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Systems Use Case Descriptions
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Contents Review Systems Use Case Descriptions Systems Use Case Authoring
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The Process so far Draw Business Use Case Diagram to
capture the Business Processes (WP1) Write Business Use Case Descriptions
(WP1) Fact Finding
Interviewing the Client for Technical, Functional, Data Requirements
Identify the functions of the new system Draw Systems Use Case Diagrams (WP2)
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Contents Review Systems Use Case Descriptions Systems Use Case Authoring
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Systems Use Case Descriptions Accompany the systems use case
diagram Lay out the sequence of
interaction between the user and the system
Diagrams provide high-level view and textual description provides detail
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Systems Use Case Descriptions Based on the dialog metaphor
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Designing Dialogs The process of designing the
overall sequences that users follow to interact with an information system
the sequence in which information is displayed to and obtained from the user
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Systems Use Case Descriptions The (systems) use case descriptions
provide the substance of the (systems) use case model and they are the basis for most of the …modeling work…More than 90% of the (systems) use-case model lies beneath the surface, in the textual use-case descriptions themselves. *
*Use Case Modeling, Kurt Bittner & Ian Spence
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Systems Use Case Descriptions “The use case description tells a story of
how a system and its actors collaborate to achieve a specific goal
This collaboration takes the form of a dialog between the system and its actors
It is a step-by-step description of a particular way of using a system”*
*Use Case Modeling, Kurt Bittner & Ian Spence
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Systems Use Case Descriptions “Just like a story, every use case should
have a clear beginning (how the actor
starts the use case) Middle (how the system and actors
work together) End how the use case is concluded”*
*Use Case Modeling, Kurt Bittner & Ian Spence
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Systems Use Case Descriptions Not a complete description of all
possible ways that some task is performed
Does not say how the system is designed or implemented
Describes typical ways (or cases) of using the system*
*Use Case Modeling, Kurt Bittner & Ian Spence
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Systems Use Case Descriptions Systems use Case descriptions are
required to define, in detail, the processing that needs to happen in each use case
The use case diagram provides a quick view of the goal of the use case by examining the case name and associations
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Systems Use Case Descriptions The systems use case description
must include: Who the actors are and how many of
them are interacting with the system at any point in time
What data is used and how All normal logic All exception and error logic
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Preconditions & Postconditions Preconditions
State of the system at the start of use case
Postconditions State of the system at the end of use
case Can be included in the systems use
case description
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Preconditions & PostConditions Precondition
The user must have been authenticated The user must be authorized The system load is 10% below maximum
Postcondition The user’s account has been updated All transactions have been rolled back or
committed
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Contents Review Systems Use Case Descriptions Systems Use Case Authoring
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Systems Use Case Authoring Systems use case descriptions do
not pop into existence spontaneously
They begin by identifying the use case and create a brief description
This description is fleshed out until the final use case description is ready
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The Authoring Life Cycle
Discovered Briefly Described
BulletedOutline
EssentialOutline
DetailedDescription
Systems Use CaseSpecification
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Life Cycle: Discovery Through the Table identifying
Functions Through experience Shown on a Systems Use Case
diagram Place holder for the Systems Use Case
description A visual index, providing a context for the
descriptions
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Life Cycle: Briefly Described Once the Systems Use Case has been
identified, it should be described Example: Rent a Video Systems Use
Cases This Systems Use Cases describes how
a Video Rental Clerk uses the system to identify a customer, process a video, process the payment, produce a rental transaction and produce a receipt.
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Life Cycle: Essential Outline Focuses on only the most important behaviour
of the system Presents a “black box” view of the system in
order to focus on getting right what the system must do
Emphasizes usability Helps describe user intent and actions, along
with the observable response of the system Does not describe what is happening inside
the system
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Example: Essential Outline
Action by Actor System Response
Request Customer Information
Display Customer Information
Provide information on all videos to be rented
Record Video information
Provide payment details Record payment details
Complete Transaction Record transaction and provide receipt
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Essential Outline The use case in point form Very useful for generating user
interfaces Too much detail can limit the
freedom of the user interface designers
Adding details might inadvertently suggest what the interface should look like
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Life Cycle: Detailed Description The detailed description fills in the
details of the essential outline Begins by expanding the details of
the system response Is changed to a narrative form that
reads more like a story or a series of detailed steps
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Example: Conversational Form
Action by Actor
System Response
Request Customer Information
Obtain customer name and enter it into system to display information on the customer.
Provide information on all videos to be rented
Get the list of videos to be rented and enter it into the displayed customer information form. Compute amount owing for rental and tell customer.
Provide payment details
Get credit card, enter into system, and obtain verification.
Complete Transaction
Finalize transaction, committing it to permanent storage and print receipt for customer.
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Example: Narrative Form1. The customer selects videos and presents
them to the clerk. The clerk gets the customer’s name and accesses their customer information on the system.
2. The videos to be rented are entered into the customers information and the amount owing is calculated. The customer is told the amount owing.
3. …..
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Life Cycle: Fully Described Fully described use cases are:
Testable Understandable Unambiguous Correct Complete attainable
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User Interface Mockups A picture of what a user interface
will look like Drawn with a tool like PowerPoint Gets feedback on the interface
without building it Ensures that the requirements are
correctly understood
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Drawing Mockups Copy the following graphics to
make screen layouts.Button Single-line Edit Box
Radio Button (selected)
Radio Button (not selected)
Multi-line Edit Box-This changes its size according to the typing
Check Box (selected)
Check Box (not selected)
Combo Box
List BoxOr Combo Box DropdownUse it either way.
Window or Dialog Box
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Example: Mockup
OK
Type your comment here.
Halt and Catch Fire
Recover Brilliantly
Add manual comment to system log:
System Recovery Options
Recovery Method
Cancel
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Dialog Charts Layout the sequence of screens
displayed to the user Show how user can navigate from
one screen to another Each screen symbol contains:
Screen name Reference number Numbers of screens user can return to
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Dialog Charts
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Example: Dialog Chart