PM Chapter5

Chapter 5:Project Time Management2Learning ObjectivesExplain the basic process for developing project schedulesDescribe how various tools and techniques help project managers perform activity definition, activity sequencing, activity duration estimating, schedule development, and schedule controlUse a Gantt chart for schedule planning and tracking schedule informationConstruct a project network diagram and understand its importance for determining overall project completion dates Understand and use critical path analysisDescribe several techniques for shortening project schedules Explain the basic concepts behind critical chain schedulingDiscuss reality checks and people issues involved in project schedule management and controlDescribe how software can assist in project time management3Chapter OutlineImportance of Project SchedulesWhere Do Schedules Come From? Defining ActivitiesActivity SequencingProject Network Diagrams Activity Duration EstimatingSchedule Development Gantt ChartsCritical Path MethodProgram Evaluation and Review Technique (PERT)Controlling Changes to the Project Schedule Reality Checks on Scheduling Working with People IssuesUsing Software to Assist in Time ManagementWords of Caution On Using Project Management Software1. Importance of Project Schedules5Importance of Project SchedulesManagers often cite delivering projects on time as one of their biggest challengesAverage time overrun from 1995 CHAOS report was 222%; improved to 63% in 2001 studyTime has the least amount of flexibility; it passes no matter whatSchedule issues are the main reason for conflicts on projects, especially during the second half of projects6Conflict Intensity Over the Life of a Project0.000.050.100.150.200.250.300.350.40Project FormationEarly Phases Middle PhasesEnd PhasesC o n f l i c t I n t e n s i t ySchedulesPriorities Manpower Technical opinions Procedures CostPersonality conflictsAverage Total Conflict7Project Time Management ProcessesProject time management involves the processes required to ensure timely completion of a project. Processes include:Activity definition Activity sequencingActivity duration estimating Schedule developmentSchedule control2.Where Do Schedules Come From?9Defining ActivitiesProject schedules grow out of the basic document that initiate a projectProject charter includes start and end dates and budget informationScope statement and WBS help define what will be doneActivity definition involves developing a more detailed WBS and supportingexplanations to understand all the work to be done3.Activity Sequencing11Activity SequencingInvolves reviewing activities and determining dependenciesMandatory dependencies : inherent in the nature of the work; hard logicDiscretionary dependencies : defined by the project team; soft logicExternal dependencies : involve relationships between project and non-project activitiesExamples of each type of dependency from your team projects?You must determine dependencies in order to use critical path analysis12Project Network DiagramsProject network diagrams are thepreferred technique for showing activity sequencingA project network diagram is a schematic display of the logicalrelationships among, or sequencing of, project activities13Sample Activity-on-Arrow (AOA) Network Diagram for Project X14Arrow Diagramming Method (ADM)Also called activity-on-arrow (AOA) project network diagramsActivities are represented by arrowsNodes or circles are the starting and ending points of activitiesCan only show finish-to-start dependencies15Process for Creating AOA Diagrams1. Find all of the activities that start at node 1. Draw their finish nodes and draw arrows between node 1 and those finish nodes. Put the activity letter or name and duration estimate on the associated arrow2. Continuing drawing the network diagram, working from left to right. Look for bursts and merges. Bursts occur when a single node is followed by two or more activities. A merge occurs when two or more nodes precede a single node3. Continue