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Unit 3: Class Modelling

Notes
Figure 3.4: Association
Association name

Student University
Registered in

Class Class

!
Caution Every association has roles.
For example, in Figure 3.5 you can see that two classes, Student and University, have their
defined roles. Here you can also see that binary association has two roles, one from each class.
Figure 3.5: Roles in Association

Role
Student University

Study Teach

Associations may be binary, ternary, or have higher order. In exercise, the vast majority of
association is binary or ternary associations. But a ternary association is formed compulsion;
they cannot be converted into binary association.

Did u know? If a ternary association is decomposed in some other association, some
information will be lost.

Example: In Figure 3.6 you can see a ternary association.
Figure 3.6: Ternary Association

Student Teacher

Class

Task Make distinction between binary and ternary association.

3.2.2 Multiplicity

Multiplicity in an association specifies how many objects participate in a relationship. Multiplicity
decides the number of related objects. Multiplicity is generally explained as “one” or “many,”
but in general it is a subset of the non-negative integers.

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