Use Case Modeling CEN 5016: Software Engineering © Dr. David A. Workman School of EE and Computer Science University of Central Florida February 1, 2005 (Revised February 14, 2006)

September 28, 2005(c) Dr. David A. Workman2 Requirements Capture Input Client approaches Developer with a problem and or product concept. This may be expressed verbally or in the form of a document (Statement of Work (SOW)) (Request for Proposal (RFP)) Activities Developer interacts with Client and Users to elicit product requirements. This involves face-to-face meetings and possibly the exchange of technical documents. The Developer must determine as completely and precisely as possible the following information: –cost and time constraints –target system platform and operational environment –user groups –functional capabilities –non-functional constraints: quality and performance –Client and User's needs (as opposed to "wants") Outputs A complete understanding of the problem the Client and Users need to have solved. Client should be in agreement with the Developer’s assessment of the problem. This shared view of the system is captured in the form of a UML Use Case Model.

September 28, 2005(c) Dr. David A. Workman3 Use Case Model Definitions 1 A Use Case is a sequence of actions that the system performs to offer some results of value to a User. –Use cases drive the whole development process. “They offer a systematic and intuitive means of capturing functional requirements from the user’s perspective.” –A system has many types of users. Each type of user is define by an actor. Actors may be people or external systems. Actors interact with the product via one or more Use Cases. An actor role is defined by a particular set of use cases performed by that actor to accomplish a particular goal or objective. –“All actors and uses cases make up a Use Case Model.” –A good collection of use cases is central to understanding what your users want. Use Cases also present a good vehicle for project planning, because they control iterative development, … it gives regular feedback to users about where the software is going. –Use cases provide the basis of communication between the client and the developers in planning the project. 1 The Unified Software Development Process, by Rumbaugh, Jacobson, and Booch, Addison-Wesley, 1999,

September 28, 2005(c) Dr. David A. Workman4 Use Case Model Definition 2 (Fowler) A Use Case captures a typical interaction between a user and a computer system. –A use case captures some user-visible function. –A use case may be small or large. –A use case achieves a discrete objective for the user. In its simplest usage, you capture a use case by talking to typical users and discussing the various things they might want to do with the system. Take each discrete task or action they want to do, give it a name, and write up a short description. During the Elaboration phase, this is all you need to do to get started. 2 UML Distilled, by Scott & Fowler

September 28, 2005(c) Dr. David A. Workman5 Use Case Modeling Process Produce Use Case Model 1.0 Classify Data as Inputs/Outputs 1.2 Analyze RQ For Noun phrases 1.1 Analyze RQ For Use Cases & Actors 1.3 Allocate Inputs/Outputs/Actors to Use Cases 1.4 List of Noun Phrases List of Input Data List of Output Data List of Use Cases List of Actors Actor/Use Case Relationships Determine Relations Among Use Cases 1.5 Use Case Relationships Review With Customer/Users 1.6 Revise Work Products 1.7 Next Inputs: Problem Statement (SOW) Requirements Document Initial Customer/User Mtngs

September 28, 2005(c) Dr. David A. Workman6 Use Case Modeling Process Produce Use Case Model 1.0 Allocate Use Case Inputs/Outputs To Actors 1.9 Produce System Use Case Diagram 1.8 Revise Use Case Inputs/Outputs 1.10 Determine Data Relationships 1.11 Use Case Diagram List of Actor Inputs to Use Case List of Use Case Outputs to Actor List of Classes Objects and Data members Produce Class/Object Diagram 1.12 Class Diagram Review With Customer/Users 1.13 Revise Work Products 1.14 Next

September 28, 2005(c) Dr. David A. Workman7 Use Case Modeling Process Produce Use Case Model 1.0 Define System Boundary Objects For Use Case 1.16 Model Use Case Interface 1.15 Define Use Case Interaction Scenario 1.17 Use Case Interface Model Use Case Interaction Flows Produce Use Case Communication Diagram 1.18 Use Case Communication Diagram Review With Customer/Users 1.20 Revise Use Case 1.21 Next List of Use Case Interaction Objects Produce Use Case Spec 1.19 Use Case Spec

September 28, 2005(c) Dr. David A. Workman8 Use Case Modeling Process Produce Use Case Model 1.0 Review With Customer/Users 1.21 Revise Use Case Model 1.22 Complete Use Case Model 1.20 Use Case Model Review by SQA 1.23 Use Case Model Final Revision of UCM 1.24 Place Under Config. Mgmt Use Case Model Release UCM 1.26 Use Case Model