drawing the project network diagram until all activities are included on the diagram that have dependencies4. As a rule of thumb, all arrowheads should face toward the right, and no arrows should cross on an AOA network diagram16Precedence Diagramming Method (PDM)Activities are represented by boxesArrows show relationships between activitiesMore popular than ADM method and used by project management softwareBetter at showing different types of dependencies17Task Dependency Types18Sample PDM Network Diagram for Project XProject 2000 file4. Activity Duration Estimating20Duration EstimatingAfter defining activities and determining their sequence, the next step in time management is duration estimatingDuration includes the actual amount of time worked on an activity plus elapsed timeExamples of duration estimates toRead a favorite book?Prepare your team ’s final presentation?People doing the work should help create estimates, and an expert should review them5.Schedule Development22Schedule DevelopmentSchedule development uses results of the other time management processes to determine the start and end date of the project and its activitiesUltimate goal is to create a realistic project schedule that provides a basis for monitoring project progress for the time dimension of the projectImportant tools and techniques include Gantt charts, PERT analysis, critical path analysis, and critical chain scheduling23制定进度计划的重要方法、技术与工具甘特图与网络图甘特图(Gantt Chart)的构造网络图(Network Diagram)的构造用MS Project 构造甘特图与网络图分析项目网络图的关键路径关键路径(Critical Path )参数分析PERT随机活动历时的关键路径模拟分析24项目网络图的关键路径分析项目的关键路径(Project Critical Path)是指一系列决定项目最早完成时间的活动是网络图中最长的路径,并且有最少的浮动时间或时差关键路径法(Critical Path Method-CPM)是一种用来预测总体项目历时的项目网络分析技术25确定关键路径*计算最长路径计算如下参数ES,EF---向前递推 LS,LF---向后递推利用总时差决定关键路径26分析关键路径方法一：路径穷举27思考如下的项目网络图. 假设所有的时间都以天为单位.2345A=2B=5C=2D=716F=2E=1startfinisha. 该网络图中共有多少条路径?b. 每条路径有多长?c. 哪一条是关键路径?d. 完成本项目最短需要多长时间?28为某项目确定关键路径29分析关键路径方法二:参数标号法最早开始时间ES 最早结束时间EF 最迟开始时间LS 最迟结束时间LF 总时差TF自由时差FF网络计划时间参数30第一类参数ES (Early Start),EF (Early Finish)由前向后递推(箭头方向)EF=Max(ES 1+t 1,ES 2+t 2…)最早开始时间ESES ＝MAX{紧前工作的EF}最早结束时间EFEF ＝ES ＋工作延续时间t31A 3E 8C 7 F 6D 4B 2G 5代号时间示例：最早参数计算(练习)32A 3E 8C 7 F 6D 4B 2G 5代号时间示例：033531037101810161823最早参数计算(练习答案)33第二类参数LS (Lately Start),,LF (lately Finish) 由后向前递推LS=Min(LF 1-t 1,EF 2-t 2…)最迟结束时间LFLF ＝MIN{紧后工作的LS}最迟开始时间LSLS ＝LF—工作延续时间t34A 3E 8C 7 F 6D 4B 2G 5代号时间示例：033531037101810161823最迟参数计算(练习)35A 3E 8C 7 F 6D 4B 2G 5代号时间示例：0335310371018101618232318181218101281031083最迟参数计算(练习答案)36时差(机动时间)计算总时差的计算总时差＝LF—EF或总时差＝LS—ES自由时差自由时差＝min{ES(紧后工作)} —EF37自由浮动时间或自由时差是指一项活动在不耽误后继活动的最早开始时间的情况下,可以延迟的长度只有在有两项或以上的活动指向同一活动时才存在自由时差总浮动时间或总时差是指在不拖延项目计划完成日期的情况下,一项活动从其最早开始时间算起,可以被拖延的时间38A 3E 8C 7 F 6D 4B 2G 5代号时间示例：0335310371018101618232318181218101281031083时差(机动时间)计算(练习)39A 3E 8C 7 F 6D 4B 2G 5代号时间示例：033531037101810161823231818121810128103108305050200203050时差(机动时间)计算(练习答案)40关键路径法补充说明如果关键路径上的一个或多个活动历时增加,则这个项目完成时间将会增加,除非采取相应的调整措施容易理解错误的地方:关键路径不是包括所有最重要活动的路径,它只与项目的时间维度有关如果两条或多条路径的长度相同,则关键路径可能不唯一关键路径可能随着项目进展而改变41总工期=MAX （活动最大的最早结束时间）总时差：活动不改变计划总工期的机动时间活动在总时差的范围内调整不影响项目的总工期总时差最小的活动是关键活动关键活动组成的路径是关键路径关键路径是工期最长（等于总工期）的路径自由时差：活动不改变紧前紧后活动的计划安排的机动时间活动在自由时差的范围内调整对项目计划没有影响42网络计划时间参数计算(复习)最早开始时间ES ＝MAX{紧前工作的EF 最早结束时间EF ＝ES ＋工作延续时间t 最迟结束时间LF ＝MIN{紧后工作的LS} 最迟开始时间LS ＝LF—工作延续时间t 总时差TF ＝LF—EF ＝LS—ES自由时差FF= min{ES(紧后工作)}-EF43搭接网络的时间参数计算结束—开始(FTS):最早时间:ES j =EF i +FTS EF j =ES j +D j 最迟时间:LF i =LS j −FTS LS i =LF i −D iiFTSj自由时差:FF i =ES j −FTS −EF i44搭接时的参数计算（FST ）19910154530？