System Analysis Lab (Week 3)

7/27/2019 System Analysis Lab (Week 3)

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13CSIS01I System Analysis and Design

Lab 2

Use Case Diagrams

What is a Use Case Diagram?

A use case diagramis a behavioralUML diagram used to describe the user's interactionwith a system. The diagram includes actors (users) and their goals (use cases), and any

dependencies among those goals. It is a high-level description of a system's

functionalities.

A use case diagram can have many different types of users, and a single diagram can

represent the various ways each of them interacts with the system.

A use case, on the other hand, is a textual description explaining the sequence of events

and main functionalities that is then drawn as a use case diagram. Below is an example

of a use case:

Use Case

ElementDescription

Use Case

NumberID to represent your use case

Application What system or application does this pertain to

Use Case

NameThe name of your use case, keep it short and sweet

Use Case

DescriptionElaborate more on the name, in paragraph form.


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Primary Actor Who is the main actor that this use case represents

Precondition What preconditions must be met before this use case can start

Trigger What event triggers this use case

Basic Flow

The basic flow should be the events of the use case when everything

is perfect; there are no errors, no exceptions. This is the "happy day

scenario". The exceptions will be handled in the "Alternate Flows"

section.

Alternate

FlowsThe most significant alternatives and exceptions

How do we draw use cases?

Symbols used:

The Actor:the person who uses a functionality of the system. They are represented as a

simple stick figure.

The Use Case/Functionality: what the system's user wants to accomplish. It is

represented as short texta few words at mostwithin an oval-shaped bubble.

The Line Segment:a simple, arrow-less line that connects the actor to the use case.

The Uses Arrow:this arrow is drawn to indicate that, for example, action X must involve

doing action Y at least once. In other words, Y is a small action that is part of the larger

action, X.

The example below is a top-level use case diagram depicting a ticket clerk in an airline

reservation system. S/he checks in passengers, and adds or cancels reservations.


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Now, if we wish to add more information about each of those three functionalities, we

will draw another use case to follow up on the one above.


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The Extends Arrow:is drawn to indicate that action Y is a special case behavior of the same type

as the more general action, X.

For example, airline passengers may prefer one type of seating over the other, but since theirpreference will not always be available, the seat they want must be checked for availability.

Although the process of checking for window seats or aisle seats is slightly different, they are

still very similar. Hence in the use case diagram, they are depicted as different actions, but

extend a common, generic process called 'assigning seats'.


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Exercises

Use Case #1:

Use Case

ElementDescription

Use Case

Number1

Application Bank System

Use Case

NameCustomer makes an ATM transaction

Use Case

Description

A bank customer wishes to make a quick transaction using one of

their bank's ATMs instead of going to the actual bank location.

Primary Actor Bank customer, Bank

Precondition Bank customer must have a valid ATM card

Trigger N/A

Basic Flow

The customer finds an ATM and inserts their card into the slot. They

login using their secret number, and proceed to choose a transaction.

They can withdraw cash, deposit cash, check their bank balance, or

print a receipt.

Alternate

Flows

When the customers enters their secret number, it is false

When the customer enters their ATM card, the machine fails to

read it


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Use Case #2:

Use Case

Element

Description

Use Case

Number2

Application Airline Reservation System

Use Case

NameCheck in Incoming Passengers

Use CaseDescription

The ticket clerk checks in passengers coming to board a flight.

Primary Actor Ticket Clerk

Precondition Passengers already have their complete travel documents

Trigger N/A

Basic Flow

Every time a passenger moves up to the ticket clerk's window, they

must have their luggage weighed, and assigned a seat on the plane.

The ticket clerk will take the passenger's seating preference into

consideration, and search according to whether the passenger prefers

a window seat, or an aisle seat.

Alternate

FlowsThe ticket clerk tries to assign a seat, only to find there are none


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References:

Use Case Examples Effective Examples and Tips. D, Levy. June 12, 2013. Retrieved from

URL:http://www.gatherspace.com/static/use_case_example.html

UML Use Case Diagrams: Tips and FAQ.Retrieved from URL:

http://www.andrew.cmu.edu/course/90-754/umlucdfaq.html
http://www.gatherspace.com/static/use_case_example.htmlhttp://www.gatherspace.com/static/use_case_example.htmlhttp://www.gatherspace.com/static/use_case_example.htmlhttp://www.andrew.cmu.edu/course/90-754/umlucdfaq.htmlhttp://www.andrew.cmu.edu/course/90-754/umlucdfaq.htmlhttp://www.andrew.cmu.edu/course/90-754/umlucdfaq.htmlhttp://www.gatherspace.com/static/use_case_example.html

System Analysis Lab (Week 3)

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