Systems analysis and design methods 7th whitten and benley chapter 08

Object ModelingSystem Concepts for Object Modeling  Classes, Generalization, and Specialization  The class supertype will have one or more one-to-one relationships to object class sub

Object Modeling

Introduction

 The chapter will address the following questions:

 What is object modeling and what are its benefits?

 How do you discover objects and classes, and their relationships?

Object Modeling

An Introduction to Object

Modeling

and design is called object-oriented analysis.

study existing objects to see if they can be reused or adapted for new uses, and to (2) define new or modified objects that will be combined with existing objects into a useful business computing application

referred to as object modeling

the systems environment, and the relationships between those objects

Object Modeling

System Concepts for Object Modeling

 Objects, Attributes, Methods, and Encapsulation

the concept of objects that exist within a system’s environment

 Webster’s Dictionary definition of an object

 Something that is or is capable of being seen, touched, or otherwise sensed.

definition of an object is as follows:

 An object is something that is or is capable of being seen,

touched, or otherwise sensed, and about which users store data and associate behavior

Object Modeling

System Concepts for Object Modeling

 Objects, Attributes, Methods, and Encapsulation

 The types of objects may include a person, place, thing, or event.

person objects

 A particular warehouse, regional office, building, and room are

examples of place objects

appearing on a users display monitor are examples of thing

objects

 An order, payment, invoice, application, registration, and

reservation are examples of event objects

Object Modeling

System Concepts for Object Modeling

 Objects, Attributes, Methods, and Encapsulation

attributes.

 Attributes are the data that represent characteristics of interest

about an object.

WORK ADDRESS, TYPE OF CUSTOMER, HOME PHONE, WORK PHONE, CREDIT LIMIT, AVAILABLE CREDIT, ACCOUNT BALANCE, and ACCOUNT STATUS.

• An instance (or object instance) of an object consists of the values for

the attributes that describe a specific person, place, thing, or event.

Object Modeling

System Concepts for Object Modeling

 Objects, Attributes, Methods, and Encapsulation

 What is the “behavior” of an object

which correspond to functions that act on the object’s data (or attributes)

 In object-oriented circles, an object’s behavior is commonly

referred to as a method or service.

 An object is solely responsible for carrying out any functions

or behaviors that act upon its own data (or attributes)

• For example, only YOU (an object) may CHANGE (behavior)

your LAST NAME and HOME ADDRESS (attributes about you)

Object Modeling

System Concepts for Object Modeling

 Objects, Attributes, Methods, and Encapsulation

 Encapsulation, an important concept

Object Modeling

System Concepts for Object Modeling

 Classes, Generalization, and Specialization

categorizing objects into classes.

 A class is a set of objects that share common attributes and

behavior A class is sometimes referred to as an object class.

thing-objects that have some similar attributes and behavior and could be classified as BOOKs

 A class may also have sub-classes of objects

be members of the class PERSON

Object Modeling

System Concepts for Object Modeling

 Classes, Generalization, and Specialization

 When levels of classes are identified, the concept of inheritance is

applied

object class can be inherited or reused by another object class

between objects/classes is referred to as

generalization/specialization.

attributes and behaviors that are common to several types of an object classes are grouped into their own class, called a

supertype The attributes and methods of the supertype object

Object Modeling

System Concepts for Object Modeling

 Classes, Generalization, and Specialization

 When levels of classes are identified, the concept of inheritance is

applied.

class can be inherited or reused by another object class.

 In the object class PERSON, STUDENT and TEACHER example,

PERSON is referred to as a supertype (or generalization class) whereas STUDENT and TEACHER are referred to as subtypes (or specialization class)

 A class supertype is an entity whose instances store attributes that are

common to one or more class subtypes

 A class subtype is an object class whose instances inherit some

common attributes from a class supertype, and then add other attributes that are unique to an instances of the subtype.

Object Modeling

System Concepts for Object Modeling

 Classes, Generalization, and Specialization

 The class supertype will have one or more one-to-one relationships

to object class subtypes.

 These relationships are sometimes called “IS A” relationships (or “WAS A”, or “COULD BE A”) because each instance of the supertype “is also an” instance of one or more subtypes

 Using OMT notation, classes are represented on an object model as

a rectangle

 The rectangle is divided into three portions

• The top portion contains the name of the class.

• The middle portion contains the name of the common attributes of interest.

Object Modeling

(Customer) customer number = 412209 last name = Bentley first name = Lonnie home phone = 317-463-9593 street = 2625 Darwin Drive

city = West Lafayette state = Indiana zipcode = 47906 etc.

copyright = 1996

Person Class (supertype)

Student Class

(c)

Open

ISBN type title copyright Book

Object Modeling

walk jump talk sleep eat etc.

last name first name birthdate gender Person

Object Modeling

System Concepts for Object Modeling

 Object/Class Relationships

 Objects and classes do not exist in isolation

 The things they represent interact with, and impact one another

to support the business mission

 Thus there is an object/class relationship

• An object/class relationship is a natural business association that

exists between one or more objects/classes

 For example, consider the object classes customer and order that may exist in a typical information system and how they interact

• a CUSTOMER PLACES zero or more ORDERs

• an ORDER IS PLACED BY one and only one CUSTOMERs

 A verb phrase describes the relationship.

 All relationships are implicitly bi-directional, meaning that they can interpreted in both directions

occurrences of one object/class for a single occurrence of the related object/class

 Because all relationships are bi-directional, multiplicity must

be defined in both directions for every relationship

means one and only one

means zero or more

means zero or one

(a)

Object Modeling

System Concepts for Object Modeling

 Object/Class Relationships

 What are aggregation class relationships?

 Sometimes objects/classes are made up of other objects/classes

This type of relationship is called aggregation

• It is also sometimes referred to as “whole-part” or “part-of”

relationships

objects, including: COVER, TABLE OF CONTENTS, CHAPTER, and INDEX objects

• The CHAPTER object contains PAGE objects, which in turn

contain PARAGRAPH objects, which in turn contain WORD objects, and so forth.

individual objects within it

 Multiplicity is also specified for aggregate relationships

1 +

1 +

Object Modeling

System Concepts for Object Modeling

 Objects/Classes interact or "communicate" with one another by

passing messages

method (behavior) to request information or some action

receiving object is organized internally or how the behavior is to

be accomplished, only that it responds to the request in a defined way

well-Object Modeling

Customer

add order modify order delete order display status etc.

order number order date order status etc.

Order

display order status

of order 23161

MESSAGE REQUEST

(containing name of request behavior and attribute needed by ORDER)

Object Modeling

System Concepts for Object Modeling

object-oriented techniques, it means that a behavior may be completed differently for different objects/classes

 The requesting object knows the what service (or behavior) to

request and from which object However, the requesting object does not need to worry about how a behavior is accomplished

Object Modeling

The Process of Object Modeling

 Performing Object Oriented Analysis (OOA)

system and its functional requirements

 OOA requires that we identify the objects, their data attributes, associated behavior, and relationships which support the required business system functionality

the data and behavior they encapsulate, plus their relationships with other objects

 Finding and identifying the business objects

 Organizing the objects and identifying their relationships

Object Modeling

The Process of Object Modeling

 Finding And Identifying The Business Objects

 In trying to identify objects, many methodology experts

recommend the technique of searching the requirements document

or other associated documentation and underline the nouns which may represent potential objects

nouns

and identifying objects, is a technique called Use Case Modeling

developed by Dr Ivar Jacobson

business events, who initiated them, and how the system responds to them

Object Modeling

The Process of Object Modeling

 Finding And Identifying The Business Objects

functionality into many smaller statements of system functionality

called use cases or business events

 A use case a behaviorally related sequence of steps (a

scenario), both automated and manual for the purpose of completing a single business task

 This smaller format simplifies and makes more efficient the technique of underlining the nouns

 It identifies and describes the system functions from the perspective of external users

Object Modeling

The Process of Object Modeling

 Finding And Identifying The Business Objects

 Use Cases are initiated by users or systems called Actors.

