Use Case Analysis From soft systems methodology to understanding the system functionality.
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Transcript of Use Case Analysis From soft systems methodology to understanding the system functionality.
Use Case AnalysisUse Case Analysis
From soft systems methodology to understanding the system functionality
The VisionThe Vision
SSM Models
Use Cases
Activity Models
Dynamic Models
ObjectModels
Programs
Databases
BusinessComputing
Beginnings of a MethodBeginnings of a Method
Soft Systems
Model
Use Case ModelsUse Case Models
• Consist of
– Use Cases
– Actors
– Relationships between Actors and Use Cases
What is a Use Case?What is a Use Case?
Formal definition
“A Use Case is a sequence of transactions performed “A Use Case is a sequence of transactions performed
by a system that yields a measurable result of values by a system that yields a measurable result of values
for an actor”for an actor”
A Use Case:
• is a meaningful piece of system functionality
• models a dialogue between a user and the systemNote - The user can be another system
• is more than a simple transaction (e.g. enter customer
address)
We draw a use case as:We draw a use case as:
A Use Case
Examples of Use CasesExamples of Use Cases
• Print Invoice
• Correct Invoice
• Chase Payment
• Register Bad Debt
What is an Actor?What is an Actor?
• Anyone or any thing that uses or interfaces with the
system, such as:
– customer
– credit controller
– EPOS system
– Bank system
We draw actors as:We draw actors as:
An Actor
Actors and Use CasesActors and Use Cases
• An Actor may use many Use Cases
• A Use Case may interface with many Actors
• We draw a simple line to indicate interaction
Relationships between actors and Relationships between actors and use casesuse cases
An ActorA Use Case
Arrows indicate who initiates Arrows indicate who initiates interactioninteraction
An ActorA Use Case
Sometimes the use case initiates interaction
Use Cases can be relatedUse Cases can be related
• One Use Case may use another Use Case
• Sometimes that use is an exception or
alternative, and we say that one Use Case
extends another Use Case
StereotypesStereotypes
UML has a concept called a stereotype which is used to describe the type of relation ship that is being used.
Stereotypes are written between guillemets << >> (pronounced “ gweemays”) which are placed on the relationship lines.
Example
<<extend>>
ExtendExtend relationship relationship
Used where an alternative or an exception is being shown.
In this case as part of a money collecting function, it is required that a warning letter is sent out.
Note the direction of the arrow. It always goes from the extension to the base case.
Chase Payment Issue Warning Letter
<<extend>>
IncludeInclude relationship relationship
When use cases share the same piece of functionality,
we use the include relationship whereby the common
use case is linked to the use cases that use its
functionality.
In this case, the Validate User
use case needs
to be used for taking
an order and for
displaying user
information
Note direction is from base to extension case
Take order
Confirm details
Validate user
<<include>>
<<include>>
SSM Conceptual ModelSSM Conceptual Model
enrol studentsdesign
educationprogrammes
appreciatenational
standards
educatestudents
allotresources
designand carry outassessment
awarddegrees + diplomasto students reaching
acceptable levels
Any use cases here?
Initial thoughts on a development Initial thoughts on a development methodmethod
Problem SituationProblem Situation
• Student Retention
• Too many students enrol on a course then withdraw in their first year
• Need a software system to help solve the problem– An improved
school intranet
Identify Relevant SystemsIdentify Relevant Systems
1. Admissions
2. Pastoral Care
3. Timetabling
4. Module Delivery
5. Peer Tutoring
6. Assessment
7. Attendance Monitoring
8. Research
Definition of a Pastoral Services Definition of a Pastoral Services SystemSystem
• A system under the control of an in-school counselling team – giving appropriate referrals to external agencies to students presenting personal problems to members of the counselling team.
Root Definition for Peer-TutoringRoot Definition for Peer-Tutoring
• A system owned by the school that provides study skills support to students using volunteers from the student body with the quality of their support activities monitored by academic staff
Conceptual ModelConceptual Model
Identify suitable peer tutors
Document Skills of peer tutors
Train peer tutors
Advertise
Receive tutee
Document tutee needs
Book times and rooms
Attendance MonitoringAttendance Monitoring
Record absentees during a tutorial session
Know tutorial group members
Inform pathway leader of persistent absentees
Know student's pathway leader
Inform student of contact with pathway leader
Related Use CasesRelated Use Cases
Print Class List
Enter Attendance Data for Class Tutorial
Print Attendance Record for Specific Class
Print Attendance Record for Specific Student
Module Leaderemail pathway leader and student
Let’s consider this one
Create Class ListCreate Class List
The information displayed here might be brought The information displayed here might be brought together through collaboration between objectstogether through collaboration between objects
: Pathway : Module : StudentCreate Class List Form
CreateClassList( )getStudentDetails( )
getPathwayTitle( )
Class Diagram showing relationships between Class Diagram showing relationships between these objectsthese objects
Module
NameModule Code
Create Class List()
Student
Name
get student details()n nn n
enrolled on
Pathway
TitleDescription
get pathway title()1
nn
1
registered on
We can do two things with this class We can do two things with this class diagramdiagram
• Implement it in an OOPL
• Translate it into an entity model then implement the entity model as a relational database
We’ve considered how class diagrams We’ve considered how class diagrams can be implemented in an OOPLcan be implemented in an OOPL
Pathway
Title
Student
Name
1
n
1
n
Module
CodeTitle
nn
n
n
n
n
And how class diagrams can drive And how class diagrams can drive database designdatabase design
• When the computer is switched off…. – …the data used by the class diagram must be stored in a
database
My Next Example ProgramMy Next Example Program
Another StudentAnother Student
The Underlying DatabaseThe Underlying Database
The Program that uses the The Program that uses the DatabaseDatabase
The Class DiagramThe Class Diagram
Group
Student
n
Module Work Recordn1
n
n1
System Boundary
Group Student
Get Group Student Numbers
Get Student Number
System Boundary
Group Student Module Results
Get Student Marks
Get Module Results
Three TiersThree Tiers
Group
Student
n
Module Work Recordn1
n
n1
An interface developed in Visual Basic or HTML?
