Software Design Methodologies:
UML in Action
Dr. Mohamed Fayad, J.D. Edwards Professor
Department of Computer Science & Engineering
University of Nebraska, Lincoln
Ferguson Hall, P.O. Box 880115
Lincoln, NE 68588-0115
http://www.cse.unl.edu/~fayad
May-June 2001
ISISTAN Research Institute – Tandil,
Argentina
Lesson 11:
Object-Oriented
Concepts -2
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May-June 2001
ISISTAN Research Institute – Tandil,
Argentina -- M.E. Fayad
L11-S2
OO Concepts -2
Lesson Objectives
Review of previous lecture
 Discuss associations
 Explore recursive associations,
attributed association
 Understand association constraints
 Understand qualified & derived
associations
 Discuss UML – aggregation

Objectives
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May-June 2001
ISISTAN Research Institute – Tandil,
Argentina -- M.E. Fayad
L11-S3
OO Concepts -2
Associations

An association shows a two-way relationship between
objects (instances) of two or more classes and requiring
special implementation to ensure integrity.

A particular instance of an association is often called a link.

Associations between classes are required if the objects
need to communicate.

Associations are often named, and have role-names for
each side of the link.
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May-June 2001
ISISTAN Research Institute – Tandil,
Argentina -- M.E. Fayad
L11-S4
OO Concepts -2
More on Associations
Association Name
Car
model
year
# of doors
Person
Vehicle Registration
registeredCar
owner
name
age
address
Roles Names
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May-June 2001
ISISTAN Research Institute – Tandil,
Argentina -- M.E. Fayad
L11-S5
OO Concepts -2
More on Associations

Simple example:
Window
displays
0..*
GeomFigure

An association has a name and a numerical specification (multiplicity
indication) of how many objects on one side of the association are
connected with how many objects on the other side.

Associations are called use relationships – even if this may seem
somewhat cheeky in the example below
Company
employs
Employer
May-June 2001
0..*
Person
Employee
ISISTAN Research Institute – Tandil,
Argentina -- M.E. Fayad
L11-S6
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OO Concepts -2
More on Associations

Associations are directed (one way), bidirectional, and
undirected.

UML makes no distinction between bidirectional and
undirected associations.
Multiplicity
Class1
1
role1
May-June 2001
Stereotype
RelationName
{Constraints}
*
Class2
Role2: interface
ISISTAN Research Institute – Tandil,
Argentina -- M.E. Fayad
L11-S7
7
OO Concepts -2
More on Associations

Recursive association: A class has a relation with itself.

It is also possible to model associations that are valid only
temporarily “stereotype or temporary”

Constraints may be used to restrict the relation under
specific aspects.

A role name describes how the object is seen by the
opposite object in the association.

An association can be described in more detail by means of
constraints, tagged values, and stereotypes.

Stereotypes are noted before or above the relation name,
constraints, and tagged values after or below the name.
May-June 2001
ISISTAN Research Institute – Tandil,
Argentina -- M.E. Fayad
L11-S8
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OO Concepts -2
More on Associations

Directed association is a one-way association, in
which one side knows the other, but not vice versa.

Multiplicity Specification:
– 1
exactly one
– 0, 1
zero or one
– 0..4
between zero and four
– 3, 7
either three or seven
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May-June 2001
ISISTAN Research Institute – Tandil,
Argentina -- M.E. Fayad
L11-S9
OO Concepts -2
More on Associations

More multiplicity specifications:
– 0..*
greater than or equal to zero (default)
– *
ditto
– 1..*
greater than or equal to one
– 0..3, 7, 9..* between zero and three, or exactly seven, or
greater than or equal to nine.
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May-June 2001
ISISTAN Research Institute – Tandil,
Argentina -- M.E. Fayad
L11-S10
OO Concepts -2
More on Associations

Recursive associations are associations in which one
class is involved.
has
Patient
Employee
name
staffNo
roomNo
manager
office clerk
*
1
relative
*
Person
leads
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reports to
May-June 2001
ISISTAN Research Institute – Tandil,
Argentina -- M.E. Fayad
L11-S11
OO Concepts -2
N-ary Association

