OBJECT ORIENTED ANALYSIS

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CHAPTER 6

• OBJECT ORIENTED ANALYSIS

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Learning Objectives

• Understand object oriented concepts
• Be able to understand and/or draw object oriented
  analysis modeling
• Use case diagram
• Activity diagram
• Class diagram
• Sequence diagram
• Collaboration diagram
• State diagram

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Object-Oriented Concepts

• Must be understood to apply class-based elements
  of the analysis model
• Key concepts
• Classes and objects
• Attributes and operations
• Encapsulation and instantiation
• Inheritance

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Classes

• object-oriented thinking begins with the
  definition of a class, often defined as
• template
• generalized description
• blueprint ... describing a collection of
  similar items
• a superclass establishes a hierarchy of classes
• once a class of items is defined, a specific
  instance of the class can be identified

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Building a Class
Class name
Attributes
Operations
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Encapsulation/Hiding
Class encapsulates both data and the
logical procedures required to manipulate the data
Reduces the propagation of side effects when
changes occur
method 2
method 1
data
method 3
method 6
method 4
method 5
Achieves information hiding
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Class Hierarchy
PieceOfFurniture (superclass)
Table
Chair
Desk
Chable"
Subclass inherit both attributes and operations
from a superclass
subclasses of the
Subclasses of the furniture superclass
Instances of chair
instances of Chair
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Methods(a.k.a. Operations, Services)
An executable procedure that is encapsulated in a
class and is designed to operate on one or more
data attributes that are defined as part of the
class. A method is invoked via message passing.
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Attributes
A collection of data values that describe a
class
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• Objects

• Instances of a specific class
• Inherit a class attributes and operations
• Class STUDENT
• Object instance (object) Ali
• attributes name, date of birth, etc.
• operations calc_age, calc_cgpa, etc.

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Example
STUDENT
Name DOB Address Phone
Calculate_age Calculate_gpa Register_course
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Object Oriented Analysis (OOA)

• Based on objects rather than data or processes
• The intent of OOA is to define all classes (and
  the relationships and behavior with them) that
  are relevant to the problem to be solved
• There are various OOA methods. Booch Method,
  Jacobson Method and Rumbaugh Method have
  collaborated into.

Unified Approach Unified Modeling Language (UML)
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THE OOA PROCESS
Use Case Modeling shows functions
Class-based Modeling Class diagram, CRC
Behavioral Model State Diagram, Sequence Diagram
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• USE CASE MODELING
• Illustrates the manner in which an actor
  interacts with the system
• Actor Anything that communicates with the
  system and that is external to the system
• Can be people or devices
• Represent the roles that people/devices play as
  the system operates
• Use Case
• Depiction of a systems behavior or functionality
  under various conditions as the system responds
  to requests from users
• Full functioning for a specific business purpose

Represent actor
Represent a use case
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Use-Cases

• A collection of user scenarios that describe the
  thread of usage of a system
• Each scenario is described from the point-of-view
  of an actor
• Each scenario answers the following questions
  (eg refer handout Use Case Template for
  Surveillance)
• Who is the primary actor, the secondary actor
  (s)?
• What are the actors goals?
• What preconditions should exist before the story
  begins?
• What main tasks or functions are performed by the
  actor?
• What extensions might be considered as the story
  is described?
• What variations in the actors interaction are
  possible?
• What system information will the actor acquire,
  produce, or change?
• Will the actor have to inform the system about
  changes in the external environment?
• What information does the actor desire from the
  system?
• Does the actor wish to be informed about
  unexpected changes?

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Use-Case Diagram
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Eg consider the interactions between a Bank
Customer and an ATM
Bank ATM Machine
Withdraw Cash
Check Balance
Bank Customer
Create Online Transaction
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Writing Use-Cases (Scenario)

• Use caseAccess camera surveillance-display
  camera views (ACS-DCV)
• Actorhomeowner
• If Im at remote location, I can use any PC with
  appropriate browser software to log on to the
  SafeHome Products Web site. I enter my user ID
  and two levels of passwords and, once Im
  validated, I have access to all functionality for
  my installed SafeHome system. To access specific
  camera view, I select surveillance from the
  major function buttons displayed, I then select
  pick camera, and the floor plan of the house is
  displayed. I then select the camera that Im
  interested in. Alternatively, I can look at
  thumbnail snapshots from all cameras
  simultaneously by selecting all cameras as my
  viewing choice. Once I choose a camera, I select
  view and a one-frame-per-second view appears in
  a viewing window that is identified by the camera
  ID. If I want to switch cameras, I select pick a
  camera and the original viewing window
  disappears and the floor plan of the house is
  displayed again. I then select the camera that
  Im interested in. A new viewing window appears.
• A variation of this narrative use case is an
  ordered sequence of user actions refer handout
  Use Case Template for Surveillance (Pressman,
  R. (2005). Software Engineering A
  Practitioner's Approach, 6th edition. New York
  McGraw-Hill)
• .

