1

The Object

OBJECT

Attributes contained in datastructures

Procedures whichcan operate on thedata structures

Object Identity

Object State

Object behaviour

2

UML and OO Design

3

Some Object Oriented Terminology

The following characteristics are generally understood to be included– Identity: Two Objects with the same attribute values are

distinct.– Classification: Objects with the same attributes and behaviour

are grouped into Classes.– Polymorphism: The same procedure name may be used by

different Classes to invoke different code.– Inheritance: Allows a Class to be defined as a sub-type of

another Class.– Encapsulation: Separates the external interface of an Object

from its internal implementation details.

4

Conventional “Structured Programming” Approach

Data

Call

Data Access

Method

Method

5

Program Modifications

Modifications to Procedures usually require modifications to data and vice versa.

When the application is designed around the procedural aspects of the users business, then the structure of the application must change as the business practice changes.

6

Benefits of OO Design

Objects are more stable building blocks for systems than traditional procedures.

Objects are extensible. Objects are more reusable than procedures alone

because they can be more independent of program context.

End users may relate easily to Object concept. Object Oriented development reduces project risk by

spreading integration across the project life cycle.

7

Layered Software Development

System usingPCBs

PCB using ICs

IC

Applications

Models

Classes

8

OO State Of The Art

Object Oriented programming languages have matured over 20 years (Smalltalk, C++, Object-Pascal, Java).

Development of GUIs like Windows and X have accelerated interest in Object Oriented techniques.

Increasing desire for reusability increases interest in OO. Object Oriented databases still not widely accepted. Analysis and Design methodologies in a constant state of

flux. At present a very big effort is being made to develop a standardised notation, the UML, under the auspices of the OMG.

9

OO Methods (Later…)

Second Generation– Fusion (Coleman)

– Syntropy (Cook & Daniels)

Third Generation– Catalysis (Desouza

& Wills)

First GenerationOMT (Rumbaugh)Booch (Booch)Objectory (Jacobson)

10

OO Development Processes

UML is not a process, it is a set of related notations.

Rational promote Objectory as the process for UML, there are others (three amigos).

Process is related to environment, it must also encourage rigour.

11

UML Overview

Unified nified

Modelling odelling

Languageanguage

UML Models Views Provided by Models. UML Diagram Notation

12

UML Models

Nine different Diagram types providing...Functionality ModelStatic Models Dynamic Models

Provide different (orthogonal and overlapping) views of the system being modelled.

13

Views Provided by Models

UML provides rich set of modelling tools.Different views of system supported by models. Models provide differing perspectives.

Use-case view (externally perceived functionality).Logical view (internal functionality).Component view (organisational).Concurrency view (comms. & synch.).Deployment view (physical architecture).

14

UML Diagram Notations

The DiagramsUse-case DiagramClass DiagramObject DiagramState DiagramSequence DiagramCollaboration DiagramActivity DiagramComponent DiagramDeployment Diagram

Unified nified

Modelling odelling

Languageanguage

15

Use Case Diagram(Mainly used in Analysis)

Insurance SalespersonCustomer

Take out policy

Sales stats.

Customer stats.

16

Use-case Notations

Describe functionality requirements of the system, i.e. functional spec.

May be described in plain text. May be supported by activity diagrams or state

diagrams.

17

Class Diagram

Customer Portfolio Trader

Instrument

Bond StockStock

Option

0..*

0..*cont

ains

1 1..*owns handles

1..* 1

18

Class Diagram Notation

Depicts static structure of classes. Development of Entity-Relationship Diagrams Classes represent things in the system. Classes may be related in many ways…

– Associated

– Dependant

– Specialised

– Packaged

19

State Diagram

Go up(floor)

Go up(floor)

Movingup

idleMovingdown

On firstfloor

Moving tofirst floor

arrived

arrived

Go down(floor)timeout

Arrive first floor

20

State Diagram Notation

Styled on work of David Harel. Used also in OMT, Syntropy and most other OO

methods. Each Class may be modelled with a STD, if

important dynamic behaviour is exhibited by that Class.

21

Sequence Diagram

:Computer :PrintServer :Printer :Queue

Print(file)[printer free]print(file)

[printer busy]store(file)

22

Sequence Diagram Notation

Developed from ITU standard X.100 State Transition Diagram (STD) notation.

Portrays dynamic collaboration between objects. Objects shown in boxes across top. Time marches down the page.

23

Engineering Process for Allocation of Responsibility

Process will lay down rules for timing of allocation of responsibilities to classes.

May use domain analysis, find classes & relationships, then allocate from use cases.

May find classes from use cases.

24

Domain Analysis

Use Natural Language

Problem Domain

NaturalLanguage

25

Natural Language

Nouns suggest candidate Classes. Not every noun is an Object Class.

– Some are attributes of another Class.

– Some are irrelevant, outside the scope of the application.

Verb phrases suggest class associations– some relationships are irrelevant (caution).

Proper nouns suggest Objects of a Class type. Beware of singular nouns.

26

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.

27

Structured Class Description

Class Name: CustomerDescription: Personal or company detailsSuperclass: User

Name: NameDescription: Customer’s nameType: String (max. 12 chars)Cardinality: 1

Name: OwnsDescription: Details of bank accountsType: AccountCardinality: Many

28

Structured Class Description (cont..)

Public Methods:

Name: Pay_billParameters: amount, date, destination, account.Description: Customer may pay bills through the Bank.

