Software design: Lecture 19 - Sheraz Pervaiz
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Software Design
Lecture : 19
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Relationships between Classes
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Association –Discussed in Previous Lecture
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Aggregation Discussed in previous Lecture.
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Composition – Started discussion.
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Inheritance
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Composition – Container and Contained classes
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It’s a strong association.
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It contain Objects that live and die together.
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The composition aggregation relationship is just
another form of the aggregation relationship, but
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Composition Continues....
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Another important feature of composition
aggregation is that the part class can only be
related to one instance of the parent class
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It is represented by a filled diamond shape from
child to parent class with association
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Example of Composition
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Example of Composition
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Example
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Windows Operating Systems
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Aggregation Vs Composition
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Generalization or “ISA”
relationship
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It shows a relationship between super / sub class.
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Sub class inherit public and protected elements
of super class.
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Sub class may override the behaviour of super
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Generalization / Specialization
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Common data elements and methods are put
together in super class (Generalization) and
specific data elements are put together in sub
classes (Specialization)
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Conceptual Generalization
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Generalization Example
Role
attributes
operations
Staff
Faculty
Student
Visitor
attributes
attributes
attributes
attributes
operations
operations
operations
operations
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Example
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Poor Generalization Example
(violates the “is a” or “is a kind of” heuristic)
Person
attributes
operations
Leg
Head
attributes
attributes
attributes
operations
operations
operations
Arm
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