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The activity diagrams represent the sequence of activities that the static constituents of a system need to perform to complete a process and the state diagrams depict the changes that o

An object-oriented design should represent the structural

and behavioral aspects of a software system Static

modeling is used to represent the structural constituents of

a software system Dynamic modeling is used to represent the behavior of the structural constituents Dynamic

modeling uses various types of diagrams, such as

interaction, state, and activity diagrams

This chapter explains the concept of dynamic modeling

In addition, it explains how to create the dynamic model

of a system by using interaction diagrams

In this chapter, you will learn to:

 Identify the concepts of dynamic modeling

 Create interaction diagrams

Objectives

Dynamic modeling is a UML modeling technique that represents the behavior of the static constituents of a software system Therefore, it is also known as behavioral modeling A designer requires dynamic modeling techniques to represent the interaction, workflow, and different states of the static constituents in a software system

The design of a software system is considered to be the good if it is able to represent what

a system should do and how Without a good design a developer will not be able to code a program correctly This is because coding involves the implementation of the design Modeling techniques are required to represent all aspects of a software system These modeling techniques help in representing the system requirements, the static constituents

of a system, its behavior, and architecture

Dynamic modeling techniques help the designer to represent the behavior of the static constituents so that a developer is able to depict how a system should behave to meet the desired requirements It provides various diagrams such as, interaction, activity, and state diagrams, which help you design the dynamic model of a software system

Consider the example of Wilson Inc., an automobile manufacturing company, which is planning expansion and, for this reason, wants to automate its inventory control The management of Wilson Inc decides to install an inventory management system (IMS) that will organize the stock reorder level, supplier details, and payments for spare parts

The interaction diagram models the interaction between the static constituents of a

software system The activity diagrams represent the sequence of activities that the static constituents of a system need to perform to complete a process and the state diagrams depict the changes that occur in the state of objects because of the interaction among the various constituents of a software system

Introducing Dynamic Modeling Concepts

Need for Dynamic Modeling

Static modeling is required to represent the physical structure of a software system However, it is insufficient as it does not explain how the constituents of the structure behave and interact with each other To depict the behavior of the structural constituents, you need dynamic modeling The following table lists the differences between static and dynamic modeling

Static Modeling Dynamic Modeling

It represents the static or structural

constituents of a software system

Therefore, it is also known as structural

It helps in depicting the relationships

and dependencies between the

constituents of a system

It helps in expressing and modeling the behavior of a system over a period of time Difference between Static and Dynamic Modeling

Difference between Static and Dynamic Modeling

Note

Interaction diagrams depict how the constituents of a software system interact to realize the use cases of the system In addition, you can use interaction diagrams to generate executable code through forward and reverse engineering The two components of an interaction diagram are:

„ Collaboration: Depicts the static aspect of an interaction diagram

„ Interaction: Depicts the dynamic aspect of an interaction diagram

A collaboration is a collection of instances of classes, the relationship among the

instances of classes, and actors A collaboration groups all the components that are

required to realize a use case The relationships among the components of a collaboration are graphically depicted as links between objects A link serves as a path over which messages are sent and received

Although, abstract classes and interfaces do not have instances, they can form a part of

a collaboration

You use interactions to depict the flow of control in an operation or among use cases In

an interaction, an object sends a message to request another object to perform an

operation In other words, an interaction is initiated when one object requests another object to perform certain operations, and in this way, invokes its methods

For example, Wilson Inc has an inventory database that stores the inventory information when a new stock of automobile parts arrives The inventory manager intimates the supplier and orders automobile parts when the stock of a part reaches its reorder level

To design the IMS, the development team creates a collaboration for the use case, order parts, which is realized through the interaction of Order object and the inventory database The various interactions to realize the use case, order parts are:

1 Request by the Inventory Manager actor to the object, O1 of class Order, to perform the operation, issueOrder()

2 Request by the issueOrder() operation to the database to store the information about the order

3 Signal sent by the database to the object, O1, to intimate that the data storage

operation is complete

Creating Interaction Diagrams

Note

The following figure shows the flow of control to realize the order parts use case of the IMS

Interaction Diagram for the Order Parts Use Case

There are multiple slots in a collaboration, called roles, which are filled by objects and links at run time In other words, roles are used to depict the run-time responsibility of the objects of a class and the relationship The two types of roles in a collaboration are:

„ Classifier roles: Describe objects that can form a part of the collaboration

„ Association roles: Describes the links that can form a part of the collaboration

