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7/25/2014

Use Cases
Chapter 3
Systems Analysis and Design in a Changing World 6th Ed Satzinger, Jackson & Burd

Chapter 3 Outline
Use Cases and User Goals Use Cases and Event Decomposition Use Cases and CRUD Use Cases in the RMO Business Case User Case Diagrams

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Learning Objectives
Explain why identifying use cases is the key to defining functional requirements Describe the two techniques for identifying use cases i.e. user goal technique and event decomposition technique to identify use cases Apply the CRUD technique to validate and refine the list of use cases Describe the notation and purpose for the use case diagram Draw use case diagrams by actor and by subsystem

Overview
Chapter 2 provided an overview of systems analysis activities, functional and non-functional requirements, modelling, and information gathering techniques This Chapter focuses on identifying and modelling the key aspect of functional requirements – Use Cases In the RMO Tradeshow System from Chapter 1, some use cases are Look up supplier, Enter/update product information, Enter/Update contact information This chapter’s opening case Waiters on Call, examples of use cases are Record an order, Record delivery, Update an order, Sign in driver, Reconcile driver receipts, Produce end of day deposit slip, and Produce weekly sales reports
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Use Cases
Use Case — An activity that the system performs, usually in response to a request by a user Use cases define functional requirements Analysts decompose the system into a set of use cases (functional decomposition) Two techniques for Identifying use cases 1. User Goal Technique 2. Event Decomposition Technique Name each use case using Verb
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1. User Goal Technique
This technique is the most common in industry Simple and effective Identify all of the potential categories of users of the system Interview and ask them to describe the tasks the computer can help them with Investigate further to refine the tasks into specific user goals, “Need to Ship items, Track a shipment, Create a return”
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Example: User Goal Technique
Some RMO CSMS Users and Goals

Steps: User Goal Technique
1. 2. 3. 4. 5. 6. 7. 8.

Identify all the potential users for the new system Classify the potential users in terms of their functional role (e.g., shipping, marketing, sales) Further classify potential users by organizational level (e.g., operational, management, executive) For each type of user, interview them to find a list of specific goals they will have when using the new system Create list of preliminary use cases organized by type of user Look for duplicates with similar use case names and resolve inconsistencies Identify where different types of users need the same use cases Review the completed list with each type of user and then with interested stakeholders
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2. Event Decomposition Technique
More Comprehensive and Complete Technique
Identify the events that occur to which the system must respond. For each event, name a use case (verb) that describes what the system does when the event occurs

Template: Events in “Charge Account
Processing System” that Lead to Use Cases

Event – Something that occurs at a specific time and place, can be described, and should be remembered by the system
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Types of Events
External Event
An event that occurs outside the system, usually initiated by an external agent or actor

External Event Checklist
External agent or actor wants something resulting in a transaction
Customer buys a product

Temporal Event
An event that occurs as a result of reaching a point in time

External agent or actor wants some information
Customer wants to know product details

State Event
An event that occurs when something happens inside the system that triggers some process Reorder point is reached for inventory item
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External data changed and needs to be updated
Customer has new address and phone

Management wants some information
Sales manager wants update on production plans
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Template: Finding the actual event that

Temporal Event Checklist
Internal outputs needed at points in time
Management reports (summary or exception) Operational reports (detailed transactions) Internal statements and documents (including payroll)

affects the system…

External outputs needed at points of time
Statements, status reports, bills, reminders

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Template: Tracing a sequence of transactions resulting in many events…

Steps: Event Decomposition Technique
1. 2. 3. 4. 5.

6. 7.

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Consider the external events in the system environment that require a response from the system For each external event, identify and name the use case that the system requires Consider the temporal events that require a response from the system For each temporal event, identify and name the use case that system requires and then establish point of time that will trigger use case Consider the state events that the system might respond to, particularly if it is a real-time system in which devices or internal state changes trigger use cases. For each state event, identify and name the use case that the system requires and then define the state change. When events and use cases are defined, check to see if they are required by using the perfect technology assumption. Do not include events that involve such system controls as login, logout, change password, backup, restore the database, as these are put in later.
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Benefits: Event Decomposition Technique
Events are broader than user goal — Capture temporal and state events Help decompose at the right level of analysis — An Elementary Business Process (EBP) EBP is a fundamental business process performed by one person, in one place, in response to a business event Uses perfect technology assumption to make sure functions that support the users work are identified and not additional functions for security and system controls
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Use Cases and CRUD Technique
CRUD is Create, Read/Report, Update, and Delete Often introduced in database context Technique to validate, refine or cross check use cases NOT for primarily identifying use cases For Customer domain class, verify that there are use cases that create, read / report, update, and delete (archive) domain class

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Steps: CRUD Technique
1.

CRUD Technique
Use Case vs. Domain Class Table To summarize CRUD analysis results, create a matrix of use cases and domain classes indicating which use case C, R, U, or D a domain class

Identify all the data entities or domain classes involved in the new system; (Chapter 4) For each type of data (data entity or domain class), verify that a use case has been identified that creates a new instance, updates existing instances, reads or reports values of instances, and deletes (archives) an instance. If a needed use case has been overlooked, add a new use case and then identify the stakeholders. With integrated applications, make sure it is clear which application is responsible for adding and maintaining the data and which system merely uses the data
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3.

4.

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Use Cases and Brief Use Case Descriptions
Brief use case description is often a one sentence description showing the main steps in a use case

Example: RMO CSMS Project Use Cases
Sales & Order Fulfillment Subsystem

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Example: RMO CSMS Project Use Cases
Customer Account, Marketing & Reporting Subsystem

Use Case Diagrams & Symbols
Use Case Diagram — A UML model used to graphically show uses cases and their relationships to actors

Recall UML is Unified Modelling Language, the standard for diagrams and terminology for developing information systems Actor is the UML name for a end user Automation Boundary — The boundary between the computerized portion of the application and the users who operate the application

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Example: RMO CSMS Project Use Case Diagram
Customer Account Subsystem (Actors: ALL)

Example: RMO CSMS Project Use Case Diagram
Sales Subsystem (Actor: CUSTOMER)

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Example: RMO CSMS Project Use Case Diagram
Sales Subsystem (Actor: CUSTOMER SERVICE REP. & STORE SALES REP.)

Example: RMO CSMS Project Use Case Diagram
Sales Subsystem: The Relationship

A relationship between use cases where one use case is included within the other use case — like a called subroutine. Arrow points to subroutine

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Steps: Use Case Diagrams
1.

Summary
This chapter is the first of three that focuses on modelling functional requirements as a part of systems analysis Use cases are the functions identified, the activities the system carries out usually in response to a user request Two techniques for identifying use cases are the user goal technique and the event decomposition technique The user goal technique begins by identifying end users called actors and asking what specific goals they have when interacting with the system The event decomposition technique begins by identifying events that occur that require the system to respond. Three types of events include external, temporal, and state events Brief use case descriptions are written for use cases The CRUD technique is used to validate and refine the use cases identified The use case diagram is the UML diagram used to show the use cases and the actors The use case diagram shows the actors, the automation boundary, the uses cases that involve each actor, and the relationship. A variety of use case diagrams are draw depending on the presentation needs of the analysis
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Identify all the stakeholders and users who would benefit by seeing a use case diagram Determine what each stakeholder or user needs to review in a use case diagram: each subsystem, for each type of user, for use cases that are of interest For each potential communication need, select the use cases and actors to show and draw the use case diagram. There are many software packages that can be used to draw use case diagrams Carefully name each use case diagram and then note how and when the diagram should be used to review use cases with stakeholders and users
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