Week 10

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Sequence Diagrams

Outline

a) Add scenarios to the system to describe how Use Cases are realized as interactions among societies of objects

b) Describe a scenario by applying sequence diagramsc) Draw Sequence diagrams for given case studies

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Sequence Diagram • Sequence diagram represents the dynamic

interaction between objects, or between actors and objects ordered in time.

• A sequence diagram is composed of a timeline, objects that interact across this timeline, and the messages that they exchange.

• Represent a scenario in the system

Major Ingredients of a Sequence Diagram

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: Patient

aPatient :Patient

1: enquiresAvailability

Patient ChecksAvailability of Doctor

The Actor

Object

Time Line

Message

Self Message

Focus of Control

Steps in the Sequence

NotesT his is an

explanatory note

How do you start?

1. Identify the process/algorithm/activity you want to capture( may be a use case)

2. Identify the major objects involved 3. Map out the flow of control/ messages to

achieve the result

Relating Sequence Diagrams to Class Diagrams

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aPatient: Patient

1: checkPatientDetails( )

Patient

checkPatientDetails( )

Objects on Sequence Diagrams belong to Classes in Class Diagram

Messages on Sequence Diagrams come from Methods available to the Class on Class Diagrams

A Layered Architecture

• Subsystems are shown as UML packages linked by dependencies

• A dependency without a stereotype means uses

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Advancing the Sequence Diagrams from Analysis to Design: Showing specific objects

: ActorPatientaDoctor :

Doctor

checkAvailability( )

: ActorPatientSystem

checkAvailability()

(A)Analysis Sequence DiagramRead “System”

(B)Design Sequence DiagramShows “Doctor” – a Specific object

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Representing objects

Message between objects

More on messages

Indicating method calls

Lifetime of objects

Understanding Focus of Control and return message

aPatient : Patient

: Doctor

getSchedule( )

getAvailable( )

availability

Focus ofControl

ReturnProtocol

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Creating and Destroying an Object

: PatientForm

aPatient : Patient

bookConsultation( )

“Creating an Object”Shown with the arrow pointing directly to the Object

“Deleting an Object”Shown with a Cross on the Timeline

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Manage course information• The sequence of steps carried out in the "Manage course information" flow

are:• A user who is a course administrator invokes the manage course

functionality. • The manage course functionality of the course administrator invokes either

the course creation or course modification functionality of a course. • After the course is either created or modified, the manage topic

functionality of the course administrator calls the topic creation or modification functionality of a topic.

• Finally, the user invokes the assign tutor to course functionality of the course administrator to assign a tutor to the selected course.

• Now, let us model these steps into a Sequence diagram for the "Manage course information" functionality.

• the following use cases for the Courseware Management System were defined:– View courses – Manage topics for a course – Manage course information – View course calendar – View tutors – Manage tutor information – Assign courses to tutors

• Sketch a sequence diagram for the “normal” operation of an ATM (i.e. a customer inserts the card, enters his/her PIN, enters the amount, takes the card, and takes the money). The sequence diagram should show the interaction between the different components of the ATM. The ATM consists of the following components:

• • screen • keyboard • card reader • money tray • money output device • interface to banking server (for modifications of the account data of the

customer)•

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Use Case: Have Dinner

Scope: Restaurant

Primary Actor: Customer

Normal Flow: 1. Customer is seated at a table2. Customer asks the waiter for the menu.3. Customer orders drink(s).4. Customer orders appetizer(s).5. Customer orders main course(s).6. Customer orders dessert(s).7. Customer asks for the bill.8. Customer pays the bill and receives change (if any).

Alternate Flow / Exceptions:

1.aCustomer asks the waiter for his or her name.

Restaurant Example

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A sequence diagram fragment that contain an alternative combination fragment

28A sequence diagram with a loop combination fragment

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Make AppointmentUse Case-Analysis

Normal Flow: 1. Appointment clerk verifies that the needed medical service is provided by the hospital.

2. Appointment clerk records patient’s personal and contact data.

3. Appointment clerk records information about the referral source.

4. Appointment clerk consults hospital’s schedule to find a free slot for the required medical service.

5. Appointment clerk verifies that the patient is available for the appointment.

Loop 1: Repeat steps 4-5 until hospital’s schedule matches patient’s availability.

6. Appointment clerk makes the appointment. Loop 2: Repeat steps 4-6 for each appointment.

Alternate Flow/ Exceptions:

2.a Patient is not on file. Create new patient. (Extend: 141 - Create Patient.)

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UML Extension Mechanisms • UML offers a set of mechanisms that

allow modeling to be refined, extended and adapted to specific needs.

• Stereotyping is the specialization of standard UML notations.

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UML Stereotyping

• UML stereotyping is typically simple but powerful: If any building block of UML is not specialized enough to express your specific needs, you may specialize it yourself by specifying a tag and/or assigning an icon.

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END