An interaction signifies the collection of communications that occur among the

classifier roles across the association roles A collection of communications indicates

the messages that flow from one classifier role to another

When an object calls the methods of another object, a sequence of messages flow between them The following table lists the various types of messages that can be sent from one object to another and their graphical representation in an interaction diagram

Message Description Graphical Representation

Call Specifies the invocation of a method of

an object

Return Returns a value to the calling method

Send Sends an asynchronous signal to an

object

Create Creates an object

Destroy Destroys an object

The commonly used interaction diagrams are Sequence diagram and Communication diagram Let us, discuss how to create these diagrams

Sequence diagrams represent an interaction among objects in the form of messages ordered in a sequence by time In a sequence diagram, you arrange objects across the x-axis You place the object that starts an interaction to the extreme left The objects that come later in the message sequence are placed to the right of the interaction-initiating object The messages sent and received by the objects in an interaction are placed along the y-axis in an increasing order of time

Creating Sequence Diagrams

The following figure depicts the arrangement of objects and messages in a sequence diagram

Arrangement of Messages and Objects in a Sequence Diagram

An object may be created or destroyed when an operation is performed You can use sequence diagrams to depict the creation and destruction of an object In addition,

sequence diagrams depict the change in the focus of control of an object in the form of a rectangular bar The length of rectangle bar represents the duration of time for which an object interacts with another object The following figure depicts a sequence diagram that shows how an object is created and destroyed, the focus of control, and the object lifeline

Focus of Control and Object Lifeline in a Sequence Diagram

In the preceding figure, Object1 creates Object2 and subsequently sends a message to it When Object2 completes its processing, it is destroyed

Consider the following sequence diagram for the Order Parts use case of the IMS system

Sequence Diagram for the Order Parts Use Case

In the preceding figure, the Inventory Manager creates an instance of the order class and invokes the issueOrder() method of the order class The order object stores the details in the Inventory Database When the details are stored in the database, the order object receives a Transaction Complete signal and is then destroyed

When an object invokes its own method or receives a callback from another object, a new focus of control is represented over the existing focus of control and is called a nested focus of control

Note

The following figure shows the nested focus of control of an object

Nested Focus of Control

Unlike sequence diagrams, communication diagrams do not depict the object lifeline

In a sequence diagram, the flow of control depicts a sequential flow of messages

However, a programming logic may require you to depict the iterations of messages or the branching of the flow of control Iterations are repetitions of messages You can use the following statement to depict an iteration in a sequence diagram:

*[ j := 1 n ]

You use an asterisk, *, to indicate that the message is being sent repeatedly You can depict iteration by using the following notations:

„ [j < 10]: Specifies that the message will be sent until the value of j is less than 10

„ [val not found]: Specifies that the message will be sent until val is found

The following sequence diagram depicts that the Math object requests the

numberProperties object to calculate if a number is prime or not, iteratively

Iteration in Sequence Diagrams

Branching of messages occurs when a set of messages responds to a call The message to

be sent is guarded by a condition, which is a Boolean expression If the condition

evaluates to true, then the first message is sent, otherwise, the second message is sent There is no specification on what type of conditions you may include in your interaction diagrams You can use either an English language expression or a programming language expression You can use the following English language expression to depict a condition: [ j less than zero ]

The following statement shows how you can use a programming language expression to write a condition:

[ j < = 0 ]

To depict the receipt of messages by an object, you can divide the object lifeline into branches The following figure shows how to divide an object lifeline into branches

Note

Branching the Object Lifeline

For example, in the IMS, the inventory manager checks the reorder level of an automobile spare part before placing an order If the reorder level condition is true, then the inventory manager places the order for the spare part If the reorder level condition is false, then the inventory manager checks the information about the last order for the spare part

The following diagram depicts the branching of the flow of control of the O1 object in the Place Order use case of the order processing system

The Sequence Diagram for the Order Parts Use Case

Messages in a sequence diagram may be sequenced by giving them a sequence number Messages can be given names that give a description of the message passing between

objects or can be mapped to a method of the called class

Store Order Details

<<Create>>

[qty<=CritialLevel]

issueExpressOrder(pcode, scode) issueOrder(pcode,scode) checkQty()

p1:

parts

Inventory Database

Note

The guidelines that you need to follow when you model a sequence diagram are:

„ Identify the collaboration for an interaction in the system, subsystem, and use cases

„ Identify the objects that have higher responsibility in the interaction To draw a sequence diagram, place the objects with high responsibility on one side and the low responsibility objects on the other

