Requirements
Functional requirements  Use-cases
Actors and use cases
Use-case diagram
Brief notation
Prioritization
Fully dressed notation
What is a use case?
A use-case describes a working procedure for a
specific actor/user of an IT system.
A use-case is used to show the interaction
between actor and IT system
Functional requirements as use-cases outline, in
what way the IT system are going to support the
user
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Good or Bad Use-cases?
• Criteria:
– Completed; goal fulfilled; coffee break
– Small create, read, update and delete tasks are gathered in
one description (CRUD)
Good or bad?
Administration of books
Register the title of a
book
Loan of book
Update reservation
Delete reservation
Check: Are all tasks included?
– Are all actor tasks
described?
– Are critical tasks
included?
– Can all data be created,
read, updated and
deleted (CRUD)?
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What is an actor?
An actor is something with behaviour that
interacts with the IT system:
Person identified as a user role, e.g. cashier, salesman,
stock employee
Another computer system
A device e.g. a temperature sensor
Primary actor: Has user goals fulfilled through
use-case
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Use case diagram
Use cases from the event table is displayed in a
UML use case diagram
Use case diagram is a graphic model of the
system's functionality and communication with
the stakeholders
includes:
Use cases
Actors
Associations between use cases and the actor(s) who
interact with the use case
delimitation
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Use case diagram for customer - order
Small use cases can be
assembled in
CreateReadUpdateDelete
(CRUD) use-cases
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Description formats for use cases
Overall textual descriptions in a short summarized form
(customer-facing)
Brief: textual description of a happy days scenario
Casual: variations of happy days scenario
Detailed descriptions of the "expanded" form - fully
dressed
The steps in the use case and variations thereof are described in
detail
A graphical representation of the interaction of the use
case in a system sequence diagram - SSD (in a later
session)
All use cases described in brief and / or causal. Only the
critical described fully dressed with associated solid state
and contracts
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Use case description, Brief
Template for brief description:
Use case: Name of the use case
Description: An overall but complete description of who
initiates the use case, the expected system actions and
responses of this that adds value to an actor
Input to the system actions retrieved from the
event table: Steps in use case
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Use-case description Casual
In addition to the brief form there can be added
alternative scenarios in the Causal format
Examples of alternative scenarios for the use-case:
Register Order:
If the goods are sold the system indicates when new
products are expected home, so the customer can be
informed
If the customer wishes to pay immediately ......
.......
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Prioritazation af use-cases
According UP designing, implementation and testing is
done in small chunks through a number of iterations
(steps)
The highest priority and most complex use-case is
analysed, designed and coded in the first iterations (so
one must assume that the rest also can be made)
The steps in development of use-cases are:
1.
2.
3.
Use cases identified and they appear in a UML use-case diagram
Then, they are described in brief or casual form.
On this basis, use cases are prioritized (based on architecturerelated importance, risks and business value), and then the most
important are analysed for the design of prototypes and "fully
dressed" descriptions.
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Use-case description: ”Fully dressed”
Detail storyline in use-case in a number of steps
(flow of events) consisting of:
Actor action<-> System response
Add actor, pre- and post-conditions
Use essential and black box style
Brief- and/or casual descriptions and mock ups
are used as the basis for the fully dressed
descriptions.
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Example: Use case: Register Order
Flow of events in fully dressed description
1.
2.
Use-case starts with a customer inquiry over the telephone to order goods
Shop assistant begins a new order
the system creates a new order
3.
Shop assistant Specifies the ID of the desired products
4.
The system returns the item description, price, sub total and running total
5.
Shop assistant adds the desired number of items
1. The system adds the items
6.
Steps 4-7 are repeated until all items are added
7.
Shop assistant specify delivery information
8.
The system validates the data and record customer
9.
Shop assistant completes order
10. The System saves the order
11. Shop assistant request for an order form and invoice
12. The system prints a confirmation
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