Bài giảng Công nghệ phần mềm nâng cao - Phạm Ngọc Hùng - Class & Object Diagrams

Class & Object Diagrams
Software Design Methodology
2UML Class Diagrams
„ The heart of the UML
„ Describes the classes in the system and 
the relations among them
„ Supports most OO concepts
… associations
… aggregation
… inheritance (including multiple)
3Classes
„ Classes are denoted by rectangles.
‹Attributes
‹Operations 
‹Responsibilities Class
attribute: type
operation
operation(parameters)
responsibility
4Classes
„ Attribute: A named property of a class that 
describes a range of values that instances of 
the property may hold.
„ Operation: Implementation of a service that 
can be requested.
„ Responsibility: A contract or an obligation 
of a class. As the model is refined the 
responsibilities are transformed into 
attributes and operations.
5Object
• Object - a concept, an abstraction, a thing 
meaningful to the domain 
• Joe Smith Person
• Lassie Dog
• flight #713 Flight
• the top window Window
• Object Class - a collection of all objects having the 
same set of features.
• Each object has a unique identity and is an 
instance of its object class.
6Class Diagrams vs. Object Diagrams
Person
name
employeeID
title
Smith:PersonJoe 
p:Person
name=“Yahoo”
employeeID=1212
title=“VP of production”
7Relationships
„ A relationship is a connection among 
things.
„ Common relationships: Dependencies, 
Associations, Generalization and 
Aggregations.
8Dependency
„ A dependency states that a change in 
specification of one thing may effect another 
thing that uses it
Course
CourseSchedule
add(c:Course)
remove(c:course)
Event
Dean
Window
open()
close()
Student
grade
CalculateAverage(grade)
A class takes an object of 
another class as a parameter
A class accesses an object 
of another class
A class calls a class operation 
in another class
9An association is structural relationship that 
specifies that objects of one thing are 
connected to objects of another.
Association
Country
Name: string
Population: integer
Area: Km2
City
Name: string
Population: integer
Has-capital
Binary association
10
Association Name
„Printed at the center of the line
„Describes the nature of the 
relationship (usually a verb)
„A direction triangle can be added
11
Association Multiplicity
„ Used when it is important to state how 
many objects may be connected across 
an instance of an association. 
„ When a number is stated at an end of 
an association it is specified that for 
each object at the class at the opposite 
end there must be that many objects at 
the near end.
„ An * denotes many - which can be any 
number between zero and infinity. 
12
Multiplicity Example
Office
Employee Department
1..*
1..10
1
0..1
At least one employee in a department
An employee belongs to exactly one department
An employee has zero or one office
An office is assigned to a number of one up to 10 
employees
13
Multiplicity symbols 
(participation constraints)
Line
Name: string
Point
Name: string
X-Coordinate: integer
Y-Coordinate: integer
Intersects0,2..* *
Is Endpoint Of 2*
14
Association Classes
„ Denoted as a class attached to the 
association
„ Specify properties of the association
„ Does not belong to any of the connected 
class
Car
Reg. Num.
Model
Year
Person
Name
Year Purchased
* 1.. *Owner of
15
Association Attributes
Works-for
Person
Name: string
ID: string
Address: string
Company
Name: string
Address: string
salary: float
job: string
1..* *
submit
Student
Name
ID
Faculty
Assignment
Number
Subject
Submission date
Grade
140 4
16
Association Role Names
„ Names may be added at each end of the 
association
„ Provide better understanding of the 
association meaning
„ Especially helpful in self-associated 
classes
Person
Manager
Worker
Manages
Company
employee employer
*
1..0
*..1 *
17
Role Names, Constraints and Qualifiers
Ordering
Qualifier:
an attribute that reduces the association’s multiplicity.
owner
User Directory
contents
authorized user
container
1
*
*
*
*
0..1
{ordered}Window Screen
visible-on
* 1
Directory Filefile name
0..1*
Role
18
Classes versus Objects
Class Diagram Object Diagram
Classes name
attributes
operations
responsibility
Association name
multiplicity
role
Association Classes
Objects values for
attributes
Link
Link Object
19
Class Diagram Example
holds
Reader
Name
ID
Address
Copy
Code
Shelf location
Status
Loan duration
Return date
0..1 *
Book
Code
Name
Edition
Author
of
reserved
1
*
*
*{ordered}
20
Object Diagram Example
357:Reader
Name=“Joe”
ID=357
Address=“Jerusalem”
57168-1:Copy
Code=57168-1
Shelf location=681.3.06
Status=“at loan”
Loan duration=2 weeks
holds
Return date=16.11.00
UML:Book
Code=57168
Name=“The Unified Modeling 
Language User Guide”
Edition=1
Author=“Booch, Rumbaugh,
Jacobson”
of
reserved
482:Reader
Name:”Michel”
ID=482
Address=“Haifa”
936:Reader
Name=“David”
ID=936
Address=“Haifa”
57168-2:Copy
Code=57168-2
Shelf location=681.3.06
Status=“at loan”
Loan duration=1 month
holds
Return date=24.11.00
of
21
Aggregation
„ “whole-part” relationship between classes
„ Assemble a class from other classes
Combined with “many” - assemble a class from 
a couple of instances of that class
„ May be replaced by associations...
