Week 7-Project Scheduling

9-1

Project Scheduling: Networks, Duration

Estimation,

and Critical Path

Project Scheduling

� Project scheduling requires us to follow some carefully laid-out steps, in order, for the schedule to take shape.

� Project planning, as it relates to the scheduling process, has been defined by the PMBoK as:

The identification of the project objectives and the ordered activity necessary to complete the project including the identification of resource types and quantities required to carry out each activity or task.

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Purposes of Project Scheduling

1. Shows the relationship of each activity to others and to the whole project

2. Identifies the precedence relationships among activities

3. Encourages the setting of realistic time and cost estimates for each activity

4. Helps make better use of people, money, and material resources by identifying critical bottlenecks in the project

Project Management Techniques

� Gantt chart� Critical Path Method (CPM)� Program Evaluation and

Review Technique (PERT)

A Simple Gantt Chart

TimeJ F M A M J J A S

Design

Prototype

Test

Revise

Production

Passengers

Baggage

Fueling

Cargo and mail

Galley servicing

Lavatory servicing

Drinking water

Cabin cleaning

Cargo and mail

Flight services

Operating crew

BaggagePassengers

DeplaningBaggage claim

Container offloadPumping

Engine injection waterContainer offloadMain cabin doorAft cabin door

Aft, center, forwardLoading

First-class sectionEconomy section

Container/bulk loadingGalley/cabin check

Receive passengersAircraft check

LoadingBoarding

0 10 20 30 40Time, Minutes

Service For A Delta Jet

Figure 3.4

Six Steps PERT & CPM

1. Define the project and prepare the work breakdown structure

2. Develop relationships among the activities -decide which activities must precede and which must follow others

3. Draw the network connecting all of the activities

Six Steps PERT & CPM

4. Assign time and/or cost estimates to each activity

5. Compute the longest time path through the network –this is called the critical path

6. Use the network to help plan, schedule, monitor, and control the project

Project Scheduling Terms�Successors

�Predecessors

�Network diagram

�Serial activities

�Concurrent activities

ED

C

B

A F

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Project Scheduling Terms

ED

C

B

A F

• Merge activities

• Burst activities

• Node

• Path

• Critical Path

09-010

FIGURE 9.2 Alternative Activity Networks for Term Paper Assignment

Network Diagrams

Copyright © 2013 Pearson Education09-011

AOA Versus AON

The same mini-project is shown with activities on arc…

C

ED

B F

E

C

DB F

…and activities on node.

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Node Labels

Early Start

Activity FloatActivity Descriptor

Late Start

ID Number

Activity Duration Late Finish

Early Finish

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FIGURE 9.5

Serial Activities

Serial activities are those that flow from one to the next, in sequence.

09-14 Copyright © 2013 Pearson Education

FIGURE 9.6

Activities Linked in Parallel

(Concurrent)


When the nature of the work allows for more than one activityto be accomplished at the same time, these activities are called

concurrent and parallel project paths are constructed through thenetwork.

FIGURE 9.7

Merge Activity


FIGURE 9.8

Burst Activity


AON Example

Activity DescriptionImmediate

Predecessors

A Build internal components —

B Modify roof and floor —

C Construct collection stack A

D Pour concrete and install frame A, B

E Build high-temperature burner C

F Install pollution control system C

G Install air pollution device D, E

H Inspect and test F, G

Activities and Predecessors

Table 3.1

AON Network

G

E

F

H

CA

Start

DB

Arrows Show Precedence Relationships

Figure 3.8

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TRY THE FOLLOWING:Construct a network activity diagram based on the following information:

Activity Preceding activitiesA -B -C AD B, CE BF C, DG EH FI G, H

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A

B

C

D

E

F

G

H

I

Node Labels

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Early Start

Activity Float Activity Descriptor

Late Start

ID Number

Activity Duration

Late Finish

Early Finish

Duration Estimation Methods

� Past experience

� Expert opinion

� Mathematical derivation – Beta distribution

� Most likely (m)

