requirements-modelling-1234885087533724-3

UML SIG – UML Lecture Series Requirements Modeling

UML SIG

UML Lecture Series

UML SIG

Requirements Modeling (Use Case Diagram +

Use Case Description)

UML Lecture Series

Requirements Modeling (Use Case Diagram +

Use Case Description)

UML SIG – UML Lecture Series Requirements Modeling Slide 2 (of 48)

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Session Objectives

At the end of this lecture You will be able to :

1. Draw a use case diagram to depict functional

requirements of a system.

2. Expose typical mistakes by students.

3. Write use case description for a use case.


UML SIG

• use case• use case diagram• functional requirements• non-functional requirements• actor• include• extend• use case specification/definition/description• flow of events• alternate flow of events / alternate pathway• exception flow of events / exception pathway• basic flow of events / happy pathway• non-functional requirements / shadow use cases

Keywords used in this lecture


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Thoughts to Ponder …

To my knowledge, no other software engineering language construct as significant as use cases has

been adopted so quickly and so widely among practitioners. I believe this is because use cases play

a role in so many different aspects of software engineering.

Ivar JacobsonFounding Father of UML and Creator of Use Case Diagram


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Functional vs. Non-Functional

Requirements

Functional

Non-Functional

Functional requirement are user ‘visible’ features and aretypically initiated by stakeholders of the system – generate report, login, etc.

Non-functional requirements are ‘non-visible’ features and but required for a effective running of an application – security, backup, etc.


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Session Objectives







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Use Case Diagram

Definition:A diagram that shows a set of use cases and actors and their relationships.

Use cases represent system functionality, the requirements of the system from the user’s perspective.


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Notations

use case A description of a set of sequences of actions, including variants, that system performs that yields an observable value to an actor. actorThe people or systems that provide or receive information from the system; they are among the stakeholders of a system.includeSpecifies that the source use case explicitly incorporates the behaviour of another use case at a location specified by the sourceextend Specifies that the target use case extends the behaviour of the source.

<<include>>

<<extend>>


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Actors

Actors

Could be human beings, other systems, timers and clocks or hardware devices.

Actors that stimulate the system and are the initiators of events are called primary actors (active)Actors that only receive stimuli from the system are called secondary actors (passive)


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Actors

Actors

Who/what will be interested in the system?

Who/what will want to change the data in the system?

Who/what will want to interface with the system?

Who/what will want information from the system?


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Use Case Diagram– Guidelines & Caution

1. Use cases should ideally begin with a verb – i.e generate report. Use cases should NOT be open ended – i.e Register

(instead should be named as Register New User)

2. Avoid showing communication between actors.

3. Actors should be named as singular. i.e student and NOT students. NO names should be used – i.e John, Sam, etc.

4. Do NOT show behaviour in a use case diagram; instead only depict only system functionality.

5. Use case diagram does not show sequence – unlike DFDs.


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Example – Include and Extend


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The use of include and extend is discouraged simply becausethey add unnecessary complexity to a Use Case diagram.

Since the primary purpose of use cases is to show usercentred functionality, the precedence of use cases takeslittle importance.

Include and Extend


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Quiz 1

Customer Service Clerk

Maintain Relationships

Order Clerk

Process Orders

CustomerMaintain Orders

SupplierMaintain Inventory

Packaging ClerkShip Product

Bill ing Clerk

Generate Invoice

Accounting System

Manager

Time

Decision Support


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Quiz 2


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Granularity of Use Cases

Add referenc

e

Remove reference

Search for reference

User

List references


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Granularity of Use Cases

Manage Reference

User

Generally, a use case should embody sufficient levels of granularity without which the use case may not be rendered as useful.


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Session Objectives







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Mistake 1


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Mistake 2


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Mistake 3


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Mistake 4


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Mistake 5


UML SIG Inventory System

In order to generate an invoice a clerk must log in. If a clerk is a first time user, one must have themselves registered. There should be an option for a user to register oneself within the login page. Any user can use the system to view products online.The option of login is also provided when a user views products online.

