Database Reference
In-Depth Information
Part 1
E1
E1
EMPLOYEE
EMPLOYEE
D1
D1
E2
E2
1,
∗
1,
∗
E3
E3
D2
works in
works in
D2
E4
E4
1,1
0,1
D3
E5
D3
E5
DEPARTMENT
DEPARTMENT
E6
E6
D4
D4
Case 1
Case 2
E7
E7
Figure 7-14
Relationship: optional and mandatory conditions—Part 1.
Part 2
E1
E1
EMPLOYEE
EMPLOYEE
D1
D1
E2
E2
0,
*
0,
*
E3
E3
D2
works in
works in
D2
E4
E4
1,1
0,1
D3
E5
D3
E5
DEPARTMENT
DEPARTMENT
E6
E6
D4
D4
Case 3
Case 4
E7
E7
Figure 7-15
Relationship: optional and mandatory conditions—Part 2.
Meaning of minimum cardinality indicator 1
Each department entity is
associated with at least one employee entity. That is, the minimum number of
employee instances associated with one department entity is 1. Note the solid
relationship line next to DEPARTMENT indicating that the relationship on
this side is mandatory and that every department entity participates in the
relationship.
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