Unit 1( modelling concepts & class modeling)

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Prerequisite
The course is aimed at:
 Students who have prior knowledge to the concept of
Software Engineering.
 Object oriented language like C++.

Polymorphism - Ability of different objects to response same
message in different ways.
Circle
Rectangle
Triangle
Draw

Inheritance
One class can be used to derive another via
inheritance
Classes can be organized into hierarchies
6
Bank
Account
Account
Charge
Account
Savings
Account
Checking
Account

Learning Outcomes:
At the end of the course the student would have the:
 The Knowledge of the basic concepts of Object oriented modeling and
Design.
 Will be able to use the Object Oriented notations and process that extends
from analysis through design to implementations.
 Be able to use all the standard UML notations.
 Capable to model the requirements with use cases and describe the dynamic
behavior and structure of the design.
 Easily create a modular design with components and relate the logical
design to the physical environment.
 The Student will be able to use the concept of design patterns and apply it
where suitable.

What is UML?
UML: Unified Modeling Language
An industry-standard graphical language for specifying,
visualizing, constructing and documenting the software
systems, as well as for business modeling.
The UML uses mostly graphical notations to express the
OO modeling and design of software projects.
Simplifies the complex process of software design

Why we use UML?
 Use graphical notation: more clearly than natural language and code.
 Help acquire an overall view of a system.
 UML is not dependent on any one language or technology.

How to use UML diagrams to design software system?
Types of UML Diagrams:
 Use Case Diagram
 Class Diagram
 Sequence Diagram
 Collaboration Diagram
 State Diagram

Different Views
14
Users Designers Analyzers

UML Diagram –
The Unified Modeling Language (UML) is a standard language for
15
Specifying Visualizing Constructing Documenting
Business Modeling Communications

UNIT – 1 : Introduction-Modeling Concepts, class Modeling
What is Object Orientation? What is OO development? OO themes;
Evidence for usefulness of OO development; OO modeling history
Modeling as Design Technique: Modeling; abstraction; The three models.
Class Modeling: Object and class concepts; Link and associations concepts;
Generalization and inheritance; A sample class model; Navigation of class
models; Practical tips.

Object-Oriented Modelling and
Design
Object-Oriented Modelling and Design is a way of
thinking about problems using models organized around
real world concepts. The fundamental construct is the
object, which combines both data and behaviour.

Objects
An object has:
state - descriptive characteristics
behaviors - what it can do (or what can be done to it)
The state of a bank account includes its account number and its
current balance
The behaviors associated with a bank account include the
ability to make deposits and withdrawals
Note that the behavior of an object might change its state
18

19
Objects
• Objects have three responsibilities:
What they know about themselves – (e.g., Attributes)
What they do – (e.g., Operations)
What they know about other objects – (e.g., Relationships)

Objects
Software objects model read-world objects or abstract concepts
• dog, bicycle, Bank account
Real-world objects have states and behaviors
• Dogs' states: name, color, breed, hungry
• Dogs' behaviors: barking fetching
• Bicycle ‘s State :
• Bicycle’ s behavior :
Other examples of objects are:
myself – an instructor object.
you – a student object
this room – a room object
this university
your car, etc.

What is Object-Orientation about?
One of the key challenges faced by Computer Scientist is how to handle complexity.
Two main concepts used to manage complexity are Modularity and Abstractions.
Modularity means breaking a large system up into smaller pieces until each
peace becomes simple enough to be handled easily.
Abstraction focus on essential aspects of an application while ignoring details.
Over the years, computer scientists have developed a number of approaches to
achieve modularity and abstraction.
The latest of these approaches is Object-Orientation or OO for short.
The key concept in OO is of course Object,

Object-Oriented
Software is organized as a collection of discrete objects that
incorporate both State and behavior.
 Four aspects (characteristics) required by an OO
approach are -
Identity
Classification
Polymorphism
Inheritance
23

Identity
 Identity means that data is organized into discrete,
distinguishable entities called objects.
 E.g. for objects: personal computer, bicycle
 Objects can be concrete (such as a file in a file system) or
conceptual (such as scheduling policy in a multiprocessing
OS). Each object has its own inherent identity. (i.e two objects
are distinct even if all their attribute values are identical).
24

Classification
It means that objects with same data structure (attribute) and
behavior (operations) are grouped into a class.
Each object is said to be an instance of its class.
A class is simply a representation of a type of object. It is the
blueprint/ plan/ template that describe the details of an object.
 A class is the blueprint from which the individual objects are
created.
26

