3' Analysis

1
3. Analysis

• Overview of OO concepts
• Classes and objects
• Finding classes
• Class Diagram

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3.2 Classes and Objects

• Classes
• Associations
• (Static Modelling)

3
Classes and Objects

• 1 Classes Objects
• 2 The Class Diagram
• 3 Associations
• 4 Aggregation Composition
• 5 Generalisation

4
Classes and Objects

• Classes, Objects and their relationships are the
  primary way to model.
• A class is like a type and therefore an object
  is like a variable.

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An Object has ...

• Attributes (data).
• Behaviour (operations).
• State (memory)
• Identity
• Responsibilities

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An example Object ...

• A sensor
• Attributes (data) Value, Rate of change
• Behaviour (operations) acquire, report ...
• State (memory) Last value, Last Rate
• Identity Robot arm joint sensor
• Responsibilities Gives co-ordinates for arm

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The Class Sensor

• All sensors share certain characteristics hence
  we have a class of sensors.
• But each individual example is an object.
• (An instance of the class)

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Attributes

• Describe the state and characteristics of the
  object.
• Must be typed, primitives like integer, real,
  Boolean, point, area, enumeration. May be
  language specific.
• Visibility may be public (), private (-) or
  protected ().

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Attributes (Contd.)

• Class variables have scope across every instance
  of class, change one changes all.
• Property strings may be used to define allowable
  properties of an attribute. Used for enumeration
  types.
• Syntax
• visibility name type-expression initial-value
  property-string
• Only name and type are mandatory.

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Example Class
Name, bold
Public, typed
Sensor
Linear_Value Real Rate_Of_Change Real
0.0 Sensor_Name String Sensor_Location
String - Controller String Unspecified -
number_of_sensors Integer status Status
ONON, OFF
Default value
Private, typed, default value
Class variable
Property
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Operations

• Operations manipulate attributes and perform
  other tasks.
• Scope is the Class.
• Operation signature is composed of name,
  parameters and return type.
• name(parameter-list) return-type-expression
• Scope and visibility rules apply.

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Syntactic Constructs

• Formal syntax is as follows
• visibility name(parameter-list)
  return-type-expression property-string
• parameter-list specified as
• name type-expressiondefault-value
• All operations must have unique signature.
• Default values on parameters are Ok.

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On the Class Diagram
Figure
Signatures ? Class scope ? Defaults ?
-size Size -pos Position figCounter Integer
draw() resize(percentX Integer25,
percentY30) returnPos() Position incCounter()
Integer
percentX10, percentY10 percentX27,
percentY30 percentX25, percentY30
MyFigure.resize(10,10) MyFigure.resize(27) MyFigur
e.resize()
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Cardinality Examples
Employee
Dept
1..
NameString NumberEmpNo
NameName

Rent
0..1
Member
Video
Has
Customer
Account
AccNoAccount
Balance Real
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Class Object Representation
0..1

Rent
Member
Video
Night for day Video
John Doe Member
Sunset Boulevard Video
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Navigable Associations

• Used to indicate responsibility, later may be
  translated into pointer mechanism.
• May be bi-directional.

owns
0..
Person
Car
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Recursion

• Self referential construct.
• Complex construct, may not be supported by target
  language.

owner
User
container
Directory


0..1
authorised user

contents
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Qualified Associations

• A qualified association relates two Object
  Classes and a qualifier.
• One-to-many and many-to-many associations may be
  qualified.
• The qualifier distinguishes among the set of
  objects at the many end of an association.

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Qualified Associations

Directory
File
Is more clearly expressed as .....
Directory
File
File name
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Or-Association

• A constraint on two or more associations.
• Objects of a class may participate in at most one
  of the associations at a time.

0..
Insurance Contract
1
0..
Insurance Co
or
1..
1..
Person
Company
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Ordered Association

• Shows implicit order of associations.
• Default is unordered.

ordered
Screen
Window

Visible on
ordered
Sensor
Controller

polls
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Association Class

• Class may be attached to association, and not
  another class.

employer
Company
Person
0..1
Employment
Association Class
Period dateRange
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Shared Aggregation

• One person may be a member of many teams.
• Person is part of team, shared by N teams.

Person
Team
Members
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Composition Aggregation

• More restrictive. Strong ownership here.
• Rules
• Parts live inside whole, parts die with whole,
  like automatic variables.
• Multiplicity on whole side must be 0..1, on
  part side may be anything.
• Composition aggregation forms a tree of parts,
  shared forms a network of parts.

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Three Composition Notations
Text


Listbox
Window

Button
menu

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Window

• Component not bold.
• May use syntax
• rollnameclassname
• Multiplicity shown.

Text

Listbox

Button

menu
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Generalisation

• Generalisation and Inheritance allow sharing of
  similarities among Classes while also preserving
  differences.
• Inheritance refers to mechanism of sharing
  attributes operations between subclasses and
  their superclass.
• Default values of attributes methods for
  operations may be overridden in subclass.

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Example
General
Financial service
Specific
Pension
Mortgage
Personal Loan
Insurance
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Subclass Concretises
FormControl
Display()abstract
ButtonElement
InputElement
Display()
Display()
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Implementation Issue
FormControl

• When Client invokes Display(), method is bound at
  runtime.
• Like pure virtual function in C.

Display()
Display()abstract
Client
ButtonElement
InputElement
Display()
Display()
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Constrained Generalization

• Generalisations may be
• Overlapping inherit multiple subclasses with
  common superclass.
• Disjoint opposite to overlapping.
• Complete all subclasses specified, no more
  allowed.
• Incomplete more subclasses may be added to
  hierarchy.

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Engineering Process for Allocation of
Responsibility

• Process will lay down rules for timing of
  allocation of responsibilities to classes from
  use cases.
• May use domain analysis, find classes
  relationships, then allocate from use cases.
• May find classes from use cases.

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Domain Analysis

• Use Natural Language

Natural Language
Problem Domain
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Class Description

• Develop a Class description, either in textual
  prose or some other structured form. E.G. using a
  customer in a Bank
• Customer a holder of one or more accounts in a
  Bank. A customer can consist of one or more
  persons or companies. A customer can make
  withdrawals deposit money transfer money
  between their accounts or to another account
  query their accounts.

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Structured Class Description
Class Name Customer Description Personal or
company details Superclass User Name
Name Description Customers name Type String
(max. 12 chars) Cardinality 1 Name
Owns Description Details of bank accounts Type
Account Cardinality Many
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Structured Class Description (cont..)
Public Methods Name Pay_bill Parameters
amount, date, destination,
account. Description Customer may pay bills
through the Bank.
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Class Diagram
1..
1..
1
1
owns
handles
Customer
Portfolio
Trader
0..
contains
0..
Instrument
Bond
Stock
Stock Option
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Class Diagram Notation

• Depicts static structure of classes.
• Classes represent things in the system.
• Classes may be related in many ways
• Associated
• Dependant
• Specialised
• Packaged

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Object Diagram
Author
Computer
uses
Class Diagram
NameString ageinteger
NameString memoryinteger
0..1
1..
Object Diagram
LaptopComputer
BrianAuthor
NameDellLT memory32
DesktopComputer
Namebstone age38
NameDellMMX memory32