© McGraw-Hill/Irwin 2004 Information Systems Project ManagementDavid Olson 8-1

© McGraw-Hill/Irwin 2004 Information Systems Project ManagementDavid Olson 8-2 Chapter 8: Network Scheduling Methods Critical path method (CPM) Buffers Leveling & Smoothing

© McGraw-Hill/Irwin 2004 Information Systems Project ManagementDavid Olson 8-3 why networks? Gantt charts dont explicitly show task relationships dont show impact of delays or shifting resources well network models clearly show interdependencies

© McGraw-Hill/Irwin 2004 Information Systems Project ManagementDavid Olson 8-4 Logic Diagrams network of relationships elements & relationships (sequence) this is ACTIVITY-ON-NODE can have ACTIVITY-ON-ARC research whats been done research what needs doing pick final topic internet research writeprint

© McGraw-Hill/Irwin 2004 Information Systems Project ManagementDavid Olson 8-5 Network Diagrams activity duration milestone immediate predecessors identified by arrows leading into durations can include in parentheses dummy activities need for AOA networks activity (duration) milestone

© McGraw-Hill/Irwin 2004 Information Systems Project ManagementDavid Olson 8-6 networks networks make a good visual they are TOTALLY UNNECESSARY for identifying –early startsearliest an activity can be begun –late finisheslatest an activity can finish –slackspare time –critical pathsactivities with no slack

© McGraw-Hill/Irwin 2004 Information Systems Project ManagementDavid Olson 8-7 Project Scheduling MODEL COMPONENTS activities from WBS predecessors what this activity waits on durations how long –durations are PROBABILISTIC –CPM DETERMINISTIC –PERT considers uncertainty, but UNREALISTIC –simulation all assume unlimited resources

© McGraw-Hill/Irwin 2004 Information Systems Project ManagementDavid Olson 8-8 Critical Path Method INPUTS: activities, durations, immediate predecessors ALGORITHM forward pass schedule all activities with no unscheduled predecessors ES/EF determine early starts & early finishes (start ASAP, add duration) backwards pass schedule in reverse (schedule all activities with no unscheduled FOLLOWERS) LF/LS determine late finishes, subtract duration to get late starts slack difference between LS-ES (same as LF-EF) critical path all chains of activities with no slack

© McGraw-Hill/Irwin 2004 Information Systems Project ManagementDavid Olson 8-9 CPM Example FORWARD PASS activitydurationpredecessor A requirements analysis3 weeks- B programming7 weeksA C get hardware1 weekA D train users3 weeksB, C schedule Astart0finish0+3=3 schedule B33+7=10 & C33+1=4 schedule D1010+3=13

© McGraw-Hill/Irwin 2004 Information Systems Project ManagementDavid Olson 8-10 CPM Example backward pass schedule Dfinish13late start=13-3= 10 schedule B1010-7= 3 & C1010-1= 9 schedule A33-3= 0 slackALF=3EF=33-3= 0 BLF=10EF= = 0 CLF=10EF=410-4= 6 DLF=13EF= = 0 critical path:A-B-D

© McGraw-Hill/Irwin 2004 Information Systems Project ManagementDavid Olson 8-11 Gantt Chart

© McGraw-Hill/Irwin 2004 Information Systems Project ManagementDavid Olson 8-12 CPM can have more than one critical path activitydurationpredecessor A requirements analysis3 weeks- B programming7 weeksA C get hardware7 weeksA D train users3 weeksB, C critical paths A-B-D A-C-D both with duration of 13 weeks

© McGraw-Hill/Irwin 2004 Information Systems Project ManagementDavid Olson 8-13 Buffers Assure activities completed on time (Goldratt, 1997) Project Buffers: after final project task Feeding Buffers: where non-critical activities lead into critical activities Resource Buffers: before resources scheduled to work on critical activities Strategic Resource Buffers: assure key resources available

© McGraw-Hill/Irwin 2004 Information Systems Project ManagementDavid Olson 8-14 Project Buffer

© McGraw-Hill/Irwin 2004 Information Systems Project ManagementDavid Olson 8-15 Resource Limitations critical path crashing (cost/time tradeoff) other methods

© McGraw-Hill/Irwin 2004 Information Systems Project ManagementDavid Olson 8-16 Crashing can shorten project completion time by adding extra resources (costs) start off with NORMAL TIME CPM schedule get expected duration Tn, cost Cn Tn should be longest duration Cn should be most expensive in penalties, cheapest in crash costs

© McGraw-Hill/Irwin 2004 Information Systems Project ManagementDavid Olson 8-17 Time Reduction to reduce activity time, pay for more resources develop table of activities with times and costs for each activity, usually assume linear relationship for relationship between cost & time