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CCCCllllaaaassssssss AAAAttttttttrrrriiiibbbbuuuutttteeeessss
27
AAAAccccccccoooouuuunnnntttt
++OOwwnneerr:: PPeerrssoonn
++AAmmoouunntt:: ddoouubbllee
++ssuussppeenndd(())
++ddeeppoossiitt((ssuumm::ddoouubbllee))
++wwiitthhddrraaww((ssuumm::ddoouubbllee))
OOOOppppeeeerrrraaaattttiiiioooonnnnssss

CCllaasssseess aanndd OObbjjeeccttss –– EExxaammppllee
CCCCllllaaaassssssss iiiivvvvaaaannnnAAAAccccccccoooouuuunnnntttt
28
AAAAccccccccoooouuuunnnntttt
++OOwwnneerr:: PPeerrssoonn
++AAmmoouunntt:: ddoouubbllee
++ssuussppeenndd(())
++ddeeppoossiitt((ssuumm::ddoouubbllee))
++wwiitthhddrraaww((ssuumm::ddoouubbllee))
++OOwwnneerr==““AABBCC""
++AAmmoouunntt==55000000..00
ppppeeeetttteeeerrrrAAAAccccccccoooouuuunnnntttt
++OOwwnneerr==““XXYYZZ""
kkkkiiiirrrriiiillllAAAAccccccccoooouuuunnnntttt
++OOwwnneerr==““CCSSEE””
OOOObbbbjjjjeeeecccctttt

Polymorphism
It means that the same operation (i.e. action or
transformation that the object performs) may behave
differently on different classes.
Ability of different objects to response same message in
different ways.
30

Polymorphism
Circle
Rectangle
Triangle
Draw

Inheritance
It is the sharing of attributes and operations among
classes based on a hierarchical relationship.
Subclasses can be formed from broadly defined class.
Each subclass incorporates or inherits all the
properties of its super class and adds its own unique
properties.
32

Object-Oriented Development
Development refers to Software Life Cycle.
OOD approach encourages software developers to
work and think in terms of the application domain
through most of the software engineering life cycle.
34

Software Life Cycle
Software life cycle (or software process) - series of
identifiable stages that a software product undergoes
during its life time.
 Feasibility study
 Requirements analysis and specification
 Design
 Coding
 Testing
 Maintenance

Object-Oriented Methodology
 The process for OO development and graphical notation for
representing OO concepts consists of building a model of an
application and then adding details to it during design.
The methodology has the following stages:
 System conception : Software development begins with business
analysis or users conceiving an application and formulating tentative
requirements
 Analysis : The analyst must work with the requestor to understand
the problem, because problem statements are rarely complete or
correct.
The analysis model is a precise abstraction of what the desired
system must do, not how it will be done.
It should not contain implementation decisions.
38

Object-oriented methodology
The analysis model has 2 parts:
Domain model - a description of the real-world objects reflected
within the system
Eg: Domain objects for a stock broker
Application – model - a description of the parts of the application
system itself that are visible to the user.
Eg:- Application might include stock, bond, trade and commission.
Application objects might control the execution of trades and present
the results.

 System design: The development teams devise a high – level
strategy – the system architecture for solving the application
problem.
They also establish policies that will serve as a default for the
subsequent, more detailed portions of design.
The system designer must decide what performance characteristics to
optimize, choose a strategy of attacking the problem and make
tentative resource allocations.
 Class design : The class designer adds details to the analysis model
in accordance with the system design strategy.
The focus of class design is the data structures and algorithms needed
to implement each class.

Implementation : Implementers translate the classes and
relationships developed during class design into particular
programming language, database or hardware.
During implementation, it is important to follow good software
engineering practice so that traceability to the design is
apparent and so that the system remains flexible and
extensible.

Object oriented Themes
Abstraction: let’s focus on essential aspects of an application while
ignoring details.
Encapsulation :( Information Hiding) separates the external aspects
of an object , that are accessible to other objects from internal
implementation details.
Sharing (reuse)
Emphasis on the essence of an object: OO technology stresses
what an object is, rather than how it is used.
Synergy: Identity, classification, polymorphism, and inheritance
characterize OO languages. Use all together.

Evidence for usefulness of OO development
Applications at General Electric Research and Development Center.(1990)
OO techniques for developing compilers, graphics, user interfaces,
databases ,an OO language, etc.
OO technology is a part of the computer science and software engineering
mainstream.
Important forums: (OOPSLA,ECOOP) Object Oriented Programming
systems, Languages and applications. European Conference on OOP.

