Page 54 - DCAP308_OBJECT_ORIENTED_ANALYSIS_AND_DESIGN

Object Oriented Analysis and Design

Notes

Task Illustrate how aggregation is considered as a form of association.

Self Assessment

Fill in the blanks:

13. .................... is a tightly coupled form of association with some extra semantics.
14. In a .................... aggregation, number and subtypes are fixed i.e. predefined.
15. A .................... aggregate contains, directly or indirectly, is an instance of the same aggregate.

4.5 Summary

Instantiation is the relationship between an object and its class. The notation for instantiation
is a dashed line from the instance to the class with an arrow pointing to the class.
A class attribute is an attribute whose value is common to a group of objects in a class
rather than peculiar to each instance.
Attribute multiplicity specifies the possible number of values for an attribute and is listed
in brackets after the attribute name.

A candidate key for a class is a combination of one or more attributes that uniquely
identifies objects within a class.

An association end is an endpoint of the line drawn for an association, and it connects the
association to a class.
The degree of an association is the number of roles for each link. Associations may be
binary, ternary, or higher degree.
Ternary association is an association among three classes. On the same line, n-ary
association is an association among n classes.

Aggregation is the “part-whole” or “a-part- of” relationship in which objects representing
the component of something are associated with an object representing the entire assembly.

4.6 Keywords

Aggregation: Aggregation is a tightly coupled form of association with some extra semantics.

Association end: An association end is an endpoint of the line drawn for an association, and it
connects the association to a class.
Candidate key: A candidate key for a class is a combination of one or more attributes that
uniquely identifies objects within a class.
Class attribute: A class attribute is an attribute whose value is common to a group of objects in
a class rather than peculiar to each instance.
Domain: A domain is the named set of possible values for an attribute.
Instantiation: Instantiation is the relationship between an object and its class.
Multiplicity: Attribute multiplicity specifies the possible number of values for an attribute and
is listed in brackets after the attribute name.

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