object modeling (2) chapter 3 (2) part 1: modeling concepts object-oriented modeling and design...

Object Modeling (2)

Chapter 3 (2)

Part 1: Modeling Concepts

Object-Oriented Modeling and Design

Byung-Hyun Ha ([email protected])

mailto:[email protected]

Lecture Outline

Introduction

Links and associations

Advanced link and association concepts

Generalization and inheritance

Remaining parts

Introduction

Class and objects A class is abstraction or specification of a group of similar objects e.g. Person vs. Joe, Mary, …

e.g. Every instance of our Vector has x, y, and length().

Person (Person)Joe Smith

24

(Person)Mary Sharp

52name: stringage: integer

public class Vector {

double x;double y;

double length() {double len = Math.sqrt(x * x + y * y);return len;

}}

Introduction

Association vs. links An association is abstraction or specification of a group of similar

links e.g. Has-capital

Country

name

City

name

Has-capital

(Country)Canada

(City)Ottawa

Has-capital

(Country)France

(City)Paris

Has-capital

(Country)Senegal

(City)Dakar

Has-capital

Introduction

Association vs. links (cont’) e.g. Intersects

Line

name

Point

name

Intersects

2+

Links and Associations (cont’)

Multiplicity specification How many instances of one class may related to a single

instance of an associated class

One or many

Optional

Numbers

Playboy Girlloves

Romanticist Girlloves

Boy Girlloves 1+3-5

Links and Associations

Multiplicity depends on problem e.g. tax collection application

e.g. auto workers’ union

It exposes hidden assumption built into the model

Person CompanyWorks-for


Advanced Link and Association Concepts

Role One end of association

Role name A name that uniquely identifies one end of an association


employee employer

User Directory container

contents

owner

authorized user


Role name All role names on the far end of associations attached to a class

must be unique The role name is a derived attribute of the source class

Role name for n-ary association Association of degree 3 or more cannot simply be traversed from

one end to another as binary associations can

Project Language

Person


Link attributes Properties of a link in an association

File UserAccessible by

access permission

/etc/termcap (read) John Doe/etc/termcap (read-write) Mary Brown/usr/doe/.login (read-write) John Doe


Link attributes for one-to-many association e.g. works-for and manages

Person

namesocial security no.address

Company

nameaddress

Works-for

salaryjob title

Manages worker

boss

performance rating


Folding link attributes It is possible to fold link attributes for one-to-one and one-to-

many associations into the class opposite the “one” site How is it possible and which one is preferred?

Person

namesocial security no.address

Company

nameaddress

Works-for

salaryjob title

Person

namesocial security no.addresssalaryjob title

Company

nameaddress

Works-for


Link attributes for ternary association

Pitcher Year

Team

winslosses

W LHarry Eisenstat Cleveland Indians 1939 6 7Harry Eisenstat Detroit Tigers 1939 2 2Willis Hudlin Cleveland Indians 1939 9 10Willis Hudlin Cleveland Indians 1940 2 1Willis Hudlin Washington Senators 1940 1 2Willis Hudlin St. Louis Browns 1940 0 1


Modeling an associations as a class Each link becomes one instance of the class It is useful when links can participate in associations with other

objects or when links are subject to operations

User WorkstationAuthorized on

Authorization

priorityprivileges

start session

Director

home directory


Ordering A special kind of constraint

Window ScreenVisible-on

{ordered}


Qualification A qualified association relates two object classes and a qualifier The qualifier distinguishes among the set of objects at the many

end of an association

Directory File

Directory Filefile name


Examples Ticker symbol of company in stock exchange

Company and office

Stockexchange

Company

ticker symbol

lists

Stockexchange

Company

ticker symbol

lists

Company Personofficeofficerorganization


Aggregation “Part-whole” or “a-part-of” relationship Used for components and assembly

• Existence of a part depends on existence of whole

Tightly coupled form of association extra semantics• Transitivity

• If A is part of B and B is part of C, then A is part of C

• Antisymmetric

• If A is part of B, then B is not part of A

• Propagation of properties

• e.g. location of a door handle is obtained from the door; door obtains its properties from the car, …

Document Paragraph Sentence

Generalization and Inheritance

Generalization The relationship between a class and one or more refined versio

n of it• superclass and subclass

“is-a” relationship Transitive

• ancestor and descendant

• An instance of a subclass is simultaneously an instance of all its ancestor classes

Equipment

namemanufacturerweightcost

Pump Tank

flow rate volume …

Generalization and Inheritance

Examples Fig. 3.23 and 3.24

Some guidelines Do not nest subclasses too deeply “An inheritance hierarchy that is two or three levels deep is certai

nly acceptable; ten levels deep is probably excessive; five or six levels may or may not proper”

Inheritance, generalization, and specialization Different viewpoints of the same relationship

A subclass is a special case of its superclass Don’t borrow a class using inheritance, when the new class is not

really a special case of the original class!

Remaining Parts

Grouping constructs Module and sheet

A sample object model Fig. 3.25: object model for window system

Practical tips …

Homework

HW7 Exercise 3.6 (p. 50)

HW8: extend E3.6a. Modify the class diagram in Figure E3.6 (p. 51) so as to handle u

nary minus and functions (e.g., sqrt(x) for calculating square root of x) with arbitrary number of arguments.

b. Prepare an instance diagram for the class diagram you made for the expression -(B + sqrt(B*B – 4*A*C))/(4*A*A).

object modeling (2) chapter 3 (2) part 1: modeling concepts object-oriented modeling and design...

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