29

Structured Class Description (cont..)

Private Methods:

Name: TransferParameters: amount, from_account, to_account.Description: Allow transfers from owned accounts to any others.

30

Static Modelling

Classes and

Relationships

31

Static Modelling

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

32

Classes and Objects

Classes, Objects and their relationships are the primary modelling elements in the OO paradigm.

A class is to a type as an object is to an instance. Classification has been around for a long time, we

apply it now to programs.

33

The Class Diagram

Classname

Classname

attribute: datatype

operation (args: type): type

OR

34

Finding Classes

Use domain analysis as before. Derive them from the use cases (descriptions). Look for data which must be stored or analysed. Are there external systems? Are there any devices under the control of the

system? Are there any organisational parts?

35

Attributes

Describe the state and characteristics of the object.

Must be typed, primitives like integer, real, Boolean, point, area, enumeration, these are primitives. May be language specific.

Visibility may be public (+), private (-) or protected (#).

36

Class variables have scope across every instance of class, change one changes all (C++ static).

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.

37

Example UML Class

Invoice

+ amount :Real+ date : Date = Current_date+ customer : String+ specification : String- administrator: String = “Unspecified”- number_of_invoices: Integer+ status: Status = unpaid {paid, unpaid}

Name, bold

Public, typed

Default value

Class variable

Private, typed, default value

Property

38

Example in Java

public class Invoice{ public double amount; public Date date = new Date(); public String customer; static private int number_of _invoices = 0;

//constructor public Invoice() { number_of_invoices++; }};

39

Example in C++

class Invoice{public Invoice( ); ~Invoice( ); double amount; Date date; char customer[25];private static int number_of _invoices = 0;};

40

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.

41

Syntactic Constructs

Formal syntax is as follows – visibility name(parameter-list) return-type-expression {property-string}

parameter-list specified as …– name: type-expression=default-value

All operations must have unique signature. Default values on parameters are Ok.

42

Figure

- size: Size- pos: Position+ figureCounter: Integer

+ draw( )+ resize(percentX: Integer=25, percentY=30)+ returnPosition( ): Position+ incrementCounter( ): Integer

MyFigure.resize(10,10)MyFigure.resize(27)MyFigure.resize()

percentX=10, percentY=10percentX=27, percentY=30percentX=25, percentY=30

Signatures ?Class scope ?Defaults ?

On the Class Diagram

43

Associations

Associations model Class relationships. Associations should be named where appropriate. Usual

to use verbs from the problem domain. Roles played by classes may also be named. Associations have a cardinality. Rules from programming about sensible names apply.

44Class

Class

Class

Class

Association Name

Exactly One(default)

Zero or more

Optional (zero or one)

One or more

Numerically specified

1.. *

1..5,8

Class1 Class2

Class

Associations & Cardinality

*

0..1

45

Cardinality Examples

RentMember Video

Employee

Name:StringNumber:EmpNo

Dept

Name:Name

HasCustomer Account

AccNo:AccountBalance: Real

1..*

0..1 *

46

Class & Object Representation

RentMember Video

Enemy at the gate: Video

Chocolate: VideoBrianStone: Member

0..1 *

47

Navigable Associations

Used to indicate responsibility, later may be translated into pointer mechanism.

May be bi-directional.

Person Carowns

0..*

48

Roles

Useful for indicating context of a class. Optional construct. Part of the association, not the class

Works forCompany Personemployer employee

*

49

Recursion

Self referential construct. Complex construct, may not be supported by

target language.

UserDirectory container

contents

owner

authorised user* *

*

*

0..1

50

Aggregation & Composition Special type of association, “consists of”,

“contains”, “part of” identify it. Two types

– Shared Aggregation.– Composition Aggregation.

Many notations available.

51

Shared Aggregation

Team Person

Members

* *

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

52

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.

53

Three Composition Notations

Window

Text

Listbox

Button

menu

*

*

*

*

54

Window

Text

Listbox

Button

menu

*

*

*

*

55

Text

Listbox

Button

menu

Window

*

*

*

*

Component not bold.May use syntax

rollname:classnameMultiplicity shown.

56

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.

57

Example

Car

Estate Saloon Hatchback Coupe

General

Specific

58

Normal Generalization

Subclasses inherit from Superclasses. Scope rules apply, public, private and protected

are available (+, -, #). Abstract classes have no Objects. Car class is a good abstract class, denoted with

{abstract} tag under name in top compartment. Abstract operations are tagged also.

59

Subclass Concretises the Abstract

Vehicle

Car Boat

Drive(){abstract}

Drive() Drive()

60

Implementation Issue

Vehicle

Car Boat

Drive(){abstract}

Drive() Drive()

Person

drivesWhen person invokes drive( ), method is bound at runtime.Like Virtual and Pure Virtual function in C++.

This Drive ( ) iscalled

61

Books & References

Visual Modelling with Rational Rose and UML– Terry Quatrani Addison-Wesley

Using UML: software engineering with objects and components. [main text]

– Stevens & Pooley, Addison Wesley, ISBN: 0-201-64860-1

– http://www.dcs.ed.ac.uk/home/pxs/Book/

UML Toolkit– Hans-Erik Eriksson, Magnus Penker,Wiley, 1997, ISBN: 0-471-19161-2

UML Distilled– Martin Fowler, Kendall Scott Addison-Wesley, 1997, ISBN: 0-201-32563-2

Real-Time UML– Bruce Powel Douglas Addison-Wesley