The document discusses use cases and scenarios in software engineering. It defines use cases as narratives that describe how users will interact with a system. Use case diagrams visualize relationships between actors and use cases. The document provides examples of use case diagrams and describes how to document use cases, including typical elements like actors, flows, and alternate flows. It provides guidance on writing effective use cases, such as defining goals and needs for each actor.

1. Software Engineering
Prof.Dr.ir. F. Gielen
Functional Requirements
Use cases & System Scenarios
Vakgroep Informatietechnologie – IBCN

2. Use Cases & Scenarios
 Use cases, sometimes called user scenarios,
are narratives or flow diagrams that describe
how users will interact with a system.
 Some people also refer to them as task
analysis or user flows. Regardless of what
you call them, the idea is the same:
 Illustrate to people scenarios or specific tasks
which users will perform on the system.
 Illustrate how the system interacts with other
systems.
Vakgroep Informatietechnologie – Onderzoeksgroep IBCN p. 2

3. Use Case Diagram
 Use case diagrams are created to visualize
the relationships between actors and use
cases
 Use cases are a visualization of the functional
requirements of a system
Vakgroep Informatietechnologie – Onderzoeksgroep IBCN p. 3

4. Example : Use Case Diagram
Vakgroep Informatietechnologie – Onderzoeksgroep IBCN p. 4

5. Actors & user profiles (persona’s)
 An actor is someone or something that must
interact with the system under development
 Before starting any project it is imperative to
understand the target audiences. User profiles
(also referred to as user personas) are an excellent
way to document and illustrate realistic sample
users.
Vakgroep Informatietechnologie – Onderzoeksgroep IBCN p. 5

6. Use Cases
A use case is a pattern of behavior the
system exhibits
 Each use case is a sequence of related
transactions performed by an actor and the
system in a dialogue
 Actors are examined to determine their
needs
 Passenger – Search for Flights, Make
Reservation, Pay for Flight
Vakgroep Informatietechnologie – Onderzoeksgroep IBCN p. 6

7. Documenting Use Cases
A use case specification document is
created for each use case
 Written from an actor point of view
 Details what the system must provide to
the actor when the use case is executed
 Typical contents
 How the use case starts and ends
 Normal flow of events
 Alternate flow of events
 Exceptional flow of events
Vakgroep Informatietechnologie – Onderzoeksgroep IBCN p. 7

8. Template for Use Cases
 Textual description in prose
 Priority|Complexity (High, Medium or Low)
 Related informal requirements
 Actors
 Events (triggering, during execution, ...)
 Preconditions
 Main success scenario (MSS - Diagram)
 Extensions on the MSS
 Postconditions after success and failure
 Related use cases
Vakgroep Informatietechnologie – Onderzoeksgroep IBCN p. 8

9. System Sequence diagram
Black Box Sequence Diagram
Vakgroep Informatietechnologie – Onderzoeksgroep IBCN p. 9

10. Write an effective Use Case : eBay
STEP 1. Define your use case actors
-> An actor can be a person or a system
Vakgroep Informatietechnologie – Onderzoeksgroep IBCN p. 10

11. Write an effective Use Case: eBay
STEP 2. Define your use case Actor Goals & Needs
-> What are the goals & needs of each actor
-> Create initial list of high level use cases
-> Effective use cases should have understandable actors and goals
Vakgroep Informatietechnologie – Onderzoeksgroep IBCN p. 11

12. Write an effective Use Case: eBay
STEP 3. Identify reuse opportunity for use cases
-> Identify the duplicated behavior
-> Create a generic actor or a generic use case
-> This will make the system more understandable and flexible
Vakgroep Informatietechnologie – Onderzoeksgroep IBCN p. 12

13. Write an effective Use Case: eBay
STEP 4. Create a use case index
-> Every use case has attributes to himself and to the project
-> Project level:
- Technical complexity: High Medium or Low
- Business priority
-> Make a selection of scenarios for elaboration (in scope) based on
the combined weight of complexity & priority.
-> It will serve as a master inventory to help write effective use cases
for the requirements phase of the project
Vakgroep Informatietechnologie – Onderzoeksgroep IBCN p. 13

14. Write an effective Use Case: eBay
STEP 5. Identify the key components of your use case
->The actual use case is a textual & graphical representation
illustrating a sequence of events. There are several components of a
use case which we will review
-> In this table, you get a basic understanding of what is in the use
case and review each element as you progress through your use
cases
Use Case Element Description
Use Case Number ID to represent your use case
Use Case Name The name of your use case, keep it short and sweet
Use Case Description Elaborate more on the name, in paragraph form.
Primary Actor Who is the main actor that this use case represents
Precondition What preconditions must be met before this use case can start
Trigger What event triggers this use case
The basic flow should be the events of the use case when everything
is perfect; there are no errors, no exceptions. This is the "happy day
Basic Flow
scenario". The exceptions will be handled in the "Alternate Flows"
section.
Alternate Flows The most significant alternatives and exceptions
Vakgroep Informatietechnologie – Onderzoeksgroep IBCN p. 14

15. Write an effective Use Case: eBay
STEP 6. Name and briefly describe your use case
->start creating your use case
->use plain English and keep it simple!
Use Case Number: 1
Use Case Name: Buyer Places a Bid
An EBAY buyer has identified an item they wish to buy,
Description: so they will place a bid for an item with the intent of
winning the auction and paying for the item.
Vakgroep Informatietechnologie – Onderzoeksgroep IBCN p. 15

16. Write an effective Use Case
STEP 7. Create the use case basic flow
->this represents the most important course of events
-> No errors or exceptions
use UML Sequence diagrams
SYSTEM LEVEL &
BLACK BOX
STEP 8. Create the use case alternate flow
->An exception or error flow to any line item in your basic flow
-> An additional flow, a flow that COULD happen
(example: While a costumer places an order, their credit card failed)
Vakgroep Informatietechnologie – Onderzoeksgroep IBCN p. 16

17. Write an effective Use Case
STEP 9. Consolidate and create the use case diagram
Vakgroep Informatietechnologie – Onderzoeksgroep IBCN p. 17

18. Scenario document – use case part
 Use case diagram: UML
 Use case index: TEXT
 Use case description for the top 3
scenario’s: TEXT + UML
 sunny day
 rainy day
Vakgroep Informatietechnologie – Onderzoeksgroep IBCN p. 18

19. Visio: Use Cases – Modeling tool
For modeling the Use Cases, we use the program
“Visio”
Athena: -> Office -> Extra -> Visio 2010
 If you want the right “Shapes”:
Download the stencil from www.softwarestencils.com/uml
Open stencil in Visio
Use the right shapes
Vakgroep Informatietechnologie – Onderzoeksgroep IBCN p. 19

20. Agile Resources
 UML & Agile:
 www.agilemodeling.com/essays/umlDiagrams.htm
 Use Cases
 www.agilemodeling.com/artifacts/useCaseDiagram.htm
 Use case template: Minerva
 Sequence Diagrams:
 www.agilemodeling.com/artifacts/sequenceDiagram.htm
Vakgroep Informatietechnologie – Onderzoeksgroep IBCN p. 20