SentenceParagraph
Picture
Document
text font
pages
*
*
*
22
Aggregation (whole-part; part-of; and)
Monitor
Microcomputer
System 
box Mouse Keyboard
RAM CPU Fan Chassis
aggregate; whole
constituents; parts
0..* 1 0..1 1
* 1 0..1 1
23
Constraint
A functional relationship between entities 
(objects, classes, attributes, links, 
associations) of an object model.
Employee
salary
Window
length
width
boss
{salary < boss.salary} {0.8 ≤length/width≤1.5}
Company Office Person
{ordered}
Member-of
Person Committee
Chair-of
{subset}
0..1
*
*
*
* *
*
24
Constraint (Cont.)
Person
gender:{female, male}
Portfolio
{self.wife.gender=female and 
self.husband.gender=male}
{secured}=Across 
the association 
communicated is 
encrypted. 
BankAccount
Corporation{secured}
{xor}
0..1
wife
0..1
husband
25
Inheritance (Generalization)
„ Denoted by a triangle - connects one 
superclass to many subclasses
„ Multiple inheritance is allowed
… a subclass may be connected to more than one 
superclass
… not recommended - hard to understand, hard to 
implement
„ Four applicable standard constraints:
… Complete
… Incomplete
… disjoint
… overlapping
26
Generalization (gen-spec; kind-of; or)
Figure
color
center position
pen type
Move
Rotate
Display
0 Dimensional 1 Dimensional
Orientation
Scale
2 Dimensional
Orientation
fill type
fill
Scale
Radius
Angle
Arc
Display
Control pts
Spline
Display
Endpoints
Line
Display Diameter
Circle
Display
Endpoints
Polygon
Display
superclass
subclasses
27
Multiple Inheritance
CheckingAccount
BankAccount
InterestBearingItem InsurableItem
Asset
RealEstate Security
SavingAccount Stock Bond
28
Abstract Class - a class that has no direct instances
Class
Concrete 
Class
subclass
Abstract 
Class
Non-leaf 
Class
Leaf 
Class
Instance has direct
instances
superclass
has subclasses
superclass
has subclasses
1..*
1..*
1..*
1..*
29
Recursive Aggregation
Program
Block
Compound
statement
Simple
statement
2..*
1..*
30
Recursive Terms (Multiple Binary term use)
Constant
Value
Expression
Binary Operator
Variable
Name
First Operand
Second Operand
**
1
1
Term
31
(x+y/2)/(x/3+y)
di1:Expression
Binary op=“/”
pl2:Expression
Binary op=“+”
pl1:Expression
Binary op=“+”
di3:Expression
Binary op=“/”
di2:Expression
Binary op=“/”
y:Variable
Name=“y”
two:Constant
Value=2
x:Variable
Name=“x”
three:Constant
Value=3
2nd
1st1st1st
1st
1st
2nd
2nd2nd
2nd
32
Recursive Terms
(Unary &Binary & Single Term Use)
Second Operand
Constant
Value
Expression Variable
Name
First Operand 1
1
Term
Binary Unary
33
Abstract Operations
Hourly
Employee
hourly rate
overtime rate
compute pay
Salaried
Employee
weekly rate
compute pay
Exempt
Employee
monthly rate
compute pay
Employee
year-to-date earnings
compute pay {abstract}
The origin class defines 
the protocol: 
•semantics;
•attribute types;
•number and type of 
arguments for methods
34
Generalization as Extension and Restriction
Extension: addition of new features.
(e.g. Person vs. Student)
Restriction: constraining ancestor 
attributes.
(e.g. nullifying some attributes) 
35
Overriding Operations
„ Tension between use of inheritance for 
abstraction vs. implementation reuse.
„ Reasons for overriding:
… Extension
(e.g. Person has Report_Marriage; Employee has 
Report_Marriage that extends the code of 
Report_Marriage)
… Restriction
(e.g. Subclass operation use some of superclass
sub-operations)
36
Reasons for overriding (cont.)
…Optimization 
e.g. IntegerSet has findMax; SortedIntegerSet has 
another implementation for findMax.
… Convenience
Look for a similar class and use it as superclass.
This is ad hoc use which is semantically wrong.
Better: define a third common class, from which 
both will inherit.
Rule for method overriding:
All methods that implement an operation must 
have the same protocol.