An n-ary association is like a common (binary)
association, except that more than two association
roles involved in it.
N-ary
association
Class1
Class2
Ternary
association
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Class3
May-June 2001
ISISTAN Research Institute – Tandil,
Argentina -- M.E. Fayad
L11-S12
OO Concepts -2
More on n-ary Association
Reservation
Train
date
trainNo
1..*
1
Seat
carriageNo
seatNo
1..*
Passenger
name
title
May-June 2001
ISISTAN Research Institute – Tandil,
Argentina -- M.E. Fayad
Ternary
association
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OO Concepts -2
More on Associations
• Recursive Associations
• N-ary Associations
• Attributed Associations (Association Class)
• Association Constraints
• Qualified Associations
• Derived Associations
• Directed Associations
• Ordered Associations
• Realization/Refinements
• Dependency
May-June 2001
ISISTAN Research Institute – Tandil,
Argentina -- M.E. Fayad
L11-S14
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OO Concepts -2
More on Associations
 Associations are usually bidirectional
 Allows each object involved in the relationship
to refer to the object to which it is related.
 Bidirectional association means at the
relationship has an inverse.
 Associations do not have to be bidirectional.
May-June 2001
ISISTAN Research Institute – Tandil,
Argentina -- M.E. Fayad
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OO Concepts -2
Man
Woman
Marriage
husband
Screen
wife
Association Type
One-to-One
Window
Windows
One-to-Many
(One-to-Zero-or-More)
Nets
Authorization
User
Many-to-Many
Car
Trailer
Zero or One
May-June 2001
ISISTAN Research Institute – Tandil,
Argentina -- M.E. Fayad
L11-S16
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OO Concepts -2
Association Type
Square
Line
Sides
Specified the # of instances
on the “many” side
Secure Room
Male
Person
Occupants
TraditionalFamily
father
mother
Female
Specify the possible # of
instances using “or”
Ternary relationship
children
Child
May-June 2001
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ISISTAN Research Institute – Tandil,
Argentina -- M.E. Fayad
L11-S17
OO Concepts -2
Association Class
Server
Connection
Client
Connection
baudRate
protocol
wireType
disconnect
rerouteLink
• These attributes don’t belong
in either the Client or Server
class.
• They are attributes of the
connection itself.
• The association class can have behaviors as well as attributes.
May-June 2001
ISISTAN Research Institute – Tandil,
Argentina -- M.E. Fayad
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OO Concepts -2
Aggregation & Composite

Aggregation is a special form of association.

Aggregation is used when the relationship is
“part/whole” or “contains/is-part-of”

Aggregation is transitive and operations on
“whole” often cascade down to “parts”.
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May-June 2001
ISISTAN Research Institute – Tandil,
Argentina -- M.E. Fayad
L11-S19
OO Concepts -2
Aggregation & Composite
Server
Aggregation
Computer
“whole”
52
“part”
Client
*
CPU
Disk Drive
Keyboard
Mouse
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May-June 2001
ISISTAN Research Institute – Tandil,
Argentina -- M.E. Fayad
L11-S20
OO Concepts -2
Aggregation & Composite

Special diamond symbol used on “whole” side to indicate
aggregation.

Aggregation is an anti-symmetric that is, if A is part of B,
then B is not part of A.

DO NOT confuse aggregation with generalization

An essential property of aggregates is that the whole acts
as a proxy for its parts.

A composition is a strict form of aggregation, in which the
parts are existence-dependent on the entirely
May-June 2001
ISISTAN Research Institute – Tandil,
Argentina -- M.E. Fayad
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OO Concepts -2
Aggregation & Composite
Aggregation
Part
Entirely
Composition
ExistenceDependentPart
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May-June 2001
ISISTAN Research Institute – Tandil,
Argentina -- M.E. Fayad
L11-S22
OO Concepts -2
Aggregation Problem

Mr. Clinton’s hand is part-of Mr. Clinton & Mr.
Clinton is part-of U.S.A.
May-June 2001

Therefore:

Mr. Clinton’s hand is part-of U.S.A.
ISISTAN Research Institute – Tandil,
Argentina -- M.E. Fayad
L11-S23
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OO Concepts -2
Keypad
Cash Register
Example
*
Number Keys
Total Key
display
Subtotal Key
display
display
drawer
Drawer
Display
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May-June 2001
ISISTAN Research Institute – Tandil,
Argentina -- M.E. Fayad
L11-S24
OO Concepts -2
Aggregation vs. Inheritance
Aggregation
Inheritance
Instances of distinct classes
Instances of a single class
“a-part-of”
“a-kind-of” or “is-a” (AKO)
(APO)
Contains
superclass-of
Aggregate + parts
Superclass + subclass
“and” relationship
“or” relationship
Propagated only if specified
Inheritance
May-June 2001
ISISTAN Research Institute – Tandil,
Argentina -- M.E. Fayad
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OO Concepts -2
Discussion Questions
May-June 2001
•
What is an association? Give examples
•
Associations are usually bidirectional. Please describe.
•
Describe the basic difference between aggregation and
inheritance. What do they have in common?
•
What do you think “multiple inheritance” means?
•
Which type of association is more likely to yield savings in the
amount of code required for implementation? why?
•
Define the process of identifying objects, classes, inheritance,
associations & aggregation, attributes, and behaviors
•
Define Polymorphism with examples
•
What do we mean by saying “Model/View/Controller”?
ISISTAN Research Institute – Tandil,
Argentina -- M.E. Fayad
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OO Concepts -2
Questions for the Next Lecture
Define:
– Use Case
– Structured English
What are the good, bad, and ugly of Use
Case?
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May-June 2001
ISISTAN Research Institute – Tandil,
Argentina -- M.E. Fayad
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OO Concepts -2