Database Reference
In-Depth Information
Meaning of maximum cardinality indicator *
A department entity may be asso-
ciated with many instances of employee.
An employee must be assigned to at least one department, and he or she can be
assigned to only one department
. Note minimum cardinality indicator 1 and
maximum cardinality indicator 1 near DEPARTMENT entity type.
Meaning of minimum cardinality indicator 1
Each employee entity is associated
with at least one department entity. That is, the minimum number of department
instances associated with one employee entity is 1. Notice the solid relationship
line next to EMPLOYEE indicating that the relationship on this side is manda-
tory and that every employee entity participates in the relationship.
Meaning of maximum cardinality indicator 1
An employee entity can be asso-
ciated with one instance of department at most.
Case 2
A department must have at least one employee, but it may have many employees.
Note minimum cardinality indicator 1 and maximum cardinality indicator * near
EMPLOYEE entity type.
Meaning of minimum cardinality indicator 1
Each department entity is associ-
ated with at least one employee entity. That is, the minimum number of employee
instances associated with one department entity is 1. Notice the solid relation-
ship line next to DEPARTMENT indicating that the relationship on this side is
mandatory and that every department entity participates in the relationship.
Meaning of maximum cardinality indicator *
A department entity may be asso-
ciated with many employee entities.
Every employee may not be assigned to a department; if assigned, he or she can
be assigned to only one department
. Note minimum cardinality indicator 0 and
maximum cardinality indicator 1 near DEPARTMENT entity type.
Meaning of minimum cardinality indicator 0
Some employee entities may not
be associated with any department entities. Not every employee entity is associ-
ated with a department entity. That is, the minimum number of department
instances associated with one employee entity is 0. Not every employee entity
participates in the relationship. Notice the dotted or broken relationship line next
to EMPLOYEE entity type, indicating that the relationship on this side is
optional and that not every employee entity participates in the relationship. A
broken or dotted line denotes partial participation in the relationship.
Meaning of maximum cardinality indicator 1
An employee entity can be asso-
ciated with one instance of department at most.
Case 3
Every department may not have employees; if a department has employees, it can
have many employees.
Note minimum cardinality indicator 0 and maximum car-
dinality indicator * near EMPLOYEE entity type.
Search WWH ::
Custom Search