2004 John MylopoulosGoal Diagrams -- 1Information Systems Analysis and Design CSC340V. Goal DiagramsV. Goal DiagramsGoals and AND/OR TreesGoals and AND/OR TreesSoftgoalsSoftgoalsBuilding Goal DiagramsBuilding Goal DiagramsHow and Why QuestionsHow and Why Questions 2004 John MylopoulosGoal Diagrams -- 2Information Systems Analysis and Design CSC340GoalsGoalsI Goals represent business objectives for the new systemand its operating environment.I For example, “Fulfill every book request” (Library organization) “Produce 1M MacG5s within a year” (Apple), or, “Serve more passengers” (TTC) 2004 John MylopoulosGoal Diagrams -- 3Information Systems Analysis and Design CSC340SchedulemeetingCollectconstraintsCollecttimetablesCollect other constraintsShare timetablesSystemcollectsPersoncollectsBy emailBy all meansFrom allFromInitiatoronlyManuallyAutomaticallyInteractivelyGeneratescheduleAND decompositionOR decomposition 2004 John MylopoulosGoal Diagrams -- 4Information Systems Analysis and Design CSC340Alternatives for Satisfying GoalsAlternatives for Satisfying GoalsI An AND-goal is satisfied if all of its subgoals are; anOR-goal is satisfied if at least one its subgoals is.I An alternative (solution) to a root goal G consists ofa set of leaf goals which together satisfy G.I There are 24 alternatives for the goal of the previousslide. 2004 John MylopoulosGoal Diagrams -- 5Information Systems Analysis and Design CSC340SoftgoalsSoftgoalsI These are goals that are used as criteria for comparingalternative solutions for other goals.E.g.,Higher profits[ProductionUnit3],Better service, Satisfied customer,User-friendly[Interface2], Portable[Module4] 2004 John MylopoulosGoal Diagrams -- 6Information Systems Analysis and Design CSC340Programmability++++Allow Change of ColoursAllow Change ofStateAllow Change ofLanguageErrorAvoidanceInformationSharingEase ofLearningUserTailorabilityUsabilityUser-DefinedWriting ToolModularityUseComponentsUserFlexibilityAllow Change ofSettings+++ 2004 John MylopoulosGoal Diagrams -- 7Information Systems Analysis and Design CSC340Goal RelationshipsGoal RelationshipsI We will use more than AND- and OR-relationships: + -- one goal contributes positively towards thefulfillment of another goal; - -- one goal contributes negatively towards thefulfillment of another goal; ++ (--) -- one goal subsumes/negates another, I.e., ifthe first goal is fulfilled, the second is fulfilled/denied;I With these enhancements, we can build goal modelswhich could be useful for strategic business analysis orrequirements analysis. 2004 John MylopoulosGoal Diagrams -- 8Information Systems Analysis and Design CSC340Alternatives for Satisfying GoalsAlternatives for Satisfying GoalsI An alternative (solution) to the fulfillment of a goal Gconsists of one or more leaf goals which togetherfulfill the root goal.I A goal model defines a space of alternatives for thefulfillment of its root goal.I An alternative A1 is better than A2 in fulfilling goalG with respect to softgoals G1, G2,… if A1’s netcontributions to G1, G2,… (e.g., positive minusnegative contributions) is greater than that of A2.I In general, goals and softgoals can be contradictory.Given a set of root goals and softgoals, there may notbe an optimal solution [Simon68]. Hence the searchfor good-enough solutions. 2004 John MylopoulosGoal Diagrams -- 9Information Systems Analysis and Design CSC340Building Goal DiagramsBuilding Goal DiagramsI Start from one or more goals and/or softgoalsG1,G2,…,Gn which need to be fulfilled together.I Analyze each, looking for ways to fulfill it through AND-or OR-decompositions, or through other refinementswhich contribute positively (How questions).I Continue this process until there is enough positivesupport to fulfill all root nodes. At this point you have ndisconnected goal trees T(G1), T(G2),…,T(Gn).I Identify positive and negative inter-tree influences, I.e.,positive or negative relationships between goals g, g’which belong to different goal trees.I Repeat the analysis to see if root goals are fulfilled; if so,done, else continue the analysis. 2004 John MylopoulosGoal Diagrams -- 10Information Systems Analysis and Design CSC340Flexibility-+--UsePasswordsAvailabilityDo Backups+++++Security+ConfidentialityUsabilityIntegrityMaintenabilityRecoverabilityPerformanceMinimizeexternalcommunicationMinimizeredundancyAccuracyExtratesting 2004 John MylopoulosGoal Diagrams -- 11Information Systems Analysis and Design CSC340Softgoals Softgoals as Criteriaas CriteriaSchedulemeetingBy all meansBy email--++++--CollecttimetablesBy personBysystemHave updatedtimetablesCollectthemChoosescheduleManuallyAutomaticallyMatchingeffortCollectioneffortMinimalconflictsDegree ofparticipation Quality ofscheduleMinimaleffort 2004 John MylopoulosGoal Diagrams -- 12Information Systems Analysis and Design CSC340Library GoalsLibrary GoalsSatisfy everybook requestLimited loanperiodAs manycopies asneededEnough copiesRegularavailabilityAvailability notified 2004 John MylopoulosGoal Diagrams -- 13Information Systems Analysis and Design CSC340Public Transit GoalsPublic Transit GoalsServe morepassengersMin time between stationsMinimizecostsMin developcostsMin operatingcostsMoretracks--Trains moreclosely spaced+ 2004 John MylopoulosGoal Diagrams -- 14Information Systems Analysis and Design CSC340Why QuestionsWhy QuestionsMin operatingcostsPassengercomfortSmoothmovementWhy do weneed smoothmovement? 2004 John MylopoulosGoal Diagrams -- 15Information Systems Analysis and Design CSC340Min equipmentstressMin powerusageMin
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