Information Systems Analysis and Design CSC340 Information Systems Analysis and Design Goals V Goal Diagrams I Goals and AND OR Trees Softgoals Building Goal Diagrams How and Why Why Questions Questions I 2004 John Mylopoulos Goal Diagrams 1 Information Systems Analysis and Design CSC340 AND decomposition I Collect other constraints Interactively Manually Automatically System collects From all Goal Diagrams 2 Information Systems Analysis and Design I Share timetables Person collects 2004 John Mylopoulos CSC340 Alternatives for Satisfying Goals Goals Generate schedule Collect constraints Collect timetables Goals represent business objectives for the new system and its operating environment For example Fulfill every book request Library organization Produce 1M MacG5s within a year Apple or Serve more passengers TTC Schedule meeting OR decomposition CSC340 I An AND goal is satisfied if all of its subgoals are an OR goal is satisfied if at least one its subgoals is An alternative solution to a root goal G consists of a set of leaf goals which together satisfy G There are 24 alternatives for the goal of the previous slide From Initiator only By all means By email 2004 John Mylopoulos Goal Diagrams 3 Information Systems Analysis and Design CSC340 2004 John Mylopoulos Goal Diagrams 4 Information Systems Analysis and Design CSC340 Usability Softgoals I These are goals that are used as criteria for comparing alternative solutions for other goals E g Higher profits ProductionUnit3 Better service Satisfied customer User friendly Interface2 Portable Module4 User Tailorability Error Avoidance Information Sharing Ease of Learning User Flexibility Allow Change of Settings Programmability Modularity Allow Change of Colours Allow Change of State 2004 John Mylopoulos Goal Diagrams 5 2004 John Mylopoulos Allow Change of Language Use Components User Defined Writing Tool Goal Diagrams 6 Information Systems Analysis and Design CSC340 Information Systems Analysis and Design Alternatives for Satisfying Goals Goals Goal Relationships I We will use more than AND and OR relationships one goal contributes positively towards the fulfillment of another goal one goal contributes negatively towards the fulfillment of another goal one goal subsumes negates another I e if the first goal is fulfilled the second is fulfilled denied With these enhancements we can build goal models which could be useful for strategic business analysis or requirements analysis I CSC340 2004 John Mylopoulos Goal Diagrams 7 Information Systems Analysis and Design CSC340 I I I I An alternative solution to the fulfillment of a goal G consists of one or more leaf goals which together fulfill the root goal A goal model defines a space of alternatives for the fulfillment of its root goal An alternative A1 is better than A2 in fulfilling goal G with respect to softgoals G1 G 2 if A1 s net contributions to G1 G2 e g positive minus negative contributions is greater than that of A2 In general goals and softgoals can be contradictory Given a set of root goals and softgoals there may not be an optimal solution Simon68 Hence the search for good enough solutions 2004 John Mylopoulos Goal Diagrams 8 Information Systems Analysis and Design CSC340 Building Goal Diagrams Security Maintenability Usability I I I I I Start from one or more goals and or softgoals G1 G2 Gn which need to be fulfilled together Analyze each looking for ways to fulfill it through ANDor OR decompositions or through other refinements which contribute positively How questions Continue this process until there is enough positive support to fulfill all root nodes At this point you have n disconnected goal trees T G 1 T G2 T G n Identify positive and negative inter tree influences I e positive or negative relationships between goals g g which belong to different goal trees Repeat the analysis to see if root goals are fulfilled if so done else continue the analysis 2004 John Mylopoulos Goal Diagrams 9 Information Systems Analysis and Design CSC340 Collection effort Minimize redundancy Recoverability Extra testing Use Passwords Minimize external communication Do Backups Flexibility Performance 2004 John Mylopoulos Goal Diagrams 10 Information Systems Analysis and Design CSC340 Library Goals Satisfy every book request Limited loan period Choose schedule By system Manually Automatically By email 2004 John Mylopoulos Confidentiality Schedule meeting As many copies as needed Collect timetables By person By all means Availability Degree of participation Minimal conflicts Matching effort Integrity Accuracy Softgoals as Criteria Quality of schedule Minimal effort Have updated timetables Enough copies Availability notified Regular availability Collect them Goal Diagrams 11 2004 John Mylopoulos Goal Diagrams 12 Information Systems Analysis and Design CSC340 Information Systems Analysis and Design Public Transit Goals Serve more passengers Trains more closely spaced Why Questions Minimize costs Passenger comfort Min operating costs More tracks Min develop costs Why do we need smooth movement Min operating costs Smooth movement Min time between stations 2004 John Mylopoulos Goal Diagrams 13 Information Systems Analysis and Design CSC340 Passenger comfort Min operating costs Min equipment stress Min power usage Smooth movement 2004 John Mylopoulos CSC340 Goal Diagrams 15 2004 John Mylopoulos Goal Diagrams 14
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