Use Case
Use Case - Summary Slide
 Use Cases – Definition
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The purpose of use cases
Why use use cases?
 UML - Use case diagram
 UML use cases – Actors
 Example of use case diagram
 Use case definition + description - the process
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Draw use case packages
Grouping of business functionality – Use case packages
 Draw use case diagrams
 Identify actors
 Complete verbal description
 Use cases – Verbal description
 Identify variants and exceptions
 Audit business process and term model
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Use Cases – Definition
A Use Case is a way of using a system
o A scenario that describes limited interaction
between a system and actors in the field
In a Use Case, you describe the use of a
system for a given work task
o You consider a complete work task, initiated by an
actor
o You utilise ”company language” in describing the
work task
o The aggregate Use Cases display the aggregate
actor use of the system
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The purpose of use cases
 The purpose for using use cases is to
o Uncover and describe all tasks that need doing in a system (of
both human and system actors)
o To analyse what functionality that need developing for the system
o The use of use cases must mean that the right functional
requirements are made of the IT system (the requirements of the
business!)
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Why use use cases?
 Use case strengths are
o That they work well as an analytical tool
o That the notation is simple and easy to pick up
o That they are easy to understand, both for the business and from the
technological aspect
o It is a widely recognised market standard
o That customer and supplier – or operators and technicians – can
jointly work out and understand the operational functionality
o They bring structure, and ensure complete analysis
 The challenge, then, is to find and describe all use cases!
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Use cases are documented in two ways
Use Case diagrams
o Give an overview of visible use scenarios in the
system
o Describes what actors that interact with the system
o Describes any linkages between use cases
Verbal description
o Describes the content of each use case
o Typically uses a pre-defined template
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UML - Use case diagram
 Definition:
o diagram which provides an
overview of system functionality
o Shows which use cases the
individual actor uses
 Purpose:
o To analyse the functionality the
system must include
o To give an overview of the
functionality and how it is linked
o To analyse how the actors
should use the system
 Challenges:
Construction
elements:
Package name
Package
No. and use
case name
Use case
«extends»
Communication
arrow
<<include>>
o To simplify the complex
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UML use cases – Actors
 Actor:
Construction
elements:
o Person (or system), which
uses the system (think in
terms of roles)
 Purpose:
Aktør
o To analyse which actors will
use the system
o To analyse how the use of
the actors is linked
Actor
 Challenges:
o It is NOT an organisational
chart (no organisational
linkages required)
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Specialisation /
Generalisation
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Example of use case diagram
Web store
Actor
(person)
Free search
Find an
item
Customer
Structured
search
<<include>>
Order an
item
<<extend>>
Order fast
delivery
Actor
(system)
SADAD
Check
order
Registered
customer
use case
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Use case definition + description - the process
Initial state:
- A stakeholder analysis has been performed
- Processes have been modeled
Final state:
- All use cases identified and documented
Draw
use case
packages
Audit business
process
and term model
Agency
Draw
use case
diagrams
Link to:
-Business Process
-Term modeling
Identify
actors
Complete
verbal
descriptions
Identify variants,
exceptions,
and start &
end conditions
no
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All
Use Cases
Finished ?
yes
Prerequisites
 Always begin by making a stakeholder analysis! (In case it
has not been done during process modelling)
o A good way of discovering new use cases
o A high degree of confidence that all relevant use cases are included
o The use case actors are often only part of the overall pool of
stakeholders
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Draw use case packages
1. Draw use case packages - for each business process
o
o
o
Base it on the processes
Has a thorough stakeholder analysis been done?
Put all actors for each business process on the packages
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Grouping of business functionality – Use case packages
 Use case packages divide use cases into packages that make
business sense
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Typically, cases that belong to a given process
…But it could also be use cases in a given topic / with particular
actors / other
 The packages help to provide overview
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If a documentation tool is used,
use cases may be organised as illustrated
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Draw use case diagrams
2. Draw use case diagrams - for each package
o
o
Which of the process diagram activities are relevant to the
solution?
An activity in a process corresponds to a use case (using this
method)
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Use Case Example
Use case diagram:
”Work Permit”
Work Permit
Request Work Permit
Employee
View decision
MoL new solution
Process request
SADAD
Company HR officer
Payment
MoI system
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Identify actors
3. Identify actors - for each use case
o
o
o
o
Who or what initiates the use case?
Split the actors into roles (not e.g. according to organisational dependence)
Any specialisations of an actor?
Split the actors into those that initiates (triggers) a use case, and those that
are passive actors (e.g. received data)
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Complete verbal description
4. Complete verbal description - for each use case
o
o
o
o
What is the purpose of the use case?
What needs to be done for the use case to begin? (start conditions)
Describe the steps in the use case
o What does the actor do? How does the system react?
What is the result of the use case? (end conditions)
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Use cases – Verbal description
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Use Case - verbal description
There is no standardised notation for how a
use case is described, verbally
The description typically includes:
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The Use Case name
Purpose
Actors
Start conditions (premises)
Description of the use case steps
Any exceptions
Any variants
End conditions (result)
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Use cases – Verbal description
 Use case descriptions always include a highway
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And may contain both variants and exceptions
 The highway describes:
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The way the use case is typically run through
 Variants describe:
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Alternative ways the use case may be run through
The highway and variants can be equally important
Start and end conditions will be common with the highways
 Exceptions describe:
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Events that cause failure to perform use case as described
I.e. end conditions are not met
- Start and end conditions are often under estimated!
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Make sure they are precise and well-defined
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Identify variants and exceptions
5. Identify all variants and exceptions and firm up the start and
end conditions
o What alternative routes would complete the use case?
o Any exceptions that would make the use case stop?
o Review the start and end conditions once again
- Are they precise and well-defined?
- Have all variants been considered?
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Audit business process and term model
 After completion of use cases (or during) a need will often
rise to adjust the process diagrams
o You gain knowledge as you dig deeper into the material
o The activities (and their order) may need adjustment
o You typically discover new actors/roles and new interfaces with other
systems / stakeholders
 Need to add new terms to the term model
o And maybe correct the use case descriptions to ensure strict use of
the terms in the term model
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Use cases – best practice
 The grain of use cases – what is the right size for a use
case?
o A UC must contain a complete task that needs solving – not just a
step in a task
o Well-defined start and end conditions
o Feel your way forward – it takes experience!
 The aggregate use cases do not need to reflect a workflow!
o If you do that, the use cases may well be too fine-grained
 Naming a UC – use imperative verbs!
o E.g. ”Acquire car” – ”Search for car” – ”Get FDM test” – etc.
o A good idea to attach numbers to the use cases (not meaningful
IDs!)
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Definition of use cases - tips
 Know your business!
o Be business oriented
o The professional experts must participate in the completion of use cases
 Keep matters abstract
o Describe functionality – not solution designs
o Keep use case descriptions free from ”computer monitor-thinking”
 Requirement specification with creativity and visions
o It is important that project participants are visionary and do not ”re-create”
existing solutions
 You may want a resource able to coordinate business and technical
aspects
o Has an idea of how a use case can be technically realised
o Can discuss issues with the technical staff
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