University of TorontoDepartment of Computer Science© 2004-5 Steve Easterbrook. This presentation is available free for non-commercial use with attribution under a creative commons license. 1Lecture 20:Requirements Prioritization Why Prioritization is needed Basic Trade-offs Cost-Value Approach Sorting Requirements by cost/value Estimating Relative Costs/Values using AHP What if stakeholders disagree? Visualizing differences in priority Resolving DisagreementsUniversity of TorontoDepartment of Computer Science© 2004-5 Steve Easterbrook. This presentation is available free for non-commercial use with attribution under a creative commons license. 2Basics of Prioritization Need to select what to implement Customers (usually) ask for way too much Balance time-to-market with amount of functionality Decide which features go into the next release For each requirement/feature, ask: How important is this to the customer? How much will it cost to implement? How risky will it be to attempt to build it? Perform Triage: Some requirements *must* be included Some requirements should definitely be excluded That leaves a pool of “nice-to-haves”, which we must select from.University of TorontoDepartment of Computer Science© 2004-5 Steve Easterbrook. This presentation is available free for non-commercial use with attribution under a creative commons license. 3A Cost-Value Approach Calculate return on investment Assess each requirement’s importance to the project as a whole Assess the relative cost of each requirement Compute the cost-value trade-off:Cost (percent)Value (percent)Low priorityMediumpriorityHighpriority5 10 15 20 25 3051015202530Source: Adapted from Karlsson & Ryan 1997University of TorontoDepartment of Computer Science© 2004-5 Steve Easterbrook. This presentation is available free for non-commercial use with attribution under a creative commons license. 4Estimating Cost & Value Two approaches: Absolute scale (e.g. dollar values) Requires much domain experience Relative values (e.g. less/more; a little, somewhat, very) Much easier to elicit Prioritization becomes a sorting problem Comparison Process - options Basic sorting - for every pair of requirements (i,j), ask if i>j? E.g. bubblesort - start in random order, and swap each pair if out of order requires n*(n-1)/2 comparisons Construct a Binary Sort Tree Requires O(n log n) comparisons Contruct a Minimal Spanning Tree for each pair (Ri, Ri+1) get the distance between them Requires n-1 comparisonsUniversity of TorontoDepartment of Computer Science© 2004-5 Steve Easterbrook. This presentation is available free for non-commercial use with attribution under a creative commons license. 5Some complications Hard to quantify differences easier to say “x is more important than y”… …than to estimate by how much. Not all requirements comparable E.g. different level of abstraction E.g. core functionality vs. customer enhancements Requirements may not be independent No point selecting between X and Y if they are mutually dependent Stakeholders may not be consistent E.g. If X > Y, and Y > Z, then presumably X > Z? Stakeholders might not agree Different cost/value assessments for different types of stakeholderUniversity of TorontoDepartment of Computer Science© 2004-5 Steve Easterbrook. This presentation is available free for non-commercial use with attribution under a creative commons license. 6Hierarchical Prioritizationminimizecostsserve morepassengersimprovesafetyadd newtracksincreasesafe distancemore frequenttrainsincreasetrain speedminimizeoperationcostsminimizedevelopmentcostsclearersignalling Group Requirements into a hierarchy E.g. A goal tree E.g. A NFR tree Only make comparisons between branches of a single node:Bettertrain systemComparison set 1Comparison set 2Comparison set 3Comparison set 4University of TorontoDepartment of Computer Science© 2004-5 Steve Easterbrook. This presentation is available free for non-commercial use with attribution under a creative commons license. 7Analytic Hierarchy Process (AHP) Create n x n matrix (for n requirements) For element (x,y) in the matrix enter: 1 - if x and y are of equal value 3 - if x is slightly more preferred than y 5 - if x is strongly more preferred than y 7 - if x is very strongly more preferred than y 9 - if x is extremely more preferred than y (use the intermediate values, 2,4,6,8 if compromise needed) …and for (y,x) enter the reciprocal. Estimate the eigenvalues: E.g. “averaging over normalized columns” Calculate the sum of each column Divide each element in the matrix by the sum of it’s column Calculate the sum of each row Divide each row sum by the number of rows This gives a value for each reqt: …giving the estimated percentage of total value of the projectSource: Adapted from Karlsson & Ryan 1997University of TorontoDepartment of Computer Science© 2004-5 Steve Easterbrook. This presentation is available free for non-commercial use with attribution under a creative commons license. 8131/31/4Req41/311/51/2Req33513Req2421/31Req1Req4Req3Req2Req10.120.040.360.48Req40.270.180.05Req40.090.110.11Req30.450.540.63Req20.180.180.21Req1Req3Req2Req1NormalisecolumnsSumtherows0.160.620.090.340.501.980.261.05sum/4sumAHP example - estimating costsSource: Adapted from Karlsson & Ryan 1997Req1 - 26% of the costReq2 - 50% of the costReq3 - 9% of the costReq4 - 16% of the costResultUniversity of TorontoDepartment of Computer Science© 2004-5 Steve Easterbrook. This presentation is available free for non-commercial use with attribution under a creative commons license. 9Plot ROI graphCost (percent)Value (percent)Low priorityMediumpriorityHighpriority5 10 15 20 25 3051015202530xxxxx Do AHP process twice: Once to estimate relative value Once to estimate relative cost Use results to calculate ROI ratio:Source: Adapted from Karlsson & Ryan 1997University of TorontoDepartment of Computer Science© 2004-5 Steve Easterbrook. This presentation is available free for non-commercial use with attribution under a creative commons license. 10Other selection criteria ROI ratio is not the only way to group requirementsCost (percent)Value (percent)Above average costBelow average valueAbove averagein both cost and value5 10 15 20 25 3051015202530xxxxxRelative
View Full Document
Unlocking...