Discussion Exercise

Draw a use case diagram for the scenario below:


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Exercise - Solution


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Session Objectives







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Use Case Specification



Process Orders

Order Clerk

Maintain OrdersCustomer

Maintain Inventory Supplier

Ship ProductPackaging

Clerk

Billing Clerk

Accounting System

Generate Invoice

ManagerDecision Support

Time


UML SIG




Process Orders

Order Clerk

Maintain OrdersCustomer

Maintain Inventory Supplier

Ship ProductPackaging

Clerk

Billing Clerk

Accounting System

Generate Invoice

ManagerDecision Support

Time


UML SIG


Use case specification is synonymous to use case description

and use case definition and can used interchangeably.

Use case specification defines information that pertains to a

particular use case which is important in understanding the

purpose behind the use case.

Use case specification is written for every use case.

A use case specification has one or more flow of events or

pathways association with it.


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Flow of Events / Pathways

A flow of events or pathway is a textual description embodying

sequence of events with regards to the use case and is part of

the use case specification.

Flow of events is understood by the customer. A detailed

description is necessary so that one can better understand the

complexity that might be involved in realising the use cases.


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Flow of events describes how and when the use case starts

and ends, when the use case interacts with the actors, and the

information exchanged between an actor and the use case.

Flow of events is derived from a what perspective, NOT how

perspective. Hence, specific information like: interface details

and technical specifications should NOT be included in a use

case description.

Use case description serves as a ‘bridge’ between

stakeholders of a system and the development team.


UML SIG


Use case description serves as a ‘bridge’ between

stakeholders of a system and the development team.

Use Case Diagram

Use CaseSpecification

Programmers look at use case specification to understand complete requirements - SRS

Systems analyst produce usecase diagram & use case specification in consultation with end users


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Flow of Events

Describes how and when use casestarts and ends.

Does NOT describe user interface details.

Is generally a text-based file that is included under its use case in Rational Rose/Visual Paradigm


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Types Flow of Events / Pathways

Types of

Flow of Events

Basic Flow of Events@ Happy Path - is the most common pathway. It usually depicts a perfect situation, in which nothing goes wrong.

Alternate Flow of Events @ Alternate Pathway - is a pathway that is still considered a good pathway; it’s just not the most heavily travelled one

Exception Flow of Events @ Exception Pathways @ Unhappy Pathway – things don’t always go as planned. An exception is an error condition that is important enough to the application to capture.


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Types Flow of Events / Pathways

Basic Flow of Events@ Happy Path – You get to the ATM and successfully withdraw money

Alternate Flow of Events @ Alternate Pathway - You get to the ATM but could not withdraw money due to insufficient funds in your account.

Exception Flow of Events @ Exception Pathways @ Unhappy Pathway – You get to the ATM machine but your valid pin number is not accepted.


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See Example Word Document on Use Case Specification based on Remulak Productions

Use Case Specifications - Example


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Review Questions


UML SIGA use case specification cannot be done for an included use case.

True

False

Review Question


UML SIGUse case specification together with a use case diagram become part of what is know as system requirements specification (SRS)

True

False

Review Question


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Although non-functional requirements (i.e shadow use cases) are not “technically speaking” a use case, are still considered a use case to acknowledge the importance it has in the overall system.

True

False

Review Question


UML SIGBasic Flow of Events @ Happy Path is a series of events that happens some of the time

True

False

Review Question


UML SIGAlternate Flow of Events @ Alternate Pathway is a series of events that happens all the time

True

False

Review Question


UML SIGException Flow of Events @ Exception Pathway is a series of events that is impossible to happen.

True

False

Review Question


UML SIGBoth use case diagram and use case specification should not be too detailed.

True

False

Review Question


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Use Case Diagram - In Class Exercise

Write use case specification based on the case diagram for Inventory System.


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Summary

1. Use Case Diagram as a means to model functional requirements of a system.

2. Awareness of typical mistakes by students.



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Further Reading

http://download.boulder.ibm.com/ibmdl/pub/software/dw/rationaledge/jan03/UseCaseFAQS_TheRationalEdge_Jan2003.pdf

Use Case FAQs


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Reference

Jacobson I. 2003, “Use Case – Yesterday, Today and Tomorrow”, The Rational Edge, IBM

Documents

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