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Use-Case Modeling

• Relationships Between Use Cases
• Use cases may participate in relationships with
  other use-cases
• Two types
• Extends
• Adds new behaviors or actions to a use case
• Include
• One use case references another use case

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Example Use-case diagram for a university
registration system (Correction arrow direction
should be in opposite direction)
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Activity Diagram

• Supplements the use-case by providing a
  diagrammatic representation of procedural flow
• May adds additional detail not directly
  mentioned by the use case

Activity/Function
Flow/Transition
Decision
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An activity diagram for Access Camera surveillance
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ATM Authorization
Masuk kad
Baca kad
Minta PIN
Masuk PIN
Tidak
Sahkan PIN
Adakah sah?
Ya
Pilih servis
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Class-Based Modeling

• Identify analysis classes by examining the
  problem statement
• Use a grammatical parse to isolate potential
  classes
• Identify the attributes of each class
• Identify operations that manipulate the attributes

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Analysis Classes

• External entities (e.g., other systems, devices,
  people) that produce or consume information to be
  used by a computer-based system.
• Things (e.g, reports, displays, letters, signals)
  that are part of the information domain for the
  problem.
• Occurrences or events (e.g., a property transfer
  or the completion of a series of robot movements)
  that occur within the context of system
  operation.
• Roles (e.g., manager, engineer, salesperson)
  played by people who interact with the system.
• Organizational units (e.g., division, group,
  team) that are relevant to an application.
• Places (e.g., manufacturing floor or loading
  dock) that establish the context of the problem
  and the overall function of the system.
• Structures (e.g., sensors, four-wheeled vehicles,
  or computers) that define a class of objects or
  related classes of objects.

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Selecting ClassesCriteria

• Retained Information
• Needed services have a set of identifiable
  operations
• Multiple attributes
• Common attributes
• Common operations
• Essential requirements

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CRC Modeling

• Analysis classes have responsibilities
• Responsibilities are the attributes and
  operations encapsulated by the class
• Analysis classes collaborate with one another
• Collaborators are those classes that are
  required to provide a class with the information
  needed to complete a responsibility.
• In general, a collaboration implies either a
  request for information or a request for some
  action.

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CRC Modeling
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Class Types

• Entity classes, also called model or business
  classes, are extracted directly from the
  statement of the problem (e.g., FloorPlan and
  Sensor).
• Boundary classes are used to create the interface
  (e.g., interactive screen or printed reports)
  that the user sees and interacts with as the
  software is used.
• Controller classes manage a unit of work
  UML03 from start to finish. That is, controller
  classes can be designed to manage
• the creation or update of entity objects
• the instantiation of boundary objects as they
  obtain information from entity objects
• complex communication between sets of objects
• validation of data communicated between objects
  or between the user and the application.

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Responsibilities

• System intelligence should be distributed across
  classes to best address the needs of the problem
• Each responsibility should be stated as generally
  as possible
• Information and the behavior related to it should
  reside within the same class
• Information about one thing should be localized
  with a single class, not distributed across
  multiple classes.
• Responsibilities should be shared among related
  classes, when appropriate.

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Collaborations

• Classes fulfill their responsibilities in one of
  two ways
• A class can use its own operations to manipulate
  its own attributes, thereby fulfilling a
  particular responsibility, or
• a class can collaborate with other classes.
• Collaborations identify relationships between
  classes
• Collaborations are identified by determining
  whether a class can fulfill each responsibility
  itself
• three different generic relationships between
  classes WIR90
• the is-part-of relationship
• the has-knowledge-of relationship
• the depends-upon relationship

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Composite Aggregate Class
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Associations

• Two analysis classes are often related to one
  another in some fashion
• In UML these relationships are called
  associations
• Associations can be refined by indicating
  multiplicity (the term cardinality is used in
  data modeling

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Multiplicity
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Behavioral Modeling

• The behavioral model indicates how software will
  respond to external events or stimuli. To create
  the model, the analyst must perform the following
  steps
• Evaluate all use-cases to fully understand the
  sequence of interaction within the system.
• Identify events that drive the interaction
  sequence and understand how these events relate
  to specific objects.
• Create a sequence for each use-case.
• Build a state diagram for the system.
• Review the behavioral model to verify accuracy
  and consistency.

