Use Cases - heracleia.uta.edu

1 Use CasesUse Cases in Iterative Development CSE 5324, Summer 2017 Outline What and Why? Major Elements of a Use case Guidelines for Writing Use Cases Use case Diagrams Use case -Driven DevelopmentCSE 5324, Summer 2017, Ali Sharifara UTA2 Use- case What it is: Text storyWidely used to discover and record (mostly functional) requirements What is it about: Some actor(s)using a system to meet specific goals Answering questions: Who is using the system, whatare their typical scenarios of use, and what are their goals? What it is NOT: Not object-oriented Not a diagram UML use Cases diagrams are secondary-value artifacts Focus: use Cases , not use case diagrams CSE 5324, Summer 2017, Ali Sharifara3 Example: Point of Sale 1. Customer arrivesat a checkout (+goods)2. Cashier usesPOS system to record items 3. System presentsa running total and line-item details. 4. Customer enterspayment information, which the system validates and System updatesinventory.

2 6. Customer receivesreceipt from the system and 5324, Summer 2017, Ali Sharifara4 Actors, Scenarios, and Use Cases Actor: Entity that shows a behavior, : a person (role), computer system, or organization Scenario: specific sequenceof actionsand interactions between actors and a system use case instance Use case : collection of related success& failurescenarios that describe an actor using a system to support a goal CSE 5324, Summer 2017, Ali Sharifara5 Use case Example with Scenarios (casual format) UC Handle Returns Main success Scenario: A customer arrives at a checkout with items to return. The cashier uses the POS system to record each returned item .. Alternate Scenarios: If the customer paid by credit .. If the item identifier is not found in the system .. If the system detects failure to communicate with the external accounting system ..CSE 5324, Summer 2017, Ali Sharifara6 Use- case Model Set of all writtenuse Cases Model of the system s functionality and environment Unified Process (UP) defined artifact within the requirements discipline May optionally include a UML use case diagram Use Cases , actors, and their relationships context diagram CSE 5324, Summer 2017, Ali Sharifara7 System Context diagram - Example A systemcontext diagram(SCD) is a diagramthat defines the boundary between the system, or part of a system, and its environment, showing the entities that interact with it.

3 Thisdiagram is a high level view of a 5324, Summer 2017, Ali Sharifara8 Three Kinds of Actors Primary actor Has user goals fulfilled through using services of the system under discussion drives the use Cases Supporting actor Provides a service to the system under discussion , payment authorization service implies: clarification of external interfaces and protocols needed Offstage actor Has an interest in the behavior of the use case , but is not primary or supporting , a government tax agency CSE 5324, Summer 2017, Ali Sharifara9 Use case Format Brief Succinct one-paragraph summary Usually the main success scenario Done during early requirements analysis Should take only a couple of minutes Casual Informal paragraph format Multiple paragraphs covering various scenarios Fully Addressed Details all steps and variations Includes supporting sections such as preconditions and success guarantees mainly done after many use Cases are identified and during early requirements workshop for high-value and high-risk requirements ( , core architectural)

4 CSE 5324, Summer 2017, Ali Sharifara10A Template for Fully Dressed Style CSE 5324, Summer 2017, Ali Sharifara11 Coffee Maker Example Example of a semi fully dressed use case Coffee Maker Example ~sharifara/5324 5324, Summer 2017, Ali Sharifara12 Write in an Essential Style (early phase) Keep the user interface out Focus on actor intent User s intentionsand system s responsibilitiesrather than their concrete actions Example Manage Users identifies self. authenticates identity. Another is concretestylethat embeds user interface decisions Avoid during early analysis Example1. Administrator enters ID and Password in a dialog box CSE 5324, Summer 2017, Ali Sharifara13 Write Black-Box Use Cases Focus on what the system must do, ., the behavior or functional requirements Noton howit will do (the design) Examples: Good: System records the sale Bad: The system writes the sale to the database.

5 Worse: System generates SQL INSERT statement for the sale CSE 5324, Summer 2017, Ali Sharifara14 Guideline: Write Terse Use Cases System authenticates .. , rather than The System authenticates .. CSE 5324, Summer 2017, Ali Sharifara15 Take an Actor and Actor-Goal Perspective Use case definition A set of use- case instances, where each instance is a sequence of actions a system performs that yields an observable result of value to a particular actor Write requirements focusing on the users/actors of a system Asking about their goals and typical situations and what they consider a valuable result CSE 5324, Summer 2017, Ali Sharifara16 Actor-Goal List CSE 5324, Summer 2017, Ali Sharifara17 One Column vs Two Column Format Two column emphasizes interaction CSE 5324, Summer 2017, Ali Sharifara18 How to Find Use Cases ? Choose the system boundary What you are building? Wo will be using the system? What else will be used that you are not building?

