Slides by: Ms. Shree Jaswalssjaswal.com/wp-content/uploads/2018/08/SPM_Chp4_part1.pdfMost software packages create AOA n/w’s that look similar to Gantt charts. In particular it is

Slides by: Ms. Shree Jaswal

Introduction

developing the project schedule

Scheduling Charts

logic diagrams and network (AOA,AON)

critical path

calendar scheduling and time based network

management schedule reserve

PDM network,

PERT

CPM

Resource loading, resource leveling

allocating scarce resources to projects and several projects

Goldratt’s critical chain.

Chapter 4 Slides by: Ms. Shree Jaswal 2

Textbook:

* Chp 7: The Project's Schedule and budget

Reference Books:

#1 Chp 7: Network Scheduling and PDM

#1 Chp 8:PERT, CPM, Resource Allocation and GERT

#1 Chp 9: Cost estimating and budgeting

#1 Chp 10:Managing risks in projects

#2 Chp 8:Project Activity Scheduling

Note:* Textbook: "Information Technology Project Management" Jack T.

Marchewka

#1 Reference book: "Project Management for business and Technology"

John M. Nicholas

#2 Reference book: "Project Management" Jack R. Meredith



Activity definition

Activity sequencing

Activity duration estimation

Schedule development

Schedule control


Project Management Tools

Gantt Charts

Project Network Diagrams

Activity on the Node (AON), Activity on arrow (AOA)

Critical Path Analysis

Pert

Precedence Diagramming Method (PDM)


Simplest and most commonly used scheduling

technique

The chart consists of horizontal scale divided into

time units-days, weeks or months and vertical

scale showing project work elements.


Advantages:

Gives a clear pictorial model of the project.

Simplicity for the planner and the user.

Easy to construct & understand.

Is a means for assessing the status of individual work elements and the project as a whole.

It can be used as Expense Charts

1.for labor planning

2.resource allocation

3.budgeting






Drawbacks:

It does not explicitly show interrelationships

among work elements.

Gantt charts are often maintained manually. This

is easy task in small projects, but is burdensome

and a disadvantage in large projects; it causes

apathy and results in charts becoming outdated.


Activity Start time Duration

A 0 5

B 6 3

C 7 4

D 8 5

14Chapter 4 Slides by: Ms. Shree Jaswal

0 6 12 18 24 30

Gantt charts

Time

Activitie

s


Suppose C & D must start only after activity B is

completed.


0 6 12 18 24 30

Gantt charts

Time

Activitie

s


Gantt charts don’t explicitly show task

relationships

don’t show impact of delays or shifting

resources well

network models clearly show

interdependencies


network of relationships

elements & relationships (sequence)

this is ACTIVITY-ON-NODE

can have ACTIVITY-ON-ARC

research

what’s

been done

research

what needs

doing pick

final

topicinternet

research

write print


Activity on node diagrams

A,6 B,9


Activity on arc or arrow

21 3


Activity Duration Immediate Predecessor

A 6 _

B 9 A

C 8 A

D 4 B,C

E 6 B,C

Duration is given in weeks


AON diagram corresponding to data in prev table

Critical path A-B-E:21 weeks

Start A,6

B,9 D,4

C,8 E,6

Finish


Activity on arc or arrow

Same example on AON network

1 2

A,12


Activity Immediate Predecessors Duration

A _ 6

B A 9

C A 8

D B,C 4

E B 6

F D,E 6

Duration is in days


1 2



A _ 6

B A 9

C A 8

D B,C 4

E B 6

F D,E 6

Duration is in days


1 2

4

3



A _ 6

B A 9

C A 8

D B,C 4

E B 6

F D,E 6

Duration is in days


1 2

4

3

55 6



A _ 6

B A 9

C A 8

D B,C 4

E B 6

F D,E 6

Duration is in days


1 2

4

3

5 6

7



A _ 6

B A 9

C A 8

D B,C 4

E B 6

F D,E 6

Duration is in days


3-5, 4-5, 7-8,6-8 are dummy activities

1 2

4

3

5 6

7

8 9


Dummy activities are used in AOA diagrams in case a node has more than one immediate predecessor.

In previous example:Activity Immediate Predecessors Duration

D B,C 4

F D,E 6

To represent activities D & F we use dummy activities


ACTIVITY PREDECESSOR IMMEDIATE PRED: REDUNDANT PRED:

A --

B A A

C A A

D A,B,C B,C A

E A,B,C,D D A,B,C

F A,B,C B,C A

REDUNDANT ACTIVITY


It is only essential to know the immediate

predecessor of a node while constructing a

network.

