Project Management: A Managerial Approach Chapter 8 – Scheduling

Overview WBS to Schedule Process PERT Schedule Types CPM

Scheduling Def.: A schedule is the conversion of a project action plan into an operating timetable Is the basis for monitoring and controlling project activity Taken together with the plan and budget, it is probably the major tool for the management of projects

Scheduling In a project environment, the scheduling function is more important than it would be in an ongoing operation Projects lack the continuity of day-to-day operations (routine) and often present much more complex problems of coordination

Scheduling The basic approach of all scheduling techniques is to form a network of activity and event relationships This network should graphically portray the sequential relations between the tasks in a project Tasks that must precede or follow other tasks are then clearly identified, in time as well as function

Scheduling Networks Such networks are a powerful tool for planning and controlling a project and have the following benefits: consistent framework for planning, scheduling, monitoring, and controlling the project illustrates the interdependence of all tasks, work packages, and work elements denotes the times when specific resources are or must be available for work on a given task

Scheduling Network benefits (cont.): Facilitates communications that take place between departments and functions involved in the project. determines an expected project completion date identifies so-called critical activities that, if delayed, will delay the project completion time identifies activities with slack that can be delayed for specific periods without penalty

Scheduling Network benefits (cont.): determines the dates on which tasks may be started - or must be started if the project is to stay on schedule illustrates which tasks must be coordinated to avoid resource timing conflicts illustrates which tasks may run, or must be run, in parallel to achieve the predetermined project completion date relieves some interpersonal conflict by clearly showing task dependencies

Gantt Charts Advantages: easily understood / constructed / maintained Great visual tool to know project status (early, on time, late) requires frequent updating, but are easy to maintain Most popular way of providing a clear picture of the current state of a project (client, management, etc.)

Gantt Charts Disadvantages: superficial Hard to see activity precedents at times.

Gantt Charts Show planned and actual progress for a number of tasks displayed against a horizontal time scale Effective and easy-to-read method of indicating the actual current status for each set of tasks compared to planned progress for each item Helpful in expediting, sequencing, and reallocating resources among tasks Usually do not show technical dependencies

Simple Schedule – Gantt Chart

Network Techniques: PERT and CPM With the exception of Gantt charts, most common approach to scheduling is the use of network techniques such as PERT and CPM The Program Evaluation and Review Technique (PERT) was developed by the U.S. Navy in 1958 The Critical Path Method (CPM) was developed by DuPont, Inc during the same time period.

Network Techniques: PERT and CPM Advantages Can visualize task relationships. Facilitates CP (Critical Path) Calculation Can see impact of decisions on downstream activities. Disadvantages May be complex, not easy to understand at a glance.

New Names for PERT and CPM Most everyone knows techniques as PERT and CPM. In 2005, PMI decided to rename them. New names: ADM/PERT: Arrow Diagram Method PDM/CPM: Precedence Diagram Method.

Scheduling 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. An identifiable end state occurring at a particular time. Events use no resources. Network - The combination of all activities and events define the project and the activity precedence relationships

Scheduling Terminology Path - The series of connected activities (or intermediate events) between any two events in a network Critical - Activities, events, or paths which, if delayed, will delay the completion of the project. A project’s critical path is understood to mean that sequence of critical activities that connect the project’s start event to its finish event

Scheduling Terminology An activity can be in any of these conditions: It may have a successor(s) but no predecessor(s) - starts a network It may have a predecessor(s) but no successor(s) - ends a network It may have both predecessor(s) and successor(s) - in the middle of a network Interconnections from horizontal links in vertical WBS

Drawing Networks Activity-on-Arrow (AOA) networks use arrows to represent activities while nodes stand for events Activity-on-Node (AON) networks use nodes to represent activities with arrows to show precedence relationships The choice between AOA and AON representation is largely a matter of personal preference

Sample Input Information to a CPM Problem (Action Plan) Activity* A B C D E F Duration (weeks) 14 3 7 4 10 Predecessor Start A,B C,D * Activities could be Deliverables, Tasks, Subtasks or Operations.

(AON): Letters indicate activities, Arrows indicate relations A Sample Network (AON) Start A 14 C 3 E 4 F 10 B D 7 Finish Calculate: Project Duration Critical Path (CP) Activities on CP (AON): Letters indicate activities, Arrows indicate relations

The Critical Path (CP) A 14 C 3 Start E 4 F 10 B 3 D 7 Finish ES = 0 ES: Earliest (Possible) Starting Time EF: Earliest (Possible Finish Time

Determining Slack How much slack is there Where is it? How do you know? Why might you care?

Determining Slack Work Back . . . Critical Activity Start A 14 C 3 E 4 F 10 B D 7 Finish ES = 0 EF = 14 LS = 0 LF = 14 ES = 14 EF = 17 LS = 14 LF = 17 ES = 17 EF = 21 LS = 17 LF = 21 ES = 21 EF = 31 LS = 21 LF = 31 EF = 3 LS = 7 LF = 10 ES = 3 EF = 10 LS = 10 Work Back . . . Critical Activity LS: Latest Starting Time LF: Latest Finish Time

PERT

AOA (Activity on Arrow) Network Building Blocks 80 79 Install software Event Activity

AOA (Activity on Arrow) Network Building Blocks AON AOA

AOA (Activity on Arrow) Network Building Blocks AON AOA Activity on Node Activity on Arrow

AOA (Activity on Arrow) Network Building Blocks Any activity must have its source in one and only one node. If two activities occur between the same two nodes, insert a “dummy node” & activity w/duration 0.

AOA (Activity on Arrow) Network Building Blocks If c is not required to start e, then separate c by using another dummy node and arrow: a and b are required to start e, and a,b and c are required for d.

AOA (Activity on Arrow) Network Building Blocks - a precedes d; a and b precedes e; b and c precedes f; a does not precede f.

Gantt Chart

Gantt Chart

PERT

PERT Activity Calculation TE = a + 4m + b a = Most Optimistic (MO) 6 m = Most Likely (ML) b = Most Pessimistic (MP) t(e) = Activity Duration When a single estimate for activity time is not sufficient!

PERT Schedule Probability Z = T(S) – T(E) Z = Probability of SSD(T[E])2 Meeting Schedule T(S) = Scheduled Duration T(E) = Critical Path Duration Z is derived from a table of predetermined probabilities

Distribution of Possible Activity Times What is the probability of finishing the project (or an activity) in x days?

Probability Distribution Probability of finishing the project in 50 days? About 89% This is a tool to set your confidence in completing in X days.

Activity and Project Frequency Distributions m b TE (A) (B)

PERT Activity Times & Variances b t(e) 1-2 17 29 47 2-3 6 12 24 2-4 16 19 28 3-5 13 4-5 2 5 14 5-6 8

Variance of Activity Estimates b t(e) [(b-a)/6]2 Var 1-2 17 29 47 30 2-3 6 12 24 13 2-4 16 19 28 20 3-5 4-5 2 5 14 5-6 8

Possible Project Durations TE=64 TS=67

Z Table Z Value Probability -2.0 0.02 +2.0 0.98 -1.5 0.07 +1.5 0.93 -1.0 0.16 +1.0 0.84 -0.7 0.24 +0.7 0.76 -0.5 0.31 +0.5 0.69 -0.3 0.38 +0.3 0.62 -0.1 0.36 +0.1 0.54

Z-Table Expanded

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