 An actor represents anything that needs to interact with the

system to exchange information An actor is a user, a role, which could be an external system as well as a person

• An actor initiates system activity, a use case, for the purpose of

completing some business task

• An actor represents a role fulfilled by a user interacting with the system and is not meant to portray a single individual or job title

• For events that are triggered by time called temporal events, the

actor is the system itself

Object Modeling

The Process of Object Modeling

 Finding And Identifying The Business Objects

 Use cases provide the following benefits:

 As a basis to help identify objects and their high level relationships and responsibilities

 An effective tool for validating requirements

 As a basis for a test plan

 As a basis for a user’s manual

Object Modeling

The Process of Object Modeling

 Finding And Identifying The Business Objects

 A good place to find potential actors and use cases is by analyzing the context model diagram of the system

• If an external party initiates the input, it is considered an actor.

• Some of the inputs are self explanatory, but others may be

misleading, it is always wise to confirm your findings with the system’s business analyst.

Object Modeling

Warehouse

Member Services System Club Member

Marketing Department

Potential Member

Subscription Offer

New Subscription

New Membership Plan & Subscrition Offer Sales & Promotion Reports Order To Be Filled

Club Promtion

Promotion Order

Member Services Context Model

New Monthly or Seasonal Promotion

Past Member

Subscrition Renewal Offer Subscrition Renewal

Member Credit Status

Accounts Receivable Data Base

Regular Order

Member Services Department

Membership Reports

Object Modeling

Club Member initiates Submit Promotion Order

Submit Regular Order Potential Member initiates Submit New Subscription

Past Member initiates Submit Subscription Renewal Member Services Department initiates Request Membership Rpts.

Marketing Department initiates Create New Monthly Promotion

Create New Seasonal Promotion Create New Subscription Program Request Promotion Rpts.

Request Sales Rpts.

Member Services System initiates Send New Subscription Offer

Send Club Promotion Send Subscription Renewal Offer

Object Modeling

The Process of Object Modeling

 Finding And Identifying The Business Objects

system scope and boundaries in terms of use cases and actors

 The use case model diagram represents the relationships between the actors and use cases defined for each business subsystem

• The subsystems represent logical functional areas of business

processes

• The partitioning of system behavior into subsystems is very

important in understanding the system architecture and is very key

to defining your development strategy — which use cases will be developed first and by who.

Object Modeling

M ember Services Department

M arketing Department

M ember Services System

Request Promotion Rpts.

Reques t

M embers hip Rpts.

Request Sales Rpts.

Create N ew Subs cription Program

Create N ew

M onthly Promotion

Submit N ew Subscription

Send N ew Subscription Offer

Submit Subscription Renewal

Send Subscription Renewal Offer

Submit Promotion Order

Send Club Promotion

Submit Regular Order

Member Services System Use Case Model

Promotions Subsystem

Orders Subsystem

Membership

Subsystem

Object Modeling

The Process of Object Modeling

 Finding And Identifying The Business Objects

 For each use case identified, use case’s normal course of events must be documented

 A use case’s normal course of events is a step by step description starting with the actor initiating the use case until the end of the business event

• At this point we only include the major steps which happen the

majority of the time (its normal course)

• Exception conditions or conditional branching logic will be

documented in a later step.

Object Modeling

USE CASE

USE CASE NAME: Submit Promotion Order

DESCRIPTION: Describes the process when a club member submits a club promotion order to either

indicate the products they are interested in ordering or declining to order during this promotion.

3 The promotion order is verified to see if product is being ordered.

4 The club member’s credit status is checked with Accounts Receivable to make sure no payments are outstanding.

5 For each product being ordered, validate the product number.

6 For each product being ordered, check the availability in inventory and record the ordered product information which include “quantify being ordered” and give each ordered product a status of “open”.

7 Create a Picking Ticket for the promotion order containing all ordered products which have a status “open”.

8 Route the Picking Ticket to the Warehouse.

PRE-CONDITION: Use case Send Club Motion has been processed.

POST-CONDITION: Promotion order has been recorded and the Picking Ticket has been routed to the

Warehouse.

ASSUMPTIONS:

A B

C

D

E

F

Object Modeling

The Process of Object Modeling

 Finding And Identifying The Business Objects

use case leaving the system in a state that is a precondition for another use case

to model dependencies

Object Modeling

The Process of Object Modeling

 Finding And Identifying The Business Objects

• Helps facilitate project management by depicting which use cases

are more critical (have the most dependencies) and thus need to have a higher priority.