1BTEC HNC Systems Support Castle College 2007/8

Systems Analysis

Lecture 8

UML

Use Case Modelling

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Lecture Objectives

At the end of this lecture you should be able to:

• Explain what UML is

• Understand Use Case Modelling and identify the components

• Draw a Use Case Model

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System Modelling• Producing a Logical View of the

System means:

• Producing graphical models which use non-technical language

• Representing the system at various stages of design/development

• Charting business processes, requirements and interactions

• Why?

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UML

• Unified Modelling Language

• Developed by Grandy Booch, Jim Rumbaugh and Ivar Jacobon at Rational Software

• Thought Shower:What is Unified Modelling Language and what is it used for? (p.t.o)

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Some facts to help you• UML is just a syntax. It says nothing about

how to create a model

• UML is well documented byt little understood

• UML specifies 8 different diagrams. Not all are used in practise

• A use case diagram shows the functionality of the system from the ‘outside in’

• Class diagrams show the static structure of the system

Activity Time!

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UML Benefits

• Uses Object Oriented design concepts

• Is a popular method of visualising and documenting the software system

• Is independent of any specific programming language

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UML Benefits (cont.)

• Provides graphical tools, for example Use Case models

• Can represent the information systems from Users’ point of view

• Relate to Business standpoint

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Use case Diagrams

• One of the defined UML diagrams

• A Use Case Diagram visually represents the interaction between Users and the Information System

• During requirements modelling analysts and user together model the system functions

• Use Case diagrams can be drawn freehand, or using a Case Tool

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Use Case Diagram

In this diagram the Actor is a customer and the Use Case is a PIN number validation performed by the system

Customer

ATM System

Validate PIN

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Use Case Diagram (cont.)• The Use Case is the function that

the Actor (user of the system) wants the system to perform

• One Use Case is

– One complete use of the system from start to finish

– Performed by the System

• Represented: ellipse with a written name of the function

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Use Case Diagram (cont.)

• The Actor is:

– A person or system that directly interacts with the new system

– Represented by a stick figure

– External to the system – at the system interface

– The line joining the Actor and the Use Case is called an Association

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Use Case Diagram (cont.)• Stereotypes:

– Includes / Uses:One Use Case includes (uses the services of) another Use Case

– Extends: A Use Case that extends functionality

• There is a System Boundary which is illustrated by the square box in which the activities of the system take place

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Use Case Diagram (2)

Customer

ATM System

Get Balance

Validate PIN

<<Includes>>

How many use cases on Diagram? Name them

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Use Case Documentation

• It is always necessary to document diagrams in the modelling process

• Because:

– Analysts and designers work as a team (with each other and with Users, Managers, Testers, etc)

– A model alone can be subject to interpretation

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Use Case Descriptor

Name of Use Case: Validate PIN

Actor: Customer

Description: Verify bank card (including type) and validate PIN number entered by the actor

Successful completion: 1. User inserts bank card2. System Verifies bank card checks type and prompts user for PIN number3. User enters PIN4. System validates PIN and presents options menu to user5a. User cancels transaction and retrieves bank card

or5b. User selects another transaction

Alternative: 1. User inserts bank card2. System Verifies bank card checks type and prompts user for PIN number3. User enters PIN4. System validates PIN and finds it incorrect; system prompts user to re-enter PIN (Repeat

twice)5. User re-enters PIN6. System validates PIN and finds it incorrect (after 3rd attempt), retains card and informs user

Pre-conditions: ATM is on and functional

Post-conditions: PIN number entered has been validated as correct for the card used

Assumptions: None

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Use Case functions• Successful completion: the activities that

make up the functions of the Use Case

• Notice that the three activities consist of an Input, a Process and an Output

• Use the format:

– The user…

– The system…

– The user…

– The system…

Ensures a cleaner design

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Events Table: hotel booking

• Event: Customer makes booking

• Trigger: Customer Enquiry

• Source: CustomerActor: Hotel Clerk

• Activity (Use Case): Create new booking

• Response: Room booking confirmation

• Destination: Hotel Clerk and Customer

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Events tables to Use Case diagrams

We can use the Events table to define the elements of a Use Case model

Question: How does this work?

Answer : Our Events table has given us a Use Case -Create new booking

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Recap on Use Case model elements

The symbols we can use are as follows:

Actor

Association

Use CaseUse Case label

<<includes>>

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Actors and Use Cases

Our Event table tells there are 2 Actors or ‘Inter-actors’ involved with the system for the first event

Only the Booking Clerk interacts directly with the system

1. The Booking Clerk

2. The customer (who provides the trigger and necessary input information)

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Use Case model of the event

Remember this is just a fragment!

Hotel System

Create New Booking

Clerk

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Over to you…

• It is now your turn to complete the Hotel occurrences example

• Complete the table, and then translate it into a Use Case diagram

• Remember that practice makes perfect

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Answers

1. Customer contacts the hotel for a free room

2. Clerk checks room availability

3. Customer gives name and address

4. Customer pays deposit

5. Clerk updates system to show room booked

6. Customer rings to order flowers

7. Customer turns up

8. Clerk find room number and gives key

9. Clerk records room as occupied

10. Customer leaves

11. Bill calculated

12. Customer pays bill

13. Clerk records room empty and customer paid.

Customer Makes Booking

Customer Orders service

Customer Checks in

Customer Checks out

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Events & Use Cases Practise

Could you also construct an events table and Use Case diagram from this example?

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Summary

You should now be able to:

• Explain what UML is

• Understand Use Case Modelling and identify the components

• Draw a Use Case Model

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References• Systems Analysis & Design Shelley

Cashman and Rosenblat 6th Ed. Thomson (2006)

• Eva and Skidmore (2004). Introducing Systems Development. Palgrave Macmillan

• Satzinger JW, Jackson RB and Burd SD (2004). Systems Analysis and Design in a Changing World. 3rd edition. Thomson