Object Oriented Analysis

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Object Oriented Analysis

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Title: Object Oriented Analysis

1
Object Oriented Analysis Design (OOAD)
2
OOAD

It focuses on objects where system is broken down
in terms of the objects that exist within it.
Functions (behaviour) and data (state) relating
to a single object are self-contained or
encapsulated in one place.

3
Objects

Object is an abstraction of something in a
problem domain, reflecting the capabilities of
the system to keep information about it, interact
with it, or both.
Objects are entities in a software system which
represent instances of real-world and system
entities

4
Objects
Object Identity Behaviors State
An employee Mr. John Join(), Retire() Joined, Retired.
A book Book with title Object Oriented Analysis Design AddExemplar, Rent, available, reserved
A sale Sale no 0015, 15/12/98 SendInvoiced(), Cancel(). Invoiced, cancelled.
5
Object Class

Class is a description of a set of objects that
share the same attributes, operations, methods,
relationship and semantics.
Object classes are templates for objects. They
may be used to create objects.
An object represents a particular instance of a
class.

6
Term of objects

Attribute data items that define object.
Operation function in a class that combine to
form behavior of class.
Methods the actual implementation of procedure
(the body of code that is executed in response to
a request from other objects in the system).

7
Employee object class
Class
Object
Employee16
name John address M Street No.23 dateOfBirth
02/10/65 employeeNo 324 socialecurityNoE342545 d
epartment Sale manager Employee1 salary
2340 stautscurrent taxCode 3432 .
Eployee16.join(02/05/1997) Eployee16.retire(03/08/
2005) Eployee16.changeDetail(X Street No. 12)
8
Encapsulation and Data Hiding

Packaging related data and operations together is
called encapsulation.
Data hiding hides the internal data from
external by methods (interface).

9
Encapsulation

private attributes and methods are encapsulated
within the class, they cannot be seen by clients
of the class
public methods define the interface that the
class provides to its clients

Customer
- numCustomers 0 - MIN_BUDGET 200 - name
String - address String - budget int
private attributes
printNumCustomer( ) void
public methods
placeOrder( ) void
Customer class
10
Object communication

Objects communicate with each other by sending
messages
a message is a method call from a message-sending
object to a message-receiving object
a message consists of
an object reference which indicates the message
receiver
a method name (corresponding to a method of the
receiver), and
parameters (corresponding to the arguments of the
calling method)
a message-receiving object is a server to a
message-sending object, and the message-sending
object is a client of the server

11
Message Passing
message
name Lawrence employeeNo 15 commission 200
takeOrder(sofa, name, address, 120799)
199
takeOrder( ) int
return value
alex
lawrence
message
lawrence.takeOrder(sofa, 1 Robinson Rd,
120799)
parameters
method name
object reference
12
Message Passing
Customer
SalesPerson
- numCustomers 0 - MIN_BUDGET 200 - name
String - address String - budget int
- MAX_ PRICE 200 - name String - employeeNo
String - commission int
printNumCustomer( ) void
takeOrder( ) void
placeOrder( ) void
takeOrder
alex
lawrence
client
server
13
Inheritance

Object classes may inherit attributes and
services from other object classes.
Inheritance represents the generalization of a
class.

14
A generalisation hierarchy
15
Library class hierarchy
Library Item
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Number of copies
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User class hierarchy
17
Multiple inheritance

Rather than inheriting the attributes and
services from a single parent class, a system
which supports multiple inheritance allows object
classes to inherit from several super-classes
Can lead to semantic conflicts where
attributes/services with the same name in
different super-classes have different semantics
Makes class hierarchy reorganisation more complex

18
Multiple inheritance
19
Advantages of inheritance

It is an abstraction mechanism which may be used
to classify entities
It is a reuse mechanism at both the design and
the programming level
The inheritance graph is a source of
organisational knowledge about domains and systems

20
Problems with inheritance

Object classes are not self-contained. they
cannot be understood without reference to their
super-classes
Designers have a tendency to reuse the
inheritance graph created during analysis. Can
lead to significant inefficiency
The inheritance graphs of analysis, design and
implementation have different functions and
should be separately maintained

21
Inheritance and OOD

There are differing views as to whether
inheritance is fundamental to OOD.
View 1. Identifying the inheritance hierarchy or
network is a fundamental part of object-oriented
design. Obviously this can only be implemented
using an OOPL.
View 2. Inheritance is a useful implementation
concept which allows reuse of attribute and
operation definitions. Identifying an inheritance
hierarchy at the design stage places unnecessary
restrictions on the implementation
Inheritance introduces complexity and this is
undesirable, especially in critical systems

22
Objects Association

Modeling an association between two classes means
that there is some sort of relationship between
objects of each class that may be connected.

studies
Student
Course
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23
Object aggregation

Aggregation model shows how classes which are
collections are composed of other classes
Similar to the part-of relationship in semantic
data models

24
Object aggregation
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25
Object Cohesion Coupling

Cohesion of a component is a measure of how well
it fits together. Each operation provides
functionality which allows the attributes of the
object to be modified, inspected or used as a
basis for service provision.
Coupling is an indication of the strength of
interconnections between program units. Highly
coupled systems have strong interconnections,
with program units dependent on each other
(shared variables, interchange control function).
Loosely coupled system which are independent .