„ Identify the lifeline of each object in view of the control to depict the creation and destruction of an object

„ Identify the messages that flow between the lifeline of objects You also need to identify the properties of these messages to obtain information about the semantics of the interaction

„ Identify the preconditions and post conditions for each message to control the flow

of objects

Communication diagrams represent the interaction among objects in the form of

messages To draw a communication diagram, you identify the objects in collaboration and represent them as the vertices of a graph After you place the objects, you can draw straight lines that represent the links among these objects to connect the objects Note that objects send and receive messages across these links The dynamic aspect of an

interaction diagram can be depicted by messages that are passed among objects across links Therefore, communication diagrams depict the organization of objects in the

sequence of messages flowing between them The constituents of a communication diagram are organized in such a way that the related objects are closely placed The following figure shows a collaboration and the messages passed in the collaboration

A Communication Diagram with Messages

Unlike communication diagrams, sequence diagrams do not have paths that link

objects and messages arranged according to time

Creating Communication Diagrams

messageA

messageB

Collaboration of Objects

Object3 Object2

Object1

Note

You can number the messages in a communication diagram for sequencing and indicating their time order The sequence numbers are prefixed before the messages The following figure shows the path between two objects and messages with sequence numbers in a collaboration

Path among Objects and Sequenced Messages in a Collaboration

The following figure shows the objects, links, and sequence of messages among the various objects of the communication diagram for the use case, process order

Communication Diagram with Sequenced Messages

Sequence and collaboration diagrams are isomorphic This means that they contain the same information and can be derived from each other While sequence diagram depicts the time sequencing of messages, the communication diagram depicts structural

responsibilities of the participating objects

Sequence and communication diagrams are similar because of the fact that both represent collaboration and the messages flowing between the constituents of the collaboration You can also depict iterations and conditions in a communication diagram in the same way as in sequence diagrams You can derive a communication diagram from a sequence diagram by using the objects and messages of the sequence diagram Organize the objects

so that the related objects are placed together and place a sequence number before each

message in the communication diagram based on the time ordering depicted in the

sequence diagram

Similarly, you can derive a sequence diagram from a communication diagram by using the objects and messages of the communication diagram Place the objects and draw their respective object lifelines Draw the messages among objects according to the sequence specified in the communication diagrams

The guidelines that you need to follow when you model a communication diagram are:

„ Identify the collaboration that involves an interaction in the system, subsystem, and use cases

„ Identify the objects that have higher responsibility in the interaction Draw these objects on a graph so that the objects with high responsibility are placed on one side and the objects with lower responsibility are placed on the other

„ Identify the links among objects You need to place the association links to depict the relationship among objects

„ Identify all the messages that flow across the links established among objects

Assigning Responsibilities to Classes

You need to assign responsibilities to a class or a set of classes to ensure that the software system has the required functions to suit the requirement document

The decisions about responsibilities of classes are taken when interaction diagrams are created They include the decision to identify the methods that need to be invoked in one object by another object so that each instance of a class carries out its responsibilities A responsibility is implemented by using methods of classes, which may implement the entire responsibility or collaborate with the other methods to implement a responsibility Consider the IMS where you need to assign the responsibility of processing an order to a class or multiple classes The supplier class has the task to submit the order The

submitOrder() method of the supplier class has the task to deliver the order The order class stores the information about the parts accepted and rejected The order class accepts and evaluates the order received from the supplier The IMS database stores the

information about the order and the quantity of parts received and rejected The three collaborators for processing an order are supplier class, order class, and inventory database

The following figure depicts the communication diagram with the objects carrying out their responsibilities to process an order

Communication Diagram with Class Responsibilities

The guidelines that you need to follow when you assign responsibilities to objects are:

„ Assign responsibilities to classes such that they perform all the tasks that are performed by the real-world entity that the classes represent

„ Assign responsibilities to a class if the class has the attributes that will enable it to fulfill the responsibilities

„ Assign responsibilities to multiple classes if all the classes have the data to fulfill the responsibility

„ Distribute responsibilities evenly to the various classes of your software system

„ Check that all the classes of the software system have some responsibility assigned

to them If no responsibility is assigned to a class, you need to check whether the class is required