September 28, 2005(c) Dr. David A. Workman9 Use Case Model Outline Title (System Name, Author Name, Assignment, Course, Pub. Date) –TOC –List of Figures (optional for small documents) 1.System Summary –Overview of System Purpose and Context –Business Case ( business need and how this system will address this need ) –System Operation Use Case Diagram Supporting Narrative (explains diagram: operational flow, actor roles ) –System Interfaces ( External Interfaces with Actors ) 2.Use Case Specifications 1.Purpose ( function from user’s perspective ) Collaboration diagram (flow of interactions between actors and interface objects ) Narrative summary of use case purpose or function 2.Precondition (system states & triggering events ) 3.Flow of Events (nominal flow of interaction events between actor and interface objects) 4.Alternative Paths (error processing flows; special case flows ) 5.Post Condition (system states & completion events ) 6.Special Requirements (non-functional : performance and quality ) 3.Requirements Traceability 4.Glossary

September 28, 2005(c) Dr. David A. Workman10 Use Case Model: Detail Title Page and Format Document type, System Title, Author, Publication Date, Course, Assignment Table of Contents (TOC) Table of Figures (optional) 1.System Summary 1.Scope and purpose of document ( Document content, Intended audience ) 2.Business case: motivation for building the system; how it meets needs of users and organization 3.Concept of Operation Use Case Diagram Narrative explaining flow of use cases and their relationships. Identifies all actors (and perhaps key internal agents) and introduces their roles with respect to the use case(s) they engage in. Should also identify all major problem data elements consumed, manipulated, or produced by the system. 4.System Interfaces (See Next Slide) For each interface: identify the actors and use cases that exercise that interface, the problem data content, flow direction, medium and/or mechanism. For each interface: supporting diagrams illustrating actor interface (optional)

September 28, 2005(c) Dr. David A. Workman11 Use Case Model: System Interfaces ActorUseCaseActor Inputs System OutputsSystem Interface Mechanism Vehicle at Toll Booth Pay Toll with Cash Money (Coins | Bills) Transaction Receipt & Access Arm Raised [& Change] Interacts with Toll Clerk and Lane Access Arm On-Line Transaction System Pay Toll with Cash Transaction Accepted Cash Transaction (Amount Paid, Change, Date) TCP/IP …………

September 28, 2005(c) Dr. David A. Workman12 Use Case Model: Detail 2.Use Case Specifications This section should include a subsection (2.xx) for each use case identified in section 1.3. Each use case should have the following format and organization. An introductory section should be included giving a diagram and narrative describing system states and their transitions. 1.Purpose: Specify the purpose of the use case – what it accomplishes from the view of the actors involved and the service the system provides these actors. Support with a collaboration diagram. 2.Preconditions: Specify the system states that must hold before the use case is defined or can begin, AND the triggering event(s) that mark the beginning of the use case. 3.Interaction Scenario: In conjunction with collaboration and state diagrams, present the primary or normal flow of interaction events that accomplish the purpose of the use case. The collaboration diagram identifies the analysis classes involved in the scenario. 4.Alternative Scenarios: In conjunction with collaboration and state diagrams, present possible alternative flows of interaction events. This subsection can be used to describe error handling scenarios and/or alternative sub-use cases. 5.Post conditions: Specify the system states that result after the use case has completed, AND the event(s) that mark the end of the use case. 6.Other Requirements: resource constraints, other qualify factors (e.g. reliability).

September 28, 2005(c) Dr. David A. Workman13 Use Case Modeling: Activity Diagram Accept Payment Of Next Motorist Produce Receipt Release Vehicle Return Change Initial ?? [over payment] [exact Amt]

September 28, 2005(c) Dr. David A. Workman14 Use Case Modeling: Communication Diagram Toll Clerk Toll Arm 1: Pay Cash 2a: Return Change 2b: Return Receipt 3: Raise Access Arm 4: Leave Gate NOTE: Communication Diagram is UML 2.0 terminology. In earlier versions of UML, these were called Collaboration Diagrams.

September 28, 2005(c) Dr. David A. Workman15 Use Case Model: Detail 3.Requirements Traceability In this section you identify the sources of requirements and enumerate all requirements statements. A source must be associated with each requirement. This is best presented in the form of a table. 1.List all sources of requirements statements. A source can be a document, an interview with some individual (customer or user or expert), or a web site, etc. Each source should be uniquely identified (by number or acronym ). Ref[1] Customer Requirements for Jiffy Stop Simulation System Ref[2] Personal interview with Dr. David Workman, CEO of CEN A Table should be constructed, such as the one shown below, where a statement of the requirement is given (“shall” statement) and a reference to the source containing or implying the requirement statement. Requirements StatmentsRequirements Source “The system shall simulate a convenience store customer engaged in the activity of purchasing gasoline from the time the customer leaves the automobile to the time the customer returns to the automobile upon completing the scenario.” Ref[1] pp12, line 4. “The pay-by-credit scenario shall support credit cards only – no debit cards.”Ref[2].