26
Polymorphism

the ability of different objects to perform the
appropriate method in response to the same
message is known as polymorphism.
the selection of the appropriate method depends
on the class used to create the object

27
Example Polymorphism

class Shape
private String name
public Shape(String aName) nameaName
public String getName( ) return name
public float calculateArea( ) return 0.0f
// End Shape class

class Circle extends Shape private float
radius public Circle(String aName)
super(aName) radius 1.0f public
Circle(String aName, float radius)
super(aName) this.radius radius
public float calculateArea() return
(float)3.14fradiusradius // End Circle
class
28

class Square extends Shape
private float side
public Square(String aName) super(aName)
side 1.0f
public Square(String aName, float side)
super(aName) this.side side
public float calculateArea() return (float)
sideside
// End Square class

29
Polymorphism Example
public class ShapeDemoClient public static
void main(String argv ) Shape c1 new
Circle("Circle C1") Shape c2 new
Circle("Circle C2", 3.0f) Shape s1 new
Square("Square S1") Shape s2 new
Square("Square S2", 3.0f) Shape shapeArray
c1, s1, c2, s2 for (int i 0 i lt
shapeArray.length i)
System.out.println("The area of "
shapeArrayi.getName( )
" is " shapeArrayi.calculateArea( )
" sq. cm.") //
End main // End ShapeDemoClient1 class
30
OO Analysis and Design

OO Analysis - examines requirements from the
perspective of the classes and objects found in
the vocabulary of the problem domain. In other
words, the world (of the system) is modelled in
terms of objects and classes.
OO Design - OO decomposition and a notation for
depicting models of the system under development.
Structures are developed whereby sets of objects
collaborate to provide the behaviours that
satisfy the requirements of the problem.

31
Object Oriented Analysis

Analyze the domain problem
Describe the process systems
Identify the objects
Specify attributes
Defining operations
Inter-object Communication

32
Identifying Object

Objects can be
External Entity (e.g., other systems, devices,
people) that produce or consume information to be
used by system
Things (e.g., reports, displays, letters,
signals) that are part of information domain for
the problem
Places (e.g., books room) that establish the
context of the problem and the overall function
of the system.
Organizational units (e.g., division, group,
team, department) that are relevant to an
application,
Transaction (e.g., loan, take course, buy,
order).

33
Example of candidate objects

Just a Line management wishes to increase
security, both in their building and on site,
without antagonizing their employees. They would
also like to prevent people who are not part of
the company from using the Just a Line car park.
It has been decide to issue identity cards to all
employees, which they are expected to wear while
on the Just a Line site. The cards records the
name, department and number of the member of
staff, and permit access to the Just a Line car
park.
A barrier and a card reader are placed at the
entrance to the car park. The driver of an
approaching car insert his or her numbered card
in the card reader, which then checks that the
card number is known to the Just a Line system.
If the card is recognized, the reader sends a
signal to raise the barrier and the car is able
to enter the car park.
At the exit, there is also a barrier, which is
raised when a car wishes to leave the car park.
When there are no spaces in the car park a sign
at the entrance display Full and is only
switched off when a car leaves.
Special visitors cards, which record a number
and the current date, also permit access to the
car park. Visitors cards may be sent out in
advance, or collected from reception. All
visitors cards must be returned to reception
when the visitor leaves Just a Line.

34
Candidate objects

Just a Line management security building
site employee people company
car park card name department
number member of staff access barrier
card reader entrance driver car
system signal exit space
sign visitor reception

35
Candidate objects rejection

duplicates if two or more objects are simply
different names for the same thing.
irrelevant objects which exists in the problem
domain, but which are not intended.
vague when considering words carefully it
sometimes becomes clear that they do not have a
price meaning and cannot be the basis of a useful
in the system.
general the meaning is too broad.
attributes as the attribute of objects.
associations actually represents the
relationships between objects.
roles sometimes objects referred to by the role
they play in a particular part of the system.

36
Rejected Candidate objects
Candidate objects Rejection criteria
Just a Line, member of staff duplicates with company, employee respectively
management,company, building, site, visitor and reception irrelevant to the system
security, people vague
system too general
name, department, attribute
access association
driver role
37
Rest Objects

Car park Staff Card Visitors card
Employee Entrance exit
card reader barrier Full sign
space sensor car

38
Define class attributes
Full sign onboolean switch on() switch off()
Car Park capacity spaces inc.spaces() dec.spaces()
space left()
Barrier type upboolean raise() lower()
Card Reader valid card nos. read card() card OK()
39
Data Dictionary

Barrier type up
type EntranceExit
up truefalse
raise if the barrier is not already raised,
this operation takes as argument an object of the
barrier class and returns an object of the same
class, with the up attribute set to true. If
the barrier is already up, the operation returns
the error message barrier is already raised
lower if the barrier is not already lower, this
operation takes as argument an object of the
barrier class and returns an object of the same
class, with the up attribute set to false. If
the barrier is already down, the operation
returns the error message barrier already
lowered.

40
Objects Relationship
Car Park
Car Park
1 ..
2 ..
2 ..
Card Reader
Barrier
Sensor
1 ..
1
Valid cards
1 ..
Card
Visitors Card
Staff Card
41
Object behaviour modelling

A behavioural model shows the interactions
between objects to produce some particular system
behaviour that is specified as a use-case
Sequence diagrams (or collaboration diagrams) in
the UML are used to model interaction between
objects

42
Sequence Diagram for Entrance
User
CarPark
Sensor
CardReader
Valid card
Barrier
Full Sign
Full Sign off
Car present
Check space left
Yes
Card number
Card number
Card OK
Card returned
Raise
Car not present
lower
Decrement Space
Check space left
Yes
43
OO Analysis and Design

Object-Oriented (OO) development is very
different from structured development
Structured approach focuses on major functions
within a system and on the data used by the
functions.
OO approach focuses on the objects in a system
and on the relationships between those objects.

Unlike functional decomposition, OO views a
complex problem as a meaningful collection of
objects that collaborate to achieve some higher
level behaviour gt closely mirrors how people
view complex problems gt using OO should make the
job of developing large, complex systems more
manageable.

45
Object Oriented Model
46
Structured Model
47
Comparison