figure 6-35, the many-to-many relationship between orders and parts is represented as
“
m
”
to
“
n.
”
”n“ also represents
the many part of the
relationship
”m“ represents
the many part of the
relationship
m
n
Orders
OrderLine
Part
FIGURE 6-35
Many-to-many relationship
Finally, the many-to-many-to-many relationship between sales reps, customers, and parts is represented
as
“
m
”
to
“
n
”
to
“
p,
”
as shown in Figure 6-36.
Customer
”m“ represents
the many part of the
relationship
”n“ also represents
the many part of the
relationship
n
m
p
Rep
Sold
Part
”p“ also represents
the many part of the
relationship
FIGURE 6-36
Many-to-many-to-many relationship
If desired, you can also indicate attributes in the E-R model by placing them in ovals and attaching them
to the corresponding rectangles (entities), as shown in Figure 6-37. As in the relational model representation,
primary keys are underlined.