All the predecessors except the immediate

predecessors of a node are redundant

predecessors( activities).


AON n/ws

There are no dummy activities

They are simpler

They are easier to construct.


AOA n/w’s

AOA method used just as often, probably because it was developed first and is better suited for PERT procedures

The PERT model places emphasis on events and in the AOA method events are specifically designated by nodes.

AOA diagrams use line segments to represent flow of work and time, it is easy to construct schedules that are similar in appearance to Gantt charts but incorporate advantage of networks


Most software packages create AOA n/w’s

that look similar to Gantt charts.

In particular it is best to select one form of

technique., AON or AOA, and stick to it.


The longest path from the origin node to the terminal

node

Gives the expected project duration (Te)

One project can have more than one CP

Shortening activities on CP (critical activities) will

help reduce the project duration

Shortening activities NOT on CP has no effect on

project duration

Delay in any activities on CP will result in delay of

project completion


Start A,6

B,9 D,4

C,8 E,6

Finish

Critical path A-B-E:21 weeks

Activity,

duratio

n

predece

ssor

A,6 -

B,9 A

C,8 A

D,4 B,C

E,6 B,C


Specifies when at the earliest the activities can be

performed.

ES & EF are computed by taking a FORWARD pass

through the network

When an activity has several predecessors, its ES is

the MAXIMUM of all EF of predecessors


Latest allowable times that the activity can be started

and finished without delaying the completion of the

project.

LS & LF are computed by taking a REVERSE pass

through the network. LS for the last activity (Ts) is

taken same as the EF for that activity (Te); larger value

can be selected if project does not have to be

completed by EF.

When an activity with multiple paths leading back,

backward path with MINIMUM of all LS is selected.


Eg:

activity duration__predecessor

A requirements analysis 3 weeks -

B programming 7 weeks A

C get hardware 1 week A

D train users 3 weeks B, C


Critical path is: A-B-D 13 weeks

1 2

3

4

5 6


Total slack= LS-ES or LF-EF

Total slack of all activities along critical path

is zero.

Hence delaying any of these activities will

delay the project.


Free Slack= ES( earliest successor)- EF

In the eg, activity C has a free slack of 6

weeks( 10-4=6)

Free slack indicated the amount by which

activity can be delayed without affecting the

start of its successor activity.


can have more than one critical path

activity duration predecessor

A requirements analysis 3 weeks -

B programming 7 weeks A

C get hardware 7 weeks A

D train users 3 weeks B, C

critical paths A-B-D

A-C-D

both with duration of 13 weeks


After a project network has been created

and finalized the resulting schedule times

should be converted into a calendar schedule

plan

Calendar schedule plan expresses the

schedule in terms of calendar dates


To complete the calendar schedule, the

network is converted into a time-based

network

Time based n/w’s have advantages of both

Gantt charts and networks because they

show the calendar schedules as well as

relationships among activities.





The Te first computed from the n/w is usually not the duration specified as the contractual completion time.

A Management schedule reserve is established by setting the required target time Ts at some amount greater than the time of the final schedule event Te.


The schedule reserve and a management

budget reserve comprise a “safety buffer” that

the project manager can use to overcome

problems or delays that threaten project

performance


Need for PDM: “Predecessor - Sucessor” type of networks

assume a “strict” sequential relationship between activities

They do not provide for tasks that can be started when their predecessors are only “partially” complete

PDM allows multiple relationships between activities Finish-to-Start (FS)

Start-to-Start (SS)

Start-to-Finish (SF)

Finish-to-Finish (FF)


Finish-to-Start (FS)

The start of the Activity B can occur n days, at the earliest after the finish of Activity A

Start-to-Start (SS)

The start of Activity B can occur n days, at the earliest after the start of Activity A


Start-to-Finish (SF)

The finish of Activity B must occur n days,

at the latest after the start of Activity A

Finish-to-Finish (FF)

The finish of Activity B will occur in n

days, at the latest after Activity A finishes


PDM: RelationshipsA 15

PlasterWall

B 10Tear-down scaffolding

FS=5

A

FS=5

B

A 15Furniture move in

B 10Peoplemove in

SS=5

A

SS=5

B

A 15Test

new system

B 10Phase outold system

SF=20

A

SF=20

B

A 15Lay

asphalt

B 10Paint

parking linesFF=5

A

FF=5

B

60Chapter 4 Slides by: Ms.

