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<!DOCTYPE html>
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<div id="header_main">
<pre
class="myDiv"
><h2><b>VIRTUAL LABS: SOFTWARE ENGINEERING - FUNCTIONAL USE CASES</b></h2></pre>
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<h2 style="color:red">Objectives</h2>
<ul>
After completing this experiment you will be able to:
<li>
How to identify different actors and use cases from a given
problem statement
</li>
<li>
How to associate use cases with different types of relationships
</li>
<li>How to draw a use-case diagram</li>
</ul>
<h2 style="color:red">Time Required</h2>
<p>Around <b>3.00 </b>hours</p>
<h2 style="color:red">Use case diagrams</h2>
<p>
Use case diagrams belong to the category of behavioural diagram of
UML diagrams. Use case diagrams aim to present a graphical overview
of the functionality provided by the system. It consists of a set of
actions (referred to as use cases) that the concerned system can
perform, one or more actors, and dependencies among them.
</p>
<h4 style="color:blue">Actor</h4>
<p>
An actor can be defined as an object or set of objects, external to
the system, which interacts with the system to get some meaningful
work done. Actors could be human, devices, or even other systems.
For example, consider the case where a customer withdraws cash from
an ATM. Here, customer is a human actor.
</p>
<ul>
Actors can be classified as below:
<li>
<b>Primary actor:</b> They are principal users of the system, who
fulfill their goal by availing some service from the system. For
example, a customer uses an ATM to withdraw cash when he needs it.
A customer is the primary actor here.
</li>
<li>
<b>Supporting actor:</b> They render some kind of service to the
system. "Bank representatives", who replenishes the stock of cash,
is such an example. It may be noted that replenishing stock of
cash in an ATM is not the prime functionality of an ATM.
</li>
</ul>
<p>
In a use case diagram primary actors are usually drawn on the top
left side of the diagram.
</p>
<h4 style="color:blue">Use Case</h4>
<p>
A use case is simply a functionality provided by a system.
Continuing with the example of the ATM, withdraw cash is a
functionality t hat the ATM provides. Therefore, this is a use case.
Other possible use cases includes, check balance, change PIN, and so
on. Use cases include both successful and unsuccessful s cenarios of
user interactions with the system. For example, authentication of a
customer by the ATM would fail if he enters wrong PIN. In such case,
an error message is displayed on the screen of the ATM.
</p>
<h4 style="color:blue">Subject</h4>
<p>
Subject is simply the system under consideration. Use cases apply to
a subject. For example, an ATM is a subject, having multiple use
cases, and multiple actors interact with it. However, one should be
careful of external systems interacting with the subject as actors.
</p>
<h2 style="color:red">Graphical Representation</h2>
<p>
An actor is represented by a stick figure and name of the actor is
written below it. A use case is depicted by an ellipse and name of
the use case is written inside it. The subject is shown by drawing a
rectangle. Label for the system could be put inside it. Use cases
are drawn inside the rectangle, and actors are drawn outside the
rectangle, as shown in figure - 01.
</p>
<img
src="https://cdn.glitch.com/4c13ff70-b984-4f5b-aef6-64e38ef0e78b%2Fgr.png?v=1604957732563"
/>
<p>
Figure - 01: A use case diagram for a book store
</p>
<br />
<h2 style="color:red">Association between Actors and Use Cases</h2>
<p>
A use case is triggered by an actor. Actors and use cases are
connected through binary associations indicating that the two
communicates through message passing. An actor must be associated
with at least one use case. Similarly, a given use case must be
associated with at least ne actor. Association among the actors are
usually not shown. However, one can depict the class hierarchy among
actors.
</p>
<br />
<h2 style="color:red">Use Case Relationships</h2>
<ul>
Three types of relationships exist among use cases:
<li>
Include relationship
</li>
<li>
Extend relationship
</li>
<li>
Use case generalization
</li>
</ul>
<br />
<h4 style="color:blue">Include Relationship</h4>
<p>
Include relationships are used to depict common behaviour that are
shared by multiple use cases. This could be considered analogous to
writing functions in a program in order to avoid repetition of
writing the same code. Such a function would be called from
different points within the program.
</p>
<h5 style="color:green">
Example
</h5>
<p>
For example, consider an email application. A user can send a new
mail, reply to an email he has received, or forward an email.
