Information Systems Analysis and Design csc340 IX Use Cases The Unified Modeling Language Actors and Use Cases How to Find Them 2004 John Mylopoulos Use Cases 1 Information Systems Analysis and Design csc340 The Unified Modeling Language UML Booch and Rumbaugh started working towards a unified modelling language UML in 1994 under the auspices of Rational Inc They were later joined by Jacobson UML only offers a notation not a methodology for modeling as various OOA techniques do Combines Jacobson s use cases with Booch and Rumbaugh concepts for object modeling along with statecharts UML has been adopted by the Object Management Group OMG as an object modelling standard OMG UML 1 0 is the first version of this new modelling standard 2004 John Mylopoulos Use Cases 2 Page Information Systems Analysis and Design csc340 Where Do We Start Use Cases Use cases describe how the system to be or any artifact under design for that matter from a user s perspective They answer the question How will the artifact be used once it is built Used to show the functions to be supported Developed by Ivar Jacobson and friends Jacobson92 2004 John Mylopoulos Use Cases 3 Information Systems Analysis and Design csc340 Actors An actor is anything that needs to exchange information with the artifact An actor could be a person or another external system Actors define roles that users can play while using the artifact Campaign Manager Staff Contact Accountant 2004 John Mylopoulos Use Cases 4 Page Information Systems Analysis and Design csc340 Use Cases A use case is a function the new system needs to support Each use case is a sequence of steps performed by an actor and the system through a dialogue To find use case examine each actor and her needs Add new client Record client payment Change a client contact 2004 John Mylopoulos Use Cases 5 Information Systems Analysis and Design csc340 Use Case Diagrams Use case diagrams are created to capture the relationships between actors and use cases Change a client contact Campaign Manager Staff contact Add a new client Record client payment Accountant 2004 John Mylopoulos Use Cases 6 Page Information Systems Analysis and Design csc340 Notation for Use Cases Use case Change client contact Staff contact Actor Communication System Artifact association boundary 2004 John Mylopoulos Use Cases 7 Information Systems Analysis and Design csc340 Agate is an Advertising Company which puts together advertising campaigns for client companies Here is the breakdown of their staff Direction Admin Campaigns Mgt 1 Campaign 1 Creative 1 Admin 1 Finance 1 Office mgr 3 Direction asst 4 Manager clerks 2 Receptionists 2 Clerks typists 2 Campaign managers 3 Campaign marketers 1 Editor in Chief 1 Creative Manager Edition 1 Filing clerk 2 Editors 4 Copy writers Graphics 6 Graphic designers 2 Photographers IT 1 IT manager 1 Network administrator 1 System admin 1 Analyst Accounts Edition 1 Accountant manager 1 Credit controller 2 Accounts clerks 2 Purchasing assistants 2004 John Mylopoulos Documentation 1 Media librarian 1 Resource libr 1 Knowledge worker 1 Computer tech Use Cases 8 Page Information Systems Analysis and Design csc340 Add new staff member Add new staff grade Agate Case Study Change rate for staff grade Accountant Change grade for staff member Calculate staff bonuses 2004 John Mylopoulos Use Cases 9 Information Systems Analysis and Design csc340 extends and uses extends used to model a part of a use case that the user may see as optional system behavior also models a separate sub case which is executed conditionally uses adds behavior to a base case like a procedure call extends Check Campaign Budget Check Political Campaign Budget uses Find Campaign 2004 John Mylopoulos Use Cases 10 Page Information Systems Analysis and Design csc340 Finding Actors Actors can be identified by answering the following Who will be a primary user of the artifact Who will be supported Who will maintain administrate the artifact What hardware does the system need Which other systems does it interact with Who or what has an interest in the results that the artifact produces Tip don t consider only the users who directly use the artifact but also others who need services from the artifact 2004 John Mylopoulos Use Cases 11 Information Systems Analysis and Design csc340 Finding Use Cases For each actor ask the following questions Which functions does the actor require from the artifact What does the actor need to do Does the actor need to read create destroy modify or store some kinds of information in the artifact Does the actor have to be notified about events in the artifact Or does the actor need to notify the artifact about something What do those events require in terms of artifact functionality Could the actor s daily work be simplified or made more efficient through new functions provided by the artifact 2004 John Mylopoulos Use Cases 12 Page Information Systems Analysis and Design csc340 Documenting Use Cases For each use case prepare a flow of events document written from an actor s point of view The document details what the system must provide to the actor when the use case is executed Typical contents How the use case starts and ends Normal flow of events Alternate flow of events Exceptional flow of events 2004 John Mylopoulos Use Cases 13 Information Systems Analysis and Design csc340 Use Cases for a Meeting Scheduling System Initiator ValidateUser Participant uses extends Provide Generate uses Withdraw Constraints Schedule Edit ScheduleMtg Constraints 2004 John Mylopoulos Use Cases 14 Page Information Systems Analysis and Design csc340 Use Cases for a Car Driver Mechanic GasAttendant FixCar Drive uses FillUp TurnOnEngine uses uses extends CheckOil FixCarOntheRoad 2004 John Mylopoulos Use Cases 15 Information Systems Analysis and Design csc340 Additional Readings Booch99 Booch G et al The Unified Modeling Language User Guide Chapters 2 16 17 Addison Wesley 1999 Jacobson92 Jacobson I et all Object Oriented Software Engineering A Use Case Driven Approach Addison Wesley 1992 Schneider98 Schneider G et al Applying Use Cases Addison Wesley 1998 2004 John Mylopoulos Use Cases 16 Page
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