September 28, 2005(c) Dr. David A. Workman16 Use Case Model: Detail 4.Glossary The Glossary presents an organized list of problem space terms and their definitions as elicited from the client and system users. This provides the common vocabulary by which all system stake holders communicate. All common synonyms should be included, but the most common synonym should be used consistently through the rest of the document. For example, “clerk” is the most preferred term for the person that processes purchases and interacts with the customer to collect payment for gasoline purchased – this term should be used in the body of the document. However, one should list acceptable synonyms in a format as shown below. Clerk: the convenience store agent (store employee) who processes each cash transaction for gasoline; configures the gas pump to dispense the appropriate fuel amount, and to produce a sales receipt of the transaction. Synonyms: cashier. The Glossary should capture all terms that denote problem objects and system operations or use cases. It should capture all actors that externally interact with the system and the terms that pertain to actor interfaces. The Glossary should be used as a central repository of all information that is known about a particular term.

September 28, 2005(c) Dr. David A. Workman17 Use Case Diagram Actors: perform user roles Actions: identify use cases Connectors: identify actors that participate in an action. Actor3 Actor4 Select Catalog Pay by Credit Card Place Order Arrange Payment The system to be developed. association extends includes specialization/ generalization See notes Order Product * Actor1 Actor2

September 28, 2005(c) Dr. David A. Workman18 Use Case Model Actors An actor is a role that a user plays with respect to the system. An actor is a role that requires the system to perform some function or task on its behalf, and not the converse. Since a user may play more than one role at different times, it is important to focus on roles, rather than users (job titles ). Actors carry out Use Cases; conversley, a Use Case may have several actors performing it. –For large systems, it is easier to identify the actors first and then define the Use Cases each actor would perform. –Actors do not have to be human, they could be external systems that must interface with the system in question. –User groups can be characterized or profiled in terms of the actor roles they play. –Different actors may share some set of Use Cases. This may suggest a need for assigning priorities to actors and/or defining some type of security mechanism to resolve access conflicts; the system may therefore need a mechanism for identifying a particular actor with which it is interacting. –Actors generally receive value from a Use Case.

September 28, 2005(c) Dr. David A. Workman19 Use Case Diagrams Connector: Association Bank Manager Pay by Credit Card Order Product * Customer Association defines a communication link between actors and the use cases they participate in, or between two or more use cases that have to interact (or share data) to accomplish their task. Associations are not directional, suggesting that interactions are generally bi-directional. However, UML does permit an “initiates” annotation to identify the actor or use case that initiates the interaction. Association is the default relationship when others do not apply. « initiates »

September 28, 2005(c) Dr. David A. Workman20 Use Case Diagrams Connector: Includes Bank Manager Arrange Payment Browse Catalog * Customer Includes is analogous to “whole-part” relationship between objects. One use case (the “whole”) may require several subordinate processing actions or steps (the “parts”). The subordinate actions are generally use cases themselves, but need not be. The Includes relation should always be used if the subordinate action defines a necessary step to ensure success of the superior use case, or if the superior use case has sole responsibility for ensuring that the subordinate action is performed. « initiates » Buy Product Order Product « includes »

September 28, 2005(c) Dr. David A. Workman21 Use Case Diagrams Connector: Extends Financial Institutions * In-house Dealer Extends implies that one use case is a functional extension of the capabilities of another use case. If A extends B, then A does everything B does and more. Extension usually suggests extending either the potential user base, or extending the functional capability to an existing client base – offering more services – or both. « initiates » Exchange Money Play Card Games Electronically Play Black Jack « extends » In-house Gamblers * « initiates » Casino System * Remote Gamblers See Notes

September 28, 2005(c) Dr. David A. Workman22 Use Case Diagrams Connector: Generalizes/Specializes Customer Generalization is analogous to the superclass – subclass relationship among object classes. A generalizes B if B is a special case of A. Specialization is the converse of generalizes, B specializes A. NOTE: the arrow dictates how the relation should be read. « initiates » Ship Package Ship by UPS Ship by US Mail US Mail System « specializes » « generalizes » Mail Boxes, Etc. United Parcel Service See Notes *

September 28, 2005(c) Dr. David A. Workman23 Use Case Diagrams Connector: Uses Bank * Customer Uses defines a relationship where two or more use cases (or actions) share a common function or action. Shared actions need not be use cases per se, but denote significant system-level operations that can be factored to improve system performance. Also, uses should be used to relate a major use case and an optional minor system action or sub- use case. « initiates » NYSE * « uses » e-Pay Bills Buy Stock Establish Telecomm Link « uses »