Shree Jaswal

The two most commonly used methods for project planning and scheduling are:

Program Evaluation and Review Technique (PERT)

Critical Path method (CPM)


Program Evaluation & Review Technique (PERT)

The Framework for PERT and CPM

There are six steps which are common to both

1. Define the Project and all of it’s significant activities or tasks.

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


3. Draw the "Network" connecting all the activities. Each Activity should have unique event numbers. Dummy arrows are used where required to avoid giving the same numbering to two activities

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.


PERT was developed for application in projects where there is uncertainty associated with the duration and nature of activities.


reflects PROBABILISTIC nature of durations

assumes BETA distribution

same as CPM except THREE duration estimates

optimistic

most likely

pessimistic


Three time estimates :

The Optimistic (a) The minimum time in which the activity can be

completed

The Most Likely (m) Completion time having the highest probability

(normal time to complete the job)

The Pessimistic (b)

The longest time an activity could take to complete



a = optimistic duration estimatem = most likely duration estimateb = pessimistic duration estimate

Mean or expected time for completion of an activity , te is given byte = (a + 4m + b)/6

Variance, V is given byV = sqr((b-a)/6)


The expected time Te , represents the point on distribution where there is a 50-50 chance that the activity will be completed earlier or later than it.

a=3,b=5,c=13

Te= (3+4(5)+13)/6= 6 days

Variance is the measure of variability in the activity completion time:

V=sqr((13-3)/6)=sqr(1.67)= 2.78


The larger V, the less reliable Te, and the higher the likelihood that the activity will be completed much earlier or much later than Te.

More dispersed the distribution and greater the chance that the actual time will be significantly different from the expected time Te


Probability of finishing by a target completion

date

The expected duration of a project - Te, is the

sum of expected activity times along the

critical path.

Te = ∑ te

The variation in the project duration

distribution is computed as the sum of the

variances of the activity durations along the

critical path

Vp = ∑ V



Now, although the project is estimated to be completed

within 29 weeks (Te=29) our Project Director would

like to know what is the probability that the project

might be completed within 27 weeks (i.e.Ts=27 or Due

Date or D=27).

For this calculation, we use the formula for calculating

Z, the number of standard deviations that D is away

from Te.

Z =(Ts-Te)/ √ Vp


Thus, Z=(27-29)/ √ 6 = -0.82

After referring to table for Z values for normal

distribution,

X1=-0.8,X2=-1.0,Y1=0.212,Y2=0.159

Now, using the formula,

Y=Y1+[(Y1-Y2)/X1-X2)]*(X-X1), we get

Y=0.2067=0.21(approx)

Therefore, probability is 21% to finish project

in 27 days



For above example to find out what is the date

when 95% of project will have been

completed…..

Again using the table and interpolating,

probability of 0.95 has Z value=1.645

Thus,1.645=(Ts-29)/ √ 6

So, Ts=33.03 days (highly likely)


Putting too much emphasis on the critical

path can lead managers to ignore other paths

that are near-critical or have large variances,

and which themselves could easily become

critical


Monte Carlo simulation is a procedure that takes into account the effects of near critical paths becoming critical.


Need to have considerable amount of

historical data to make time estimates

PERT gives overly optimistic results.

Beta distribution gives large errors in

estimating Te.

Most of the errors in Te come from faulty

time estimates not Beta distribution.


Although PERT and CPM employ networks and use the concept of critical path, the methods have two points of divergence.

CPM is a deterministic approach.CPM includes a mathematical procedure

for estimating the trade-off between project duration and cost.

CPM features analysis of reallocation of resources from one job to another to achieve the greatest reduction in project duration for the least cost.



BASIS FOR

COMPARISONPERT CPM

Meaning PERT is a project

management

technique, used to

manage uncertain

activities of a

project.

CPM is a statistical

technique of project

management that

manages well defined

activities of a

project.

What is it? A technique of

planning and control

of time.

A method to control

cost and time.

Orientation Event-oriented Activity-oriented

Evolution Evolved as Research

& Development

project

Evolved as

Construction project


BASIS FOR

COMPARISONPERT CPM

Model Probabilistic Model Deterministic Model

Focuses on Time Time-cost trade-off

Estimates Three time estimates One time estimate

Appropriate for High precision time

estimate

Reasonable time

estimate

Critical and Non-

critical activities

No differentiation Differentiated

Suitable for Research and

Development Project

Non-research

projects like civil

construction, ship

building etc.

Crashing concept Not Applicable Applicable

Documents

Slides by: Ms. Shree Jaswalssjaswal.com/wp-content/uploads/2018/08/SPM_Chp4_part1.pdfMost software packages create AOA n/w’s that look similar to Gantt charts. In particular it is