6 Find primary actorsand their goals Brainstorm the primary actors first Who starts and stops the system? Who gets notified when there are errors or failures? Define use Cases that satisfy user goals Prepare an actor-goal list (and not actor-task list) In general, one use case for each user goal Name the use case similar to the user goal CSE 5324, Summer 2017, Ali Sharifara19 What Tests Can Help Find Useful Use Cases ? Which of these are valid use Cases ? Negotiate a Supplier Contract Handle Returns Log in Move Piece on the Game Board CSE 5324, Summer 2017, Ali Sharifara20 What Tests Can Help Find Useful Use Cases ? Which of these are valid use Cases ? Negotiate a Supplier Contract Handle Returns Log in Move Piece on the Game Board All of these can be use Cases At different levels, Depending on the system, boundary, actors, and goals CSE 5324, Summer 2017, Ali Sharifara21 What Tests Can Help Find Useful Use Cases ?

7 Rather than asking What is a valid use case ? More practical question: What is a useful level of focusto express use Cases for application requirements analysis? Rules of thumb The Boss Test The EBP Test The size testCSE 5324, Summer 2017, Ali Sharifara22 The Boss test What have you been doing all day? Your reply logging in! Is your boss happy? No value? No good use case ! CSE 5324, Summer 2017, Ali Sharifara23 The Size Test A use case is very seldoma single action or step Instead, a use case typically has many steps, and in the full dressed format will often require 3-10 pages of 5324, Summer 2017, Ali Sharifara24 The EBP Test An Elementary Business Process is a term from the business engineering field A task performed by one person in one place at one time, in response to a business event, which adds measurable value and leaves the data in a consistent state. Focus on use Cases that reflect EBPs.

8 Not a single small step, , delete a line item or print a document Not a big task taking days, , negotiate a supplier contract CSE 5324, Summer 2017, Ali Sharifara25 Applying Tests Negotiate a supplier contract Much broader than EBP, rather a business use case Handle returns OK with the Boss. EBP. Size is good. Log in Boss is not happy is this is all you do all day! Move piece on game board Single step fails the size test. CSE 5324, Summer 2017, Ali Sharifara26 Use case diagrams Use case diagrams describe whata system does from the standpoint of an external observer. The emphasis is on what a system does rather than how. Use case diagrams are closely connected to scenarios. A scenariois an example of what happens when someone interacts with the system. A scenario is a specific sequence of actions and interactions between actors and the 5324, Summer 2017, Ali Sharifara27A scenario Here is a scenario for a medical clinic.

9 A patient calls the clinic to make an appointment for a yearly checkup. The receptionist finds the nearest empty time slot in the appointment book and schedules the appointment for that time slot. " We want to write a use case for this scenario Remember: a use case is a summary of scenarios for a single task or goal. CSE 5324, Summer 2017, Ali Sharifara28 Use Cases Step 1:Identify the actors As we read the scenario, define those peopleor systemsthat are going to interact with the scenario. A patientcalls the clinic to make an appointment for a yearly checkup. The receptionistfinds the nearest empty time slot in the appointment book and schedules the appointment for that time slot. " CSE 5324, Summer 2017, Ali Sharifara29 Questions for Identifying People Actors Who is interested in the scenario/system? Wherein the organization is the scenario /system be used? Who will benefit from the use of the scenario/system?

10 Who will supplythe scenario/system with this information, use this information, and remove this information? Does one person play severaldifferent roles? Do several people play the same role?CSE 5324, Summer 2017, Ali Sharifara30 Use Cases So as we read our scenario, what or who is the actor? A patient calls the clinic to make an appointment for a yearly checkup. The receptionist finds the nearest empty time slot in the appointment book and schedules the appointment for that time slot. " The actor is a Patient. CSE 5324, Summer 2017, Ali Sharifara31 Use Cases The picture below is a Make Appointment use case for the medical clinic. The actor is a Patient. The connection between actor and use case is a communicationassociation (or communication for short). Actors are stick figures. Use Cases are ovals. Communications are lines that link actors to use 5324, Summer 2017, Ali Sharifara32 Use case Components The use case has three components.