� Most pessimistic (b)

� Most optimistic (a)

4 = TE

6

a m bActivity Duration

+ +=

9-23

22 =

6

b aActivity Variance σ − =

Activity Duration and Variance

09-24

Name: Project Delta

Durations are listed in weeks

Activity Description Optimistic Likely Pessimistic

A Contract signing 3 4 11

B Questionnaire design 2 5 8

C Target market ID 3 6 9

D Survey sample 8 12 20

E Develop presentation 3 5 12

F Analyze results 2 4 7

G Demographic analysis 6 9 14

H Presentation to client 1 2 4

Copyright © 2013 Pearson Education

Table 9.2

Sketch the network described in the table.Determine the expected duration and variance of each

activity.

Task Predecessor a m b

Z -- 7 8 15

Y Z 13 16 19

X Z 14 18 22

W Y, X 12 14 16

V W 1 4 13

T W 6 10 14

S T, V 11 14 19

9-25

Constructing the Critical Path

� Forward pass – an additive move through the network from start to finish

� Backward pass – a subtractive move through the network from finish to start

� Critical path – the longest path from end to end which determines the shortest project length

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Rules for Forward/Backward

PassForward Pass Rules (ES & EF)

� ES + Duration = EF

� EF of predecessor = ES of successor

� Largest preceding EF at a merge point becomes ES for successor

Backward Pass Rules (LS & LF)� LF – Duration = LS

� LS of successor = LF of predecessor

� Smallest succeeding LS at a burst point becomes LF for predecessor

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Project Delta Information

09-28

Project Delta

Activity Description Predecessors Estimated Duration

A Contract signing None 5

B Questionnaire design A 5

C Target market ID A 6

D Survey sample B, C 13

E Develop presentation B 6

F Analyze results D 4

G Demographic analysis C 9

Copyright © 2013 Pearson Education

Table 9.4

H Presentation to client E, F, G 2

FIGURE 9.16 Partial Project Activity Network with Task Durations


FIGURE 9.19 Activity Network with Backward Pass


FIGURE 9.20 Project Network with Activity Slack and Critical PathNote: Critical path is indicated with bold arrows.


Sketch the network described in the table.

Determine the ES, LS, EF, LF, and slack of each activity

Task Predecessor Time

A -- 4

B A 9

C A 11

D B 5

E B 3

F C 7

G D, F 3

H E, G 2

K H 1

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Laddering Activities

9-34

•It may be possible to begin a portion of one activity while work continues on other elements of the task, particularly in lengthy or complex projects.•Create a visual basic code composed of several subroutines to cover the systems of multiple departments.•Under sever time pressure to use our resources efficiently, however, we might want to find a method for streamlining, or making the development sequence more efficient.

Laddering Activities

Project ABC can be completed more efficiently if subtasks are used

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A(3) B(6) C(9) ABC=18 days

Laddered ABC=12 days

A1(1) A2(1) A3(1)

B1(2) B2(2) B3(2)

C1(3) C2(3) C3(3)

Hammock Activities

� Summaries for some subsets of activities identified in the overall project network.

� Hangs below the network path for consultant tasks and serves as an aggregation of task durations for the activities it “ROLLS UP”

� Duration – first identifying all tasks to be included and then subtracting the ES or the first task from the EF from the EF of the latest successor.

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Hammock Activities

Used as summaries for subsets of activities

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0 A 5

0 5 5

5 B 15

5 10 15

15 C 18

15 3 18

0 Hammock 18

0 18 18

Useful with a complex project or one that has

a shared budget

Reducing the Critical Path

� Eliminate tasks on the CP

� Convert serial paths to parallel when possible

� Overlap sequential tasks

� Shorten the duration on critical path tasks

� Shorten

� early tasks

� longest tasks

� easiest tasks

� tasks that cost the least to speed up

9-38

Exercise:Calculate the ES, LS, EF, LF and slack time in a table format. Find the critical path.

Week 7-Project Scheduling

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