Analysis and Design with UML:
Classes and Relationships
Bina Ramamurthy
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Introduction
Purpose of this part is to transform the
requirement analysis represented by the usecase diagram(s) to design diagrams using
static analysis.
The result of this phase is UML class
diagrams consisting of classes and
relationship among them.
We will study techniques to discover classes
and the UML notations for representing class
diagrams.
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Topics for Discussion
Classes, Responsibility, Collaboration
(CRC) method for discovering classes
and assigning responsibility.
Class-based Analysis and Design: UML
notations, class diagrams.
Case Studies.
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CRC Card Method
Although proponents of the object paradigm often
say that identifying objects is a simple and intuitive
process, a number of noted experts admit that this is
not always true! …The solution is to use the CRC
process to determine the classes necessary to the
system as part of the design process for the
application. CRC (classes, responsibility, and
collaboration) cards can be used to visualize and test
different class-based models during the design
phase. It is a proven technique used and advocated
by leading methodologists.
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CRC Card
Class Name
Collaborations
Responsibilities
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CRC Card Example
Weather Station
Responsibilities
1. Select 24hr/Current
2. Set Date Time
3. Display Current
1. Temp(T)
2. Wind (W)
3. Pressure (P)
4. Humidity (H)
4. Display 24hours
1. Hi/Lo for (TWPH)
5. Display Trends in TWPH
6. Calibrate
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Collaborations
User Interface(UI)
Date
Time
Temp
Wind
Pressure
Humidity
Calibrator
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CRC Card: UserInterface
UserInterface
Collaborators
Responsibilities
Keypad
1.
2.
3.
4.
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Display
Input date
Input time
Input selection
Display data
Temp
Wind
Pressure
Humidity
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CRC Card: Keypad
Collaborators
Keypad
Date
Responsibilities
Time
1. Store date
2. Store time
3. Store selection
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Selection
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CRC Card: Temperature
Temperature
Collaborations
Responsibilities
T.Device
1. Measure and Record temperature
2. Determine and record Hi/Lo
3. Determine trend
StatDataBase
Date
Time
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Class Discovery
The entries in the collaborations column are
possible classes or non-software entities.
In this case these are: UserInterface, Display,
Tempertaure, Wind, Pressure, Humidity,
StatDataBase, Selection, Date, Time, Keypad,
Callibrator.
The responsibility of designing one or more of
these classes can be assigned to the
members of the group who participated in
this discovery process.
On to relations among classes and class
diagrams.
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Classes
OO paradigm supports the view that a system
is made up of objects interacting by message
passing.
Classes represent collection of objects of the
same type.
An object is an instance of a class.
A class is defined by its properties and its
behaviors.
A class diagram describes the static view of a
system in terms of classes and relationships
among the classes.
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Discovering Classes
(Alternative)
Underline the nouns in a problem statement.
Using the problem context and general
knowledge about the problem domain decide
on the important nouns.
Design and implement classes to represent
the nouns.
Underline the verbs. Verbs related to a class
may represent the behavior of the class.
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Examples
Drawing package: Design a user interface for
drawing various shapes: circle, square,
rectangle.
Football scores: Keep track of football score.
General purpose counter: To keep of track of
count for various applications.
Library: Books, different categories of books,
details of student borrower, library
personnel.
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Designing Classes
A class represents a class of objects.
A class contains the data declarations (“parts”) and
methods (“behaviors” or “capabilities” ).
OO Design:
Class properties or characteristics are answers to “What is
it made of?” (It has a ____, ____, etc.)
Behaviors, capabilities or operations are answers to “What
can it do?” (verbs in the problem)
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Classes are Blueprints
A class defines the general nature of a collection of
objects of the same type.
The process creating an object from a class is called
instantiation.
Every object is an instance of a particular class.
There can be many instances of objects from the
same class possible with different values for data.
A class structure implements encapsulation as well as
access control: private, public, protected.
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Example
objects
Object
References
redRose
class Rose
blueRose
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class
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Class Diagram : Automobile
Automobile
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public:
seat
seatBelt
accelerator
private:
sparkPlugs
gear
protected:
gloveCompartment
public:
startEngine
brake
protected: transmission
private: fuelInjection
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Automobile Class Using
Rational Rose Tool
Automobile
seat
seatBelt
acceleratorPedal
sparkPlugs
gear
gloveCompartment
startEngine( )
brake( )
transmission( )
fuelInjection( )
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Access Control
Public, protected, private
Public properties and behaviors are available
to any other object to use/invoke
Private: available only within the objects.
Protected: available within the objects and to
the class hierarchy inherited from the class.
(We will discuss more about this when
dealing with OO concept Inheritance.)
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Relationships
Typically an application consists of
many related classes.
Commonly used relationships include:
associations, aggregations, and
generalizations.
We will look into other relationships
later. (Focus in this lecture will be on
general class diagrams.)
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Association
An association is a connection between
classes, a semantic connection between
objects of classes involved in the association.
Association typically represents “has a” or
“uses” relationships.
Indicated by a line,



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sometimes with arrow indicating unidirectional
relationship,
adorned by the name of the relation, and
the ends of the line adorned by cardinality of
relationship and optionally by the roles connected
to each class.
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Association : Examples
Person
Uses
Computer
A person uses a computer.
Person
Owns
0..*
Car
A person may own many (zero..many) cars.
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Roles in Association
drives
Person
driver
company car
Car
A person (driver) drives a (company) car.
wife
Person
husband
married to
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Aggregation
Aggregation represents a relation
“contains”, “is a part of”, “whole-part”
relation.
Indicated by a line adorned on the
“whole” by a hollow diamond


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Along with name of relationship and
Cardinality.
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Aggregation: Example
League
contains
Team
*
Membership aggregation: A league is made up of
Many teams.
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Auto
made of
1
*
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wheel
engine
Strong aggregation.
part
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Generalization
Generalization is a relationship between a
general and a specific class.
The specific class called the subclass inherits
from the general class, called the superclass.
Public and protected properties (attributes)
and behaviors (operations) are inherited.
Design representation “inheritance” OO
concept.
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Generalization: Symbol
It represents “is a” relationship among
classes and objects.
Represented by a line with an hollow
arrow head pointing to the superclass
at the superclass end.
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Generalization: Example
Vehicle
Car
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Boat
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Truck
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Combined Example
drives
Person
0..*
Car
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Vehicle
Boat
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Truck
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Summary
We looked at Class Diagrams which is very
important part of UML Model, perhaps the
only model used in many design
representation.
We also looked at two methods for class
discovery(/analysis): CRC Card Method and
Nouns-Verbs.
Class diagrams directly represent the
implementation (code) classes and the
relationship among them.
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