Copyright 2012 John Wiley & Sons, Inc.

Chapter 8

Scheduling

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Useful Abbreviations

CPM - Critical Path MethodPERT - Program Evaluation and Review

Technique

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Background

Schedule is the conversion of a project action plan into an operating timetable

Basis for monitoring a project One of the major project management tools Work changes daily, so a detailed plan is

essential Not all project activities need to be scheduled at

the same level of detail

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Background Continued

Most of the scheduling is at the WBS level, not the work package level

Only the most critical work packages may be shown on the schedule

Most of the scheduling is based on network drawings

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Network Scheduling Advantage

Consistent frameworkShows interdependencesShows when resources are neededEnsures proper communicationDetermines expected completion date Identifies critical activities

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Network Scheduling Advantage Continued

Shows which of the activities can be delayed

Determines start datesShows which task must be coordinatedShows which task can be run parallelRelieves some conflictAllows probabilistic estimates

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Network Scheduling Techniques: PERT (ADM) and CPM (PDM)

PERT was developed for the Polaris missile/submarine project in 1958

CPM developed by DuPont during the same time

Initially, CPM and PERT were two different approaches– CPM used deterministic time estimates and allowed

project crunching– PERT used probabilistic time estimates

Microsoft Project (and others) have blended CPM and PERT into one approach

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Terminology

Activity - A specific task or set of tasks that are required by the project, use up resources, and take time to complete

Event - The result of completing one or more activities

Network - The combination of all activities and events that define a project– Drawn left-to-right– Connections represent predecessors

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Terminology Continued

Path - A series of connected activitiesCritical - An activity, event, or path

which, if delayed, will delay the completion of the project

Critical Path - The path through the project where, if any activity is delayed, the project is delayed– There is always a critical path– There can be more than one critical path

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Terminology Continued

Sequential Activities - One activity must be completed before the next one can begin

Parallel Activities - The activities can take place at the same time

Immediate Predecessor - That activity that must be completed just before a particular activity can begin

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Terminology Continued

Activity on Arrow - Arrows represent activities while nodes stand for events

Activity on Node - Nodes stand for events and arrows show precedence

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AON and AOA Format

Figure 8-3

Figure 8-2

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Constructing the Network

Begin with START activityAdd activities without precedences as

nodes– There will always be one– May be more

Add activities that have those activities as precedences

Continue

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Gantt (Bar) Charts

Developed by Henry L. GanttShows planned and actual progressEasy-to-read method to know the current

status

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Advantages and Disadvantage

Advantages– Easily understood– Provide a picture of the current state of a

projectDisadvantage

– Difficult to follow complex projects

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Microsoft Project Gantt Chart

Figure 8-11

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Microsoft Project AON Network

Figure 8-12

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Solving the Network

Table 8-1

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The AON Network from the previous table

Figure 8-13

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Calculating Activity Times

2

22

6

6

4

ab

bmaTE

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The Results

Table 8-2

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Critical Path and Time

Figure 8-15

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Critical Path and Time Continued

Figure 8-16

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Slack

Figure 8-16

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Slack Values

Table 8-3

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Precedence Diagramming

Finish to startStart to startFinish to finishStart to finish

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Precedence Diagramming Conventions

Figure 8-17

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Microsoft Projects

Table 8-4

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Gantt Chart

Figure 8-18

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AON Network

Figure 8-19

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Microsoft Project Calendar

Figure 8-23

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Uncertainty of Project Completion Time

Assume activities are statistically independent

Variance of a set of activities is the sum of the individual variances

Interested in variances along the critical path

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Example

45.52645.1745.543

22.1745.5

7

33

4350)(2

ZD

DZ

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Toward Realistic Time Estimates

Calculations are based on 1% chance of beating estimates

Calculations can also be based on 5% or 10% Changing the percentage requires changing the

formulae for variance When using 5%, the divisor changes to 3.29 When using 10%, the divisor changes to 2.56