„ Check if too many or unrelated responsibilities have been assigned to a class If such

a class exists, split the class into smaller classes

Problem Statement

Janes Technology has been assigned the task of creating a dynamic model of the

prototype for the InfoSuper bank ATM system Janes Technology needs to implement only the cash withdrawal system in the prototype for the InfoSuper bank The following table describes the classes, attributes, and operations for the cash withdrawal feature of the InfoSuper bank, which the design team of Janes Technology has identified

Class Operations Description

ATM Show() Displays the location and

branch name of the ATM

GetPin() Accepts the PIN entered by the

customer and verifies it

GetAccount() Fetches the account

information based on the card_ID and PIN

ATMCard

SetPin(int) Updates the PIN

InsertCard() Prompts the customer to insert

the ATM card

SelectTransaction() Selects a transaction from a

list of transactions

EnterPin() Prompts the customer to enter

the PIN

ChangePin() Invokes the PIN change

request Enters the new PIN WithdrawCash() Invokes the cash withdrawal

operation

BankCustomer

RequestTransactionSummary() Requests for a transaction

summary

CalculateInterest() Calculates the interest for the

account This is an abstract operation

Class Operations Description

VerifyWithdrawalAmount() Verifies if the amount to be

withdrawn is less than the account balance amount

CurrentAccount CalculateInterest() Calculates the interest for the

ReadCard() Reads the Card_ID associated

with the ATM card

EjectCard() Ejects the ATM card

CardScanner

ValidatePIN() Validates the pin number

Prompt() Prompts the respective screen

according to the request

DisplayScreen

AcceptInput() Accepts the required input on

the displayed screen

SupplyCash() Supplies the verified amount

as cash

CashDispenser

GenerateReceipt() Generates a receipt for the

cash dispensed

The design team has also created the following class diagram after identifying the classes and operations for InfoSuper bank

Class Diagram for the Prototype of the InfoSuper Bank ATM System

Identify the activities that the development team needs to perform to model the dynamic view of the prototype

Prerequisite: To perform this activity, you will need the BANK_ATM.vsd file, which

you created in the activity “Modeling the Static View of the Bank ATM System” of Chapter 6

Solution

To model the dynamic view of the cash withdrawal feature of the ATM system, you need

to perform the following tasks:

1 Identify the collaboration and interactions

2 Create a sequence diagram

3 Create a communication diagram

Task 1: Identifying the Collaboration and Interactions

The following table lists the various classes that collaborate to realize the cash withdrawal feature

Class Responsibilities

BankCustomer Supply the PIN number

Select the type of transaction

Supply the amount to be withdrawn

CardScanner Accept and read the card information

Eject the card after the transaction is complete

DisplayScreen Prompt the user for input

ATMCard Verify the PIN number

Get the information about the customer’s account

Account Verify the PIN number

Get the information about the customer’s account

Verify the amount to be withdrawn

Update the amount in the account after the transaction

Transaction Starts a transaction

Get the cash balance from the account

CashDispenser Supply cash to the customer

Generate a receipt of the transaction

Class Responsibilities

The following figure depicts the sequence diagram for the cash withdrawal feature of the InfoSuper bank ATM system

Sequence Diagram for the InfoSuper Bank ATM System

The following figure depicts the communication diagram for the cash withdrawal feature

of the InfoSuper bank ATM system

Communication Diagram for the InfoSuper Bank ATM System

Task 2: Creating a Sequence Diagram

To create a sequence diagram, you need to perform the following steps:

1 Select StartÆAll ProgramsÆMicrosoft OfficeÆMicrosoft Office Visio for

Enterprise Architects.

2 Open the Bank_ATM Visio file The Bank ATM model appears

3 Right-click the Iteration2 folder in the Model Explorer window, and select

NewÆSequence Diagram The Sequence-1 tab with a blank drawing page appears

4 Drag the Object Lifeline symbol ( ) from the UML Sequence (Metric) stencil

on the drawing page

5 Double-click the Object Lifeline symbol to set its properties The UML Classifer

Role Properties dialog box appears

6 Type CS in the Name text box

7 Select Iteration2::CardScanner from the Classifier drop-down list, as shown in the

following figure

UML Classifier Role Properties

8 Click the OK button The following figure shows the object lifeline symbol for the

CardScanner class

Object Lifeline Symbol for CardScanner Class

9 Right-click the Object Lifeline symbol and click the Shape Display Options option The UML Shape Display Options dialog box appears

10 Select the Classifier name check box in General options section

11 Click the OK button The lifeline symbol appears as shown in the following figure

Object Lifeline Symbol Displaying the Classifier Name

12 Similarly, draw the object lifeline symbols for the following classes: