OO DomainModeling With UML Class Diagrams and

CRC CardsChapter 6

Princess Nourah bint Abdulrahman UniversityCollege of Computer and Information Sciences

Department of Computer Science

Dr. Doaa Sami Khafaga

Objectives

The main objective of this chapter is to know: how to properly use the most essential features of UML class diagrams, and the typical problems you will encounter when modeling with class diagrams.

In this chapter we:

● Introduce the evolutionary approach for building classes

● Explain how to identify objects and attributes of classes

● Describe the technique of CRC ‘Class Responsibility and Collaborator’

● Explain how classes are related in a class diagram

● Explain generalization, association, aggregation and composition

● Introduce object diagramsS.H2009

Software Engineering OO Domain Modeling

What is a Domain Model?● Use cases looked at the system’s

environment (actors) and the system’s external behavior.

● Use cases consider the system as a black box and help us understand how the system as a whole interacts with the outside word.

● Now we turn to consider the inside of the system. We do this by building the domain model, which shows what the black box (the system) encloses.

● uses cases elaborate the system’s behavioral characteristics (sequence of stimulus-response steps),

● domain model gives details of the systems structural characteristics (system parts and their arrangement)

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What is a Domain Model?

● uses cases elaborate the system’s behavioral characteristics (sequence of stimulus-response steps),

● domain model gives details of the systems structural characteristics (system parts and their arrangement)

● The next step is to model the inside of the system. We do this by building the domain model, which shows what the black box (the system) encloses.S.H

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What is a Domain Model?

● Illustrates meaningful concepts in the problem domain.

● Usually expressed in the form of static diagrams (in Rational this implies a high-level class diagram).

● Is a representation of real-world things; not software components (of the system under development).

● No operations are defined or specified in the conceptual model.

● Should show concepts, associations between concepts, and attributes of concepts.

● Serves as a source of software objects.

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What is a Domain Model?

Objectives

● identify concepts related to current development cycle requirements

● create initial conceptual model

● Identify attributed

● add specification concepts

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What is a Domain Model?

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What constitutes a good model?

A model should● use a standard notation● be understandable by clients and users● lead software engineers to have insights

about the system● provide abstraction.

Models are used:● to help create designs● to permit analysis and review of those

designs● as the core documentation describing

the system.S.H2009

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From Use Cases to: Objects, Attributes, Operations (methods) -“evolutionary ”

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Building the Domain Model

A useful strategy for building a domain model is to start with:

● the “boundary” concepts that interact directly with the actors

● and then identify the internal concepts

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Domain Model Relationships

Domain Model

Interaction Diagrams

Dynamic Behavior

Conceptual Class DiagramClasses, attributes, associations

Domain objects

Use Case Model

Functional Requirements

Define terms

Glossary

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Steps to create a Domain Model

Steps

● Identify Candidate Conceptual classes

● Draw them in a Domain Model

● Add associations necessary to record the relationships that must be retained

● Add attributes necessary for information to be preserved

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Find conceptual classes

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Use a category list

● Finding concepts using the concept category list :

● Physical objects: register, airplane, blood pressure monitor

● Places: airport, hospital

● Catalogs: Product Catalog

● Transactions: Sale, Payment, reservation

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Identify conceptual classes from noun phrases

● Finding concepts using Noun Phrase identification in the textual description of the domain .

● Noun phrases may also be attributes or parameters rather than classes:● If it stores state information or it has multiple

behaviors, then it’s a class● If it’s just a number or a string, then it’s

probably an attributeS.H2009

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Identifying objects

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Identifying Operations ‘methods’

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Objects

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Example: Identify conceptual classes from noun phrasesConsider the following problem description, analyzed for Subjects, Verbs, Objects:

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The ATM verifies whether the customer's card number and PIN are correct.

SC V R O O A O AIf it is, then the customer can check the account balance, deposit cash, and withdraw cash.

S R V O A V O AV O A

Checking the balance simply displays the account balance.S M O A V O A

Depositing asks the customer to enter the amount, then updates the account balance.

M S V O R V OA V OAWithdraw cash asks the customer for the amount to withdraw; if the account has enough cash,

S M A O V O R OA V S C V O A

the account balance is updated. The ATM prints the customer’s account balance on a receipt.

O A V C S V O A

O

Analyze each subject and object as follows:● Does it represent a person performing an action? Then it’s an actor, ‘R’.● Is it also a verb (such as ‘deposit’)? Then it may be a method, ‘M’.● Is it a simple value, such as ‘color’ (string) or

‘money’ (number)? Then it is probably an attribute, ‘A’.

●Which NPs are unmarked? Make it ‘C’ for class. Verbs can also be classes, for example:● Deposit is a class if it retains state

information

Mapping parts of speech to object model components [Abbott, 1983]

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Part of Speech

Model Component

Examples

Proper noun Instance AliCommon noun Class Student,

Customer,..Doing verb Operation Buy, check,..Being verb Inheritance Is a kind of, is

one of eitherHaving verb Aggregati

on (Composition)

Has, consists of, includes

Modal verb Constraints Must beAdjective attributes

Attributes 3 years old

Example: a typical description

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Mapping parts of speech to object model components

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Identify conceptual classes from noun phrases: POS

● Examine use case descriptions.● Example: Process Sale use case:

● Main success scenario:● Customer arrives at a POS checkout counter.● Cashier starts a new sale.● Cashier enters an item ID.● System records sale line item. It then presents a

description of the item, its price, and a running total.

● ….● ….

● Possible source of confusion: Is it an attribute or a concept?

● If X is not a number or a text then it probably is a conceptual class.S.H

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Example: Initial POS domain model

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SalesLineItem Item

Sale

Register

StorePayment

Class and Class diagram

• Class naming: Use singular namesbecause each class represents a generalized version of asingular object.

• Class diagrams are at the core of OO Engineering.

• Things naturally fall into categories (computers, automobiles, trees...).

• We refer to these categories as classes.

• An object class is an abstraction over a set of objects with common:

•attributes (states)•and the services (operations)

(methods) provided by each object

• Class diagrams provide the representations used by the developers.

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Example: Initial POS domain model

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Example: Initial Domain model of the Monopoly Game

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Example: Domain model of the Monopoly Game

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Agile modeling style

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Class or Attributes

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Class or Attributes

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Description Class

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Associations

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Associations

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Association, aggregation and composition

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Association between classes Who does What

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When to show association

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Associations and implementation

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Association Notation

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Association Notation

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Naming association

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Applying UML: multiplicity

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Multiplicity values

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Applying UML: multiplicity

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Applying UML: multiplicity

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Multiple association between two classes

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Find association

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Find association

● High priority associations● A is a physical or logical part of B● A is physically or logically contained in/on B● A is recorded in B

● Other associations● A uses or manages or controls B (Pilot -airplane)● A owns B (Airline -airplane)

● Each of the two ends of an association is called a role. Roles have● name● multiplicity expression● navigabilityS.H

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Example: POS Domain Model

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Example: Monopoly Game Partial Domain Model

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Attributes

● Attribute - is a logical data value of an object

● Include the following attributes in a conceptual model● those for which the requirements suggest

or imply a need to remember information

● For example:● Sale needs a dateTime attribute● Store needs a name and address.

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Attributes: UML Notation

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Suitable attribute types

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Data types as attributes

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Attributes are NOT foreign keys

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Generalization

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