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State Representations

• In the context of behavioral modeling, two
  different characterizations of states must be
  considered
• the state of each class as the system performs
  its function and
• the state of the system as observed from the
  outside as the system performs its function

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The States of a System

• statea set of observable circum-stances that
  characterizes the behavior of a system at a given
  time
• state transitionthe movement from one state to
  another
• eventan occurrence that causes the system to
  exhibit some predictable form of behavior
• actionprocess that occurs as a consequence of
  making a transition

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Behavioral Modeling

• make a list of the different states of a system
  (How does the system behave?)
• indicate how the system makes a transition from
  one state to another (How does the system change
  state?)
• indicate event
• indicate action
• draw a state diagram or a interaction diagram
  (sequence diagram or collaboration diagram)

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Sequence diagram

• A representation of how events cause flow from
  one object to another as a function of time.
• Events are identified by examining a use case
• Is a shorthand version of a use case
• Sequence diagram consists of
• Objects
• Lifeline
• Messages/Event

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Sequence Diagram
anOrder
Object Object and Class
anOrder Order
Message/event
prepare()
needsToReorder()
Self Delegation
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object
Object A Class A
Object B Class B
messageA( )
message
messageB(string)
messageC( )
activation (optional)
lifeline
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Identifying events with the Use-Case

• Use case for a small portion of the SafeHome
  security function
• The homeowner uses the keypad to key in a
  four-digit password. The password is compared
  with the valid password stored in the system. If
  the password is incorrect, the control panel will
  beep once and reset itself for additional input.
  If the password is correct, the control panel
  awaits further action.

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Sequence Diagram
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Class diagram
Sequence diagram
Bob ClockStaff
Ali User
printRecord( )
STAFF printRecord calculateSalary
CLOCKSTAFF printRecord calculateSalary
COMISSIONSTAFF printRecord calculateSalary
Bob ClockStaff
Ali User
calculateSalary( )
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DeliveryItem
itemnumberquantityetc
new()
is_for
ReOrderItem
StockItem
itemnumberquantityetc
orderNumberminQuantitydateetc
OrderEntryWindow
new()
choose()
check()boolean remove() needsToReorder()
boolean
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AReorder Item
aDelivery Item
new
checktrue new
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Computer
PrintServer
Printer
status() integer
print(file)
uses
print(filename)
print(file)
Managed by
Queue
store(file)
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aComputer Computer
aPrintServer PrintServer
aPrinter Printer
aQueue Queue
aUser User
print(file)
printer free print(file)
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Collaboration Diagram

• Shows the relationships among objects
• Consists of
• Objects
• Lines connecting the objects
• Messages

Object A
Object C
2. Message2 3. Message3
Object B
1. message1
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1. keyInCourseInfo
CourseForm
Interaction diagrams
Student
2. addCourse
CourseForm
AcademicStaff
StudentSchedule
AcademicStaff
Student
3. newCourse
keyInCourseInfo
addCourse
StudentSchedule
newCourse
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State Diagram

• Indicates how an individual class changes state
  based on external events
• Represents states for each class and the events
  (triggers) that cause changes between these
  states
• One state diagram for each class.
• Event causes the transition, the labels for
  each arrow
• Action occurs concurrently with the state
  transition or as a consequence of it. Generally
  involves one or more operations
  (responsibilities)
• Transition represented by an arrow
• Guard condition a boolean condition that must be
  satisfied in order for the transition to occur
• Activity - represents a long-running task during
  that state.
• Actions vs activity
• Actions cannot be interrupted, activity can be
  interrupted by an incoming event. 
• Both represent an operation on the object being
  studied. 
• For example, an operation that sets an attribute
  would be considered an action, while a long
  calculation might be an activity. 

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State-Diagram Notation
An operation that is perform when an object is in
a certain state
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Example State Diagram
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Class CourseSchedule
bina jadual kursus
Initialization
dibuka pd pelajar
ditutup kuota penuh
add student/numStudent0
addstudent numStudent50
Open
Closed
add student numStudentlt50
cancel
cancel
Cancelled
delete
Dibatalkan atau tidak ditawarkan lagi
doSend cancellation notices
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State Diagram for the ControlPanel Class
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State Diagram