© McGraw-Hill/Irwin 2004 Information Systems Project ManagementDavid Olson 8-18 Crash Example Activity: programming Tn: 7 weeks Cn: $14,000 (7 weeks, 2 programmers) if you add a third programmer, done in 6 weeks Tc: 6 weeks Cn: $15,000 cost slope = ( )/(6-7)=-$1000/week

© McGraw-Hill/Irwin 2004 Information Systems Project ManagementDavid Olson 8-19 Example Problem activityPred TnCnTcCcslopemax A requirements none 3cant crash B programmingA week C get hardwareA week D train users B,C 3cant crash Crashing Algorithm: 1 crash only critical activities B only choice 2 crash cheapest currently critical B is cheapest 3 after crashing one time period, recheck critical

© McGraw-Hill/Irwin 2004 Information Systems Project ManagementDavid Olson 8-20 Crash Example Import critical software from Australia: late penalty $500/d > 12 d A get import license5 daysno predecessor B ship7 daysA is predecessor C train users11 daysno predecessor D train on system2 daysB,C predecessors can crashC: $2000/day more than current for up to 3 days B: faster boat6 days$300 more than current bush plane5 days$400 more than current commercial3 days$500 more than current

© McGraw-Hill/Irwin 2004 Information Systems Project ManagementDavid Olson 8-21 Crash Example Original schedule: 14 days, $1,000 in penalties= $1000 crash B to 6 days:13 days, $500 penalties, $300 cost = $800* crash B to 5 C to 10:12 days, no penalties, $ cost= $2400 to 11 days is worse NOW A SELECTION DECISION risk versus cost

© McGraw-Hill/Irwin 2004 Information Systems Project ManagementDavid Olson 8-22 Crashing Limitations assumes linear relationship between time and cost –not usually true (indirect costs dont change at same rate as direct costs) requires a lot of extra cost estimation time consuming ends with tradeoff decision

© McGraw-Hill/Irwin 2004 Information Systems Project ManagementDavid Olson 8-23 Resource Constraining CPM & PERT both assume unlimited resources NOT TRUE –may have only a finite number of systems analysts, programmers RESOURCE LEVELING - balance the resource load RESOURCE CONSTRAINING - dont exceed available resources

© McGraw-Hill/Irwin 2004 Information Systems Project ManagementDavid Olson 8-24 Resource Leveling unleveledleveled

© McGraw-Hill/Irwin 2004 Information Systems Project ManagementDavid Olson 8-25 Work Patterns natural resource demands tend to have lumps maintaining a stable work force works better if demand leveled HOW TO LEVEL: split each activity into smaller activities, schedule them at different times USUALLY NOT THAT EASY

© McGraw-Hill/Irwin 2004 Information Systems Project ManagementDavid Olson 8-26 Resource Leveling this leveling often works for specific activities, but complicated even more when resources shared

© McGraw-Hill/Irwin 2004 Information Systems Project ManagementDavid Olson 8-27 Resource Leveling Methods split up work, stagger eliminate some activities (subcontract) substitute less resource consuming activities (use CASE tools) substitute resources (hire spot work programmers)

© McGraw-Hill/Irwin 2004 Information Systems Project ManagementDavid Olson 8-28 Resource Smoothing Adjust schedules to level workload –expand duration for peak load –compress durations where load low Fill in gaps of work Requires balancing resources –for activities with heavier load, use multiple crews

© McGraw-Hill/Irwin 2004 Information Systems Project ManagementDavid Olson 8-29 Resource Loading MUST schedule activities to not overschedule critical resource If there is only one training room, and it includes the only delivery system –cant speed up training –cant conduct two training activities at once LINEAR PROGRAMMING heuristics

© McGraw-Hill/Irwin 2004 Information Systems Project ManagementDavid Olson 8-30 Recap cost/time tradeoff –time consuming, still makes assumptions resource leveling –manual shuffling resource constraining –pure solution to optimality a research issue –heuristics have been applied in software NO IDEAL SOLUTION METHOD

© McGraw-Hill/Irwin 2004 Information Systems Project ManagementDavid Olson 8-31 Criticisms of CPM Rarely to activities proceed as planned –critical path therefore very volatile options to speed some activities available –crashing resource limits not reflected –resource leveling schedule likely to be very lumpy –resource smoothing

© McGraw-Hill/Irwin 2004 Information Systems Project ManagementDavid Olson 8-32 Summary Critical path provides managers valuable information –What activities interfere with project completion –Estimate of project duration Buffers a means to manage risk Crashing a means to analyze cost/time tradeoff Resource management –Leveling –smoothing