OO Modeling history
 Work at GE R&D led to OMT(Object-Modeling Technique) in
1991.
Rumbaugh, Grady Booch on unifying the OMT and Booch Notaions
in 1994.
In 1996 the OMG(Object Management Group) issued a request for
the proposals for a standard OO modeling notation.
1997 UML was accepted by OMG as a standard.
In 2001 OMG released UML
Added features and released UML in 2004.
www.omg.org

Year & Version of UML
2000: UML 1.3
1998: UML 1.2
1997: UML 1.0, 1.1
1996: UML 0.9 & 0.91
1995: Unified Method 0.8
2011:UML 2.4
2010:UML2.3
2009:UML2.2
2007: UML 2.1.1
2005: UML 2.0
2003: UML 1.5
2001: UML 1.4

What is Modeling
Modeling consists of building an abstraction of reality.
Abstractions are simplifications because:
They ignore irrelevant details and
They only represent the relevant details.
What is relevant or irrelevant depends on the purpose of the
model.

50
What is a Model
A model is a simplification of reality.
A model may provide
blueprints of a system
Organization of the system
Dynamic of the system

MODEL
 A model is an abstraction, before building any system a
prototype may be developed. The main purpose of model is
for understanding of the system.
Designer build different kinds of models for various purposes
before constructing things.
For example car , airplane, blueprints of machine parts, Plan
for house construction etc., Models serve many purposes

55
Importance of Modeling
Models help us
to visualize a system as it is or as we want it to be.
to specify the structure or behavior of a system.
in providing a template that guides us in constructing a
system.
in providing documenting the decisions we have made.

Purpose of Modeling
Designers build many kinds of models for various purposes
before constructing things.
Models serve several purposes –
Testing a physical entity before building (simulation)
Communication with customer
Visualization
Reduction of complexity
Better understanding of the problem

Purpose of Modeling
Communication with customers
Architects and product designers build models to show
their customers. Mock ups are demonstration products that
imitate some or all of the external behaviour of a system.

Purpose of Modeling
Visualization
Storyboards of movies, television shows and
advertisements let writers see how their ideas flow. They
can modify awkward transitions, and unnecessary
segments before detailed writing begins.

Purpose of Modeling
Reduction of complexity
The main reason for modeling is to deal with systems that
are too complex to understand directly. Models reduce
complexity by separating out a small number of important
things to deal with at a time.

Three models
We use three kinds of models to describe a system from different
view points.
1.Class Model for the objects in the system & their
relationships.
2. State model—for the life history of objects.
Show how systems behave internally
3. Interaction Model—for the interaction among objects.
Show the behaviour of systems in terms of how objects interact
with each other

Class diagrams
Class diagrams provide a graphic notation for modeling
classes and their relationships, thereby describing possible
objects
Note: An object diagram shows individual objects and their
relationships.

Class diagrams
ClassName
attributes
operations
A class is a description of a set of
objects that share the same attributes,
operations, relationships, and semantics.
Graphically, a class is rendered as a
rectangle, usually including its name,
attributes, and operations in separate,
designated compartments.

Class Names
ClassName
attributes
operations
The name of the class is the only required
tag in the graphical representation of a
class. It always appears in the top-most
compartment.

Class Attributes
Person
name : String
address : Address
birthdate : Date
ssn : Id
An attribute is a named property of a
class that describes the object being modeled.
In the class diagram, attributes appear in
the second compartment just below the
name-compartment.

Class Operations
Person
name : String
address : Address
birthdate : Date
ssn : Id
eat
sleep
work
play
Operations describe the class behavior
and appear in the third compartment.

An example of Class
Account_Name
- Custom_Name
- Balance
+AddFunds( )
+WithDraw( )
+Transfer( )
Name
Attributes
Operations

Conventions used (UML) in
Class Diagrams

Conventions used (UML):
• UML symbol for both classes and objects is box.
• Objects are modeled using box with object name followed by colon followed
by class name, Both the names are underlined.
• Use boldface to list class name, center the name in the box and capitalize the
first letter. Use singular nouns for names of classes.
• To run together multiword names (such as JoeSmith), separate the words
With intervening capital letter.

Values and Attributes:
Value is a piece of data.
Attribute is a named property of a class that describes a
value held by each object of the class.
E.g. Attributes: Name, bdate, weight.
Values: JoeSmith, 21 October 1983, 64.

List attributes in the 2nd compartment of the class box.
A colon precedes the type, an equal sign precedes default value.
Show attribute name in regular face, left align the name in the box and use
small case for the first letter.
Similarly we may also include attribute values in the 2nd compartment of
object boxes with same conventions.