24626420FS545网络参数计算(练习)A 3E 8C 7 F 6D 4B 2G 5代号时间示例：SS4FS8FF34603310351115715A 3E 8B 2F 6D 4C 7G 5SS 4FS 8FF 3152115242419211519111511119157304604000402001914有搭接情况的网络参数计算(练习答案)47Gantt ChartsGantt charts provide a standard format fordisplaying project schedule information by listing project activities and theircorresponding start and finish dates in a calendar formatSymbols include:A black diamond: milestones or significant events on a project with zero duration Thick black bars: summary tasks Lighter horizontal bars: tasksArrows: dependencies between tasks48Gantt Chart for Project XProject 2000 file49Gantt Chart for Software Launch ProjectProject 2000 file50Sample Tracking Gantt Chartwhite diamond: slipped milestone two bars: planned and actual times51Critical Path Method (CPM)CPM is a project network analysistechnique used to predict total project durationA critical path for a project is the series of activities that determines the earliest time by which the project can be completedThe critical path is the longest path through the network diagram and has the least amount of slack or float52Finding the Critical PathFirst develop a good project network diagramAdd the durations for all activities on each path through the project network diagramThe longest path is the critical path53Simple Example of Determining the Critical PathConsider the following project network diagram. Assume all times are in days.2345A=2B=5C=2D=716F=2E=1startfinisha. How many paths are on this network diagram?b. How long is each path?c. Which is the critical path?d. What is the shortest amount of time needed to complete this project?54Determining the Critical Path for Project X55More on the Critical PathIf one of more activities on the critical path takes longer than planned, the whole project schedule will slip unless corrective action is takenMisconceptions:The critical path is not the one with all the critical activities; it only accounts for timeThere can be more than one critical path if the lengths of two or more paths are the sameThe critical path can change as the project progresses56Using Critical Path Analysis to Make Schedule Trade-offsKnowing the critical path helps you make schedule trade-offsFree slack or free float is the amount of time an activity can be delayed without delaying the early start of any immediately following activitiesTotal slack or total float is the amount of time an activity may be delayed from its early start without delaying the planned project finish date57Free and Total Float or Slack for Project X58Techniques for Shortening a Project ScheduleShortening durations of critical tasks for adding more resources or changing their scopeCrashing tasks by obtaining the greatest amount of schedulecompression for the least incremental costFast tracking tasks by doing them in parallel or overlapping them59Shortening Project SchedulesOverlapped Tasks or fast trackingShortened duration thru crashingOriginal schedule60Project Cost-Time Graph61Activity Graph 62Cost-Time Trade-Off Example63Cost-Time Trade-Off Example (continued)6465Project Cost-Time Graph66Importance of Updating Critical Path DataIt is important to update project schedule informationThe critical path may change as you enter actual start and finish datesIf you know the project completion date will slip, negotiate with the project sponsor67Program Evaluation and Review Technique (PERT)PERT is a network analysis technique used to estimate project duration when there is a high degree of uncertainty about the individual activity duration estimatesPERT uses probabilistic time estimates based on using optimistic, most likely, and pessimistic estimates of activity durations68PERT Formula and ExamplePERT weighted average formula:optimistic time + 4X most likely time + pessimistic time6Example:PERT weighted average =8 workdays + 4 X 10 workdays + 24 workdays = 12 days 6where 8 = optimistic time, 10 = most likely time, and 24 = pessimistic time69计划评审技术(PERT)计划评审技术(Program Evaluationand Review Technique, PERT)当具体活动历时估算存在很大的不确定性时,用来估计项目历时的网络分析技术PERT 方法要回答如下问题：在得到了对每个活动工期的不确定估计情况下，项目在某一期限内完成的概率是多少？70PERT 的时间估计模式最大可能估计(most probable):完成某项活动最可能出现的工期估计乐观估计(optimistic):在最佳条件下完成某活动的工期估计悲观估计(pessimistic ):在最不利条件下完成某活动的工期估计71三种估计的概率分布模型d : expected durations : standard deviationp : parameter (usually 6)pa - b= s ,6b + 4m + a = d 72例1:一项活动的乐观时间为1周，最可能时间为5周，悲观时间为15周，这项活动的期望工期和方差为：6615541=+×+=e t 其β概率分布如图所示:1t 05t m 6t e 15t p概率时间有关参数的计算1. 活动的工期和方差的估计44.5)6115(22=−=σ73例2:另一活动的乐观时间为10周，最可能时间为15周，悲观时间为20周，这项活动的期望工期为：1562015410=+×+=e t 其β概率分布如图所示:10t o15t e20t p时间概率78.2)61020(22=−=σ74曲线的峰值代表了每项活动各自的最可能时间。