However, in each of these three cases, the user must be logged in to
perform those actions. Thus, we could have a login use case, which
is included by compose mail, reply, and forward email use cases. The
relationship is shown in figure - 02.
</p>
<img
src="https://cdn.glitch.com/4c13ff70-b984-4f5b-aef6-64e38ef0e78b%2Fr.png?v=1604957729590"
/>
<p>
Figure - 01: A use case diagram for a book store
</p>
<h5 style="color:green">
Notation
</h5>
<p>
Include relationship is depicted by a dashed arrow with a «include»
stereotype from the including use case to the included use case.
</p>
<h4 style="color:blue">Extend Relationship</h4>
<p>
Use case extensions are used used to depict any variation to an
existing use case. They are used to the specify the changes required
when any assumption made by the existing use case becomes false.
</p>
<h5 style="color:green">
Example
</h5>
<p>
Let's consider an online bookstore. The system allows an
authenticated user to buy selected book(s). While the order is being
placed, the system also allows to specify any special shipping
instructions [vii], for example, call the customer before delivery.
This Shipping Instructions step is optional, and not a part of the
main Place Order use case. Figure - 03 depicts such relationship.
</p>
<img
src="https://cdn.glitch.com/4c13ff70-b984-4f5b-aef6-64e38ef0e78b%2Fer.png?v=1604957725220"
/>
<p>
Figure - 03: Extend relationship between use cases
</p>
<h5 style="color:green">
Notation
</h5>
<p>
Extend relationship is depicted by a dashed arrow with a «extend»
stereotype from the extending use case to the extended use case
</p>
<h4 style="color:blue">Generalization Relationship</h4>
<p>
Generalization relationship are used to represent the inheritance
between use cases. A derived use case specializes
some functionality it has already inherited from the base use case.
</p>
<h5 style="color:green">
Example
</h5>
<p>
To illustrate this, consider a graphical application that allows
users to draw polygons. We could have a use case draw polygon. Now,
rectangle is a particular instance of polygon having four sides
at right angles to each other. So, the use case draw rectangle
inherits the properties of the use case draw polygon and overrides
it's drawing method. This is an example of generalization relationship.
Similarly, a generalization relationship exists
between draw rectangle and draw square use cases. The relationship has
been illustrated in figure - 04
</p>
<img
src="https://cdn.glitch.com/4c13ff70-b984-4f5b-aef6-64e38ef0e78b%2Fgenr.png?v=1604957723544"
/>
<p>
Figure - 04: Generalization relationship among use cases </p>
<h5 style="color:green">
Notation
</h5>
<p>
Generalization relationship is depicted by a solid arrow
from the specialized (derived) use case to the more g
eneralized (base) use case.
</p>
<h2 style="color:red">Identifying Actors</h2>
<ul>
Given a problem statement, the actors could be identified by asking
the following questions [2]:
<li>
Who gets most of the benefits from the system? (The answer would
lead to the identification of the primary actor)
</li>
<li>
Who keeps the system working? (This will help to identify a list
of potential users)
</li>
<li>
What other software / hardware does the system interact with?
</li>
<li>
Any interface (interaction) between the concerned system and any
other system?
</li>
</ul>
<br />
<h2 style="color:red">Identifying Use cases</h2>
<p>
Once the primary and secondary actors have been identified, we have
to find out their goals i.e. what are the functionality they can
obtain from the system. Any use case name should start with a verb
like, "Check balance".
</p>
<br />
<h2 style="color:red">Guidelines for drawing Use Case diagrams</h2>
<ul>
Following general guidelines could be kept in mind while trying to
draw a use case diagram [1]:
<li>
Determine the system boundary
</li>
<li>
Ensure that individual actors have well-defined purpose
</li>
<li>
Use cases identified should let some meaningful work done by the
actors
</li>
<li>
Associate the actors and use cases -- there shouldn't be any actor
or use case floating without any connection
</li>
<li>
Use include relationship to encapsulate common behaviour among use
cases , if any
</li>
</ul>
<br />
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<p><i class="fa fa-home mr-3"></i>Anchal Soni(2020201099)</p>
<p><i class="fa fa-phone mr-3"></i> Aayushi Nigam(202020145)</p>
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