Do not list object identifiers

Operations and Methods:
An operation is a function or procedure that maybe applied to
or by objects in a class.
E.g. Hire, fire and pay dividend are operations on Class
Company. Open, close, hide and redisplay are operations on
class window.
A method is the implementation of an operation for a class.
E.g. In class file, print is an operation you could implement
different methods to print files.
Note: Same operation may apply to many different classes. Such
an operation is polymorphic.

UML conventions used –
List operations in 3rd compartment of class box.
List operation name in regular face, left align and use lower case for first
letter.
Optional details like argument list and return type may follow each operation
name.
Parenthesis enclose an argument list, commas separate the arguments. A
colon precedes the result type.
Note: We do not list operations for objects, because they do not vary among
objects of same class.

76
Links and Association
Links and associations are the means for establishing
relationships among objects and classes.
A link is a physical or conceptual connection among objects.
E.g. JoeSmith WorksFor Simplex Company.
An association is a description of a group of links with common
structure and common semantics.
E.g. a person WorksFor a company.

Link is a line between objects
Association connects related classes and is also denoted by a line.
Show link and association names in italics.

Association
Associations are inherently bi-directional.
The association name is usually read in a particular direction
but the binary association may be traversed in either direction.

79
UML Association Notation
 In the UML, a navigable association is represented by an open arrow.
BankAccount Person

80
UML Binary Association Notation
A binary association is drawn as a solid path connecting two classes
or both ends may be connected to the same class.
Company Person
• Self Associated Person
involving class Person

Associations: Multiplicity
Multiplicity defines the number of
objects associated with an instance of
the association.
UML diagrams explicitly list
multiplicity at the end of association
lines.
Intervals are used to express
multiplicity:
transports
Car Person
passenger
transports
5
Car Person
passenger
transports
*
Car Person
passenger
transports
1..*
Car Person
passenger
transports
2..5
Car Person
passenger

82
Associations and Multiplicity
An association is used to show how two classes are related to each other
Symbols indicating multiplicity are shown at each end of the
association

Many-to-one
– Bank has many ATMs, ATM knows only 1 bank
One-to-many
– Inventory has many items, items know 1 inventory

Analyzing and validating associations
Many-to-one
 A company has many employees,
 An employee can only work for one company.
 A company can have zero employees
 E.g. a ‘shell’ company
 It is not possible to be an employee unless you work for a company
Employee * worksFor 1 Company
© 85

Many-to-many
 A secretary can work for many managers
 A manager can have many secretaries
Managers can have a group of secretaries
 Some managers might have zero secretaries.
Secretary *
1..** Manager
supervisor
© 86

One-to-one
 For each company, there is exactly one board of directors
 A board is the board of only one company
 A company must always have a board
 A board must always be of some company
Company 1 1 BoardOfDirectors
© 87

Association Relationships
If two classes in a model need to communicate with each other, there must be link
between them.
An association denotes that link.
Student Instructor

Association Relationships (Cont’d)
We can indicate the multiplicity of an association by adding
multiplicity relationships to the line denoting the association.
The example indicates that a Student has one or more
Instructors:
Student Instructor
1..*

The example indicates that every Instructor has one or more Students:
Student Instructor
1..*

We can also indicate the behavior of an object in an association (i.e.,
the role of an object) using rolenames.
teaches learns from
Student Instructor
1..* 1..*

Multiplicity Constraints
is registered for>
Coming up: Questions
Student
1..*
is held during>
Class
Section
Semester
1
Course
Instructor
1..*
Department
takes>
teaches>
sponsors>
<works for
1..*
is instance of>
1 1..*
1
0..8
0..*
1..3 0..6

Association Ends
Associations have ends. They are called ‘Association Ends’.
They may have names (which often appear in problem
descriptions).

Association Ends
Use of association end names is optional.
But association end names are useful for traversing associations.
Association end names are necessary for associations between
objects of the same class.
When constructing class diagrams you should properly use
association end names and not introduce a separate class for each
reference. Two instances represent a person with a child one for child
and one for parent.
In the correct model, one person instance participates in2 or more
links, twice as a parent and zero or more times as a child.

Example of association ends use

Association: ordering, bag, sequence
On a ‘many” association end, sometimes, it is required that objects
have an explicit order. In this case the ordering is an inherent part of
the association
A workstation screen contains a number of overlapping windows. Each
window on a screen occurs at most once. The windows have an explicit
order so only the topmost window is visible.
The ordering is an inherent part of the association. If objects indicate
ordered set objects by
writing ―{ordered} next to appropriate ‖ association end.
Example:

Association: ordering, bag, sequence
A bag is a collection of elements with duplicates allowed.
A sequence is an ordered collection of elements with duplicates allowed
Bag: collection of elements with duplicates allowed.
• Sequence: ordered collection of elements with duplicate allowed eg. An
itinerary is a sequence of airports and the same airport can be visited more
than once.
• Sequence is ordered bag allow duplicates, {ordered} and {sequence}
only difference is sequence allows duplicates as shown in figure 14.

