Quản lí dự án - Chapter 5: Scheduling the project

Chapter 5Scheduling the ProjectIntroductionProject schedule is the project plan in an altered formatIt is a convenient form for monitoring and controlling project activitiesCan be prepared in several formatsGantt chartsPERT networkCPM networkPERT and CPM NetworksPERT and CPM developed independently in 1950’sProgram Evaluation and Review Technique (PERT)U.S. Navy, Booz-Allen Hamilton, and Lockheed AircraftProbabilistic activity durationsCritical Path Method (CPM)Dupont De Nemours Inc.Deterministic activity durationsThe Language of PERT/CPMActivityA task or set of tasksUses resources and timeEventAn identifiable state resulting from completion of one or more activitiesConsumes no resources or timePredecessor activities must be completedMilestonesIdentifiable and noteworthy events that mark significant progressThe Language of PERT/CPM ContinuedNetworkA diagram of nodes (activities or events) and arrows (directional arcs) that illustrate the technological relationships of activitiesPathA series of connected activities between two eventsCritical pathThe set of activities on a path that, if delayed, will delay the completion date of the projectCritical TimeThe time required to complete all activities on the critical pathBuilding the NetworkThere are two ways of displaying a project networkActivities on arrows (AOA) networkThe activities are shown as arrows and events as nodesGenerally more difficult to draw but depicts the technical relationships of the activities wellActivities on nodes (AON) networkEach task is shown as a node and the technological relationship is shown by the arrowsAON network usually associated with CPMAOA network usually associated with PERTSample AON NetworkTable 5-1Figure 5-3Sample AOA NetworkTable 5-1Figure 5-6 (a)Which to Use?Mostly AON used throughout this textbookAON used by most of the popular softwareAON networks are easier to draw by handLarge (20+ activities) AOA networks are difficult to drawSoftware to draw AOA networks is expensiveFinding the Critical Path and Critical TimeES: Earliest start timeEF: Earliest finish timeLS: Latest start timeLF: Latest finish timeDisplayed on node as shownES + completion = EFLS + completion = LFFigure 5-9A Sample Problem for Finding the Critical Path and Critical TimeTable 5-2The Complete NetworkTable 5-2 and Figure 5-8The Critical Path and Completion Time for Sample ProjectFigure 5-10Notes on Sample ProjectAll activities, and thus all paths, must be completed to finish the projectThe shortest time for completion of the network is equal to the longest path through the networkIn this case a-e-h-jIf any activity on this path is even slightly delayed, the project will be delayedCalculating Activity SlackES: Earliest start timeEF: Earliest finish timeLS: Latest start timeLF: Latest finish timeSlack = LS – ESSlack = LF – EFEither method of calculating slack gives the same resultsManagerial ImplicationsThe primary attention of the project manager must be to activities on the critical pathIf anything delays one of these activities, the project will be lateProjects are easier to manage when there is project slackDoing It the Easy Way—Microsoft Project (MSP)Data is entered using a tab entry tableShown on next slideMSP automatically numbers each activityMSP has numerous options for viewing the dataMSP automatically draws an AON networkShown on later slideA Microsoft Project Version of Data in Table 5-2Table 5-3A Microsoft Project Version of the PERT/CPM Network from Table 5-3Figure 5-11Calculating Probabilistic Activity TimesFigure below shows distribution of all possible durations for some taskEstimate a is such that the actual duration of the task will be a or lower less than 1 percent of the timeEstimate b is such that the actual finish time will be b or greater less than 1 percent of the timeEstimate m is the most likely timeFigure 5-13Activity Expected Time and Variance95 Percent LevelTask will be a or lower 5 percent of the timeTask will be b or greater 5 percent of the time90 Percent LevelTask will be a or lower 10 percent of the timeTask will be b or greater 10 percent of the timeThe Probabilistic NetworkExpected time (TE) for each activity is calculatedVariance (σ2) for each activity is calculatedTE for each activity is used to find the critical path and critical time for the networkSlack is calculated in the usual fashionThe variance (σ2) of a path is the sum of the activity variances for that pathStandard deviation (σ) is the square of the varianceThe Probabilistic Network, an ExampleTable 5-4Is it Really the Critical pathGiven uncertainty, cannot be sure that any specific path is the critical path“Critical” path may take less than expected while another path takes longerOnly after the fact do we know which path was actually criticalManagerial implication is the project manager must carefully manage all paths that have a reasonable probability of becoming criticalOnce More the Easy WayMicrosoft Project can easily handle the probabilistic networkHowever, it does not perform some of the calculationsThese can be done in ExcelMicrosoft Project calculates using a calendar rather than daysUses a real-world calendar including weekends and holidaysThe Probability of Completing the Project on TimeCan the project be completed in X days?Can be answered with the information available concerning the level of uncertainty for the various project activitiesAssumes activities are statistically independentTo complete a project by a specified time requires that all the paths in the network be completed by the specified timeThe Probability of Completing the Project on Time ContinuedDetermining the probability that a project is completed by a specified time requires calculating the probability that all paths are finished by the specified timeWe then calculate the probability that the entire project is completed within the specified time by multiplying these probabilities togetherThis requires the assumption that the paths are statistically independentCalculating Path ProbabilityD = desired project completion time50 in this exampleμ = the sum of the TE activities on the path being investigated47 in this exampleσ2u = the variance of the path being consideredA Z of 1.10 yields a probability of 0.8643 or 86 percentTable 5-4The Statistical Distribution of the Completion Times for ExampleFigure 5-18Selecting Risk and Finding DSimulationSimulation is a different approach to managing riskBuilds on the probabilistic functions already discussedHelps to understand the consequences of uncertaintyProvides insight into the range and distribution of project completion timesCrystal Ball Chart for Project Completion TimeFigure 5-19Traditional Statistics vs. SimulationBoth approaches assume that task times are statistically independentBoth approaches assume the paths are independentA simulation can circumvent the assumption of statistical independence by including the activity or path dependencies as part of the modelSimulation requires less computational effortThe Gantt ChartHenry Gantt developed the Gantt chart around 1917It displays project activities as bars measured against a horizontal time scaleMost popular way of exhibiting sets of related activities in the form of schedulesThe ChartGantt charts are easy to drawProblems arise when several tasks begin at the same time and have the same durationCan make it hard to find critical pathOnly a problem on hand-drawn chartsSoftware shows critical path using some visual methodEven with software, technical dependencies are harder to see on a Gantt chartA Gantt Chart of a Sample ProjectFigure 5-21A Gantt Chart Showing Critical Path, Path Connections, Other DataFigure 5-22Extensions to PET/CPMApplication of fuzzy set theory to aid in estimating activity durationsExtensions to precedence diagrammingGoldratt’s Critical ChainPrecedence DiagrammingFinish to start (F to S)Finish of Activity A to start of Activity BStart to start (S to S)Start of Activity A to start of Activity B Finish to finish (F to F)Finish of Activity A to finish of Activity BStart to finish (S to F)Start of Activity A to finish of Activity BPrecedence Diagramming ConventionsFigure 5-25CopyrightCopyright © 2014 John Wiley & Sons, Inc.All rights reserved. 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