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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