Association class
 UML offers the ability to describe links of association with
attributes like any class.
An association class is an association that is also a class.

Association class
Examples:

Qualified Association
A qualified association is an association in which an attribute called
Qualifier the objects for a ‘many’ association’ end.
A qualifier selects among the target objects, reducing the effective
multiplicity from ‘many’ to ‘one’.
Both below models are acceptable but the qualified model adds
information.

Qualified Association
Example:

W ithout qualification
Directory
File
filename
1
W ith qualification
*
1 0..1
Directory filename File
Figure 5-9. Example of how a qualified association reduces multiplicity (UML class diagram). Adding a qualifier
clarifies the class diagram and increases the conveyed information. In this case, the model including the qualification
denotes that the name of a file is unique within a directory.

105
Generalization
Deriving a class out of a parent class having some inherited property(from
the parent class) and some new property of the derived class.
The term generalization is for the inheritance in the bottom to the up
direction i.e. from derived class to the parent class.
Generalization is the relationship between a class (superclass) and one or
more variations of the class (subclasses).
A superclass holds common attributes, attributes and associations.
The subclasses adds specific attributes, operations, and associations. They
inherit the features of their superclass.
Generalization is called a “IS A” relationship

• It is represented by a solid line with a large arrow
head pointing towards the parent class.
• Example:
106
Vehicle
Car Truck

Generalization
Customer
Corporate
Customer
Personal
Customer

Generalization
Relationships
Software Design (UML)
Person
A generalization connects a subclass
to its superclass. It denotes an
inheritance of attributes and behavior
from the superclass to the subclass and
indicates a specialization in the subclass
of the more general superclass.
Student

109
Generalization Relationships
Vehicle
Bus Truck Car
Boeing 737
BoeingAirplane
Boeing 757 Boeing 767

Supertype
Subtype2
Subtype1
-
Regular
Customer
Loyalty
Customer
Example: Customer

Incident
LowPriority Emergency Disaster
CatInTree EarthQuake ChemicalLeak
TrafficAccident BuildingFire
Figure 5-10. An example of a generalization hierarchy (UML class diagram). The root of the hierarchy represents the
most general concept, whereas the leaves nodes represent the most specialized concepts.

Use of generalization
Used for three purposes:
Support of polymorphism:
polymorphism increases the flexibility of software.
Adding a new subclass and automatically inheriting superclass
behavior.
Structuring the description of objects:
Forming a classification, organizing objects according to their
similarities. It is much more profound than modeling each class
individually and in isolation of other similar classes.
Enabling code reuse:
Reuse is more productive than repeatedly writing code from scratch.

Generalization, Specialization, and Inheritance
The terms generalization, specialization, and inheritance all refer to aspects
of the same idea.
Generalization and specialization concern a relationship among classes and
take opposite perspectives, viewed from the superclass or from the
subclasses.
Generalization derives from the fact that the superclass generalizes the
subclasses
Specialization refers to the fact that the subclasses refine or specialize the
superclass.
Inheritance is the mechanism for sharing attributes, operations, and
associations via the generalization/specialization relationship.
Generalization represents a relationship at the conceptual level
Inheritance is an implementation technique

115
Poor Generalization Example
(violates the “is a” or “is a kind of” heuristic)
Person
attributes
operations
Arm
attributes
operations
Leg
attributes
operations
Head
attributes
operations

Class model for managing credit card accounts
MailingAddress
address
phoneNumber
CreditCardAccount
maximumCredit
currentBalance
statementDate
Institution
name
address
phoneNumber
accountNumber
Customer
name
Statement
paymentDueDate
financeCharge
minimumPayment
Transaction
transactionDat
e
explanation
amount
transactionNumbe
r
CashAdvance Interest Purchase Fee
feeType
Adjustment
Merchant
name
1 *
*
*
0..1
1
1 0..1
*
1
accountHolder

122
Overloading vs. Overriding
Overloading deals with
multiple methods in the
same class with the same
name but different
signatures
Overloading lets you
define a similar operation
in different ways for
different data
Overriding deals with two
methods, one in a parent
class and one in a child
class, that have the same
signature
Overriding lets you define
a similar operation in
different ways for different
object types

Unit 1( modelling concepts & class modeling)

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