An implementation of the class diagram using VB class modules or Java?
An implementation of the entity model in MS Access, ORACLE, MySQL?
Classic Three Tier ArchitectureClassic Three Tier Architecture
Back to Use CasesBack to Use Cases
Finding Use Cases Finding Use Cases (cont’d)(cont’d)
• Examine all the activities in the conceptual model and determine where the system is used
• Big use cases sometimes naturally break down via includes and extends
• Elaborating the use case often finds other use cases
Finding Use Cases Finding Use Cases (cont’d)(cont’d)
To fulfil a defined role:
• What do users need to be able to do?
• What are users trying to accomplish
• What are the main tasks of users in this role?
• What information do users in this role need to examine, create, or change?
• What do users in this role need to be informed of by the system?
• What do users in this role need to inform the system about?
What do Students do?What do Students do?
• Enroll in, attend, drop, fail, and pass modules.
• Need a list of available modules.
• Need to determine basic information about a module, such as its description and its prerequisites.
• Obtain a copy of their transcript, their course schedules, and the fees due.
• Pay fees, pay late charges, receive reimbursements for dropped and cancelled modules, receive grants, and receive student loans.
• Graduate from a school or drop out of it.
• Need to be informed of changes in modules, including room changes, time changes, etc.
Prototyping and Use CasesPrototyping and Use Cases
• Interface prototypes are good for:
– Agreeing user interaction (HCI factors)
– Clarifying with users
– Determining data requirements
– Working out how to group use cases in interfaces
Use Case ProformaUse Case Proforma
• Number and Name
• Primary Path
• Pre- and post-conditions
• Alternatives and Exceptions
• Related Use Cases
• Prototype Interfaces
• Activity Diagrams
• Supported Business Processes / Activities
• Notes
A Use Case CatalogueA Use Case Catalogue
• Is a Substantial Document
• Overviewed by set of Use Case Diagrams
• Has Individual Use Cases
• Linked into CASE tool
• This is your requirements definition!
Invoicing use case (1)Invoicing use case (1)
Use Case Number: 99
Use Case Name: Invoice Customer
Brief Description: This is run daily to send invoices to customers. Itemsthat have been delivered are billed all on the same invoice. Customersare only billed once a month.Actors: Daily batch run, customer (indirectly, through post)Frequency of Execution: DailyScalability: Only one instance of this runs at any one time.Criticality: Essential. Every days delay to printing invoices affects thebank balance considerably. Not running this for 7 days could trigger aserious cash flow problem.Primary Path:The following sequence is carried out for every customer on the salesledger who has not been billed in the last month:
1. Get sales items from the sales ledger.2. Get customer details from the customer file, covering billing addressdetails.3. Get any credits that the customer has.4. Get discount details for customer.5. Print the invoice header6. Print the line items on the invoice7. Calculate any discounts8. Apply any credits9. Calculate and print the invoice total10. Calculate and print the VAT11. Mark items on sales ledger as invoiced
Invoicing use case (2)Invoicing use case (2)
Use Cases Related to Primary Path: Alternatives:2.1 No customer details on customer file, so print an error message on areport. Do not mark the items on the sales ledger as invoiced. Themessage needs to detail the sales items that have been entered.Use Cases Related to Alternatives:Invoicing error reportExceptions: Use Cases Related to Exceptions: Notes:
Why Use Case Modelling?Why Use Case Modelling?
• Agree system functionality and scope
• Relate it to how business processes are supported
• High level soft model, can be understood by all parties
• Prioritise implementation - particularly important for
iterative development
What about Objects?What about Objects?
• You don’t need to be developing an OO system to use
Use Case analysis
• Once you have Use Cases, then OO analysis and
design can begin in earnest
SummarySummary
• Use Cases are meaningful chunks of system
functionality
• They support business processes
• They are important for defining and agreeing scope of a
system
• They can be prototyped
• They are important for driving implementation
schedules
• Modern development methods are “use case centric”