AMERICAN SPORTS BUILDERS ASSOCIATION

CRITICAL PATH METHODSCHEDULING FOR SUCCESS

December 6-8, 2008

New Orleans, Louisiana

Presented By: Bill Pronevitch

SCHEDULING- Is It Necessary?

• Effective Project Management involves coordinating activities such as:– Planning– Organizing– Controlling Time (scheduling)– Cost

• The “Scheduling” process forces people to:– Quantify their effort in discrete terms– Place tasks in proper relationships

SCHEDULING- Methodologies

• Two of the most common methodologies:– Bar Charts– Critical Path

• ADM: Arrow Diagramming Method• PDM: Precedence Diagramming Method

• Both scheduling methods are widely used for:– Controlling – Making optimal use of project time

SCHEDULING- Bar Charts

• Bar Charts (also called “Gantt Charts”) are primarily for controlling Time elements:– Analyze/ specify the basic approach to be used– Segment the work into a reasonable number of

activities that can be scheduled– Estimate the time required to perform each activity

(i.e.- activity duration)– Place activities in “time-order” (logic)– Adjust the chart until the specified completion date, if

one exists, is satisfied.

SCHEDULING- Bar ChartA

B

C

D

E

F

0 1 2 3 4 5 6 7 8 9 10 11 12

Gantt Chart (Bar Chart) shows:

•All Activities and Status on a Single

Chart

SCHEDULING- Bar Charts

• Benefits:– Plan, Schedule, and Progress on a single chart– A simple, understandable way to schedule small

projects or undertakings

• Disadvantages:– Activity-limited, can’t handle complex projects– Doesn’t show logic ties (activity relationships)– Insufficient detail to enable timely detection of

schedule slippages on long duration activities

SCHEDULING: Critical Path

• The Critical Path Method (CPM) was designed for and is useful on projects where the duration of each activity can be with reasonable certainty

- it predicts project overall completion

- it identifies the (critical) activities that control the overall length of the project

• CPM is widely used in: process industries construction and plant outages/ shutdowns.

SCHEDULING: Critical Path

• Benefits:– Determines shortest project completion time– Identifies “critical” activities – that can not be

slipped or delayed (i.e.- “TOTAL FLOAT”)– Shows allowable slippage for “non-critical”

activities (i.e.- “FREE FLOAT”)

• Disadvantages:– Large number of activities required– Difficult to read, understand, and maintain.

SCHEDULING: CPM/ADM

• ADM (Arrow Diagramming Method):– Arrow (line): represents an Activity– Tail (of arrow): shows an Activity’s start– Head (of arrow): shows an Activity’s finish– Node (or event): shown at each end

• The “Activity Number” consists of Head and Tail numbers, commonly referred to as I-J nodes (i.e.- “I-J Method” of CPM)

SCHEDULING: CPM/ADM

ADM: Arrow Diagramming Method

1 2 4 5

3

Process Work

Order

Requisition

Material

Install

Pump

Assign

Crew

(Dummy Activity – shows relationship, zero duration)

SCHEDULING: CPM/ADM

• Benefits:– Allows use of “Dummy Activities” which:

• Have a “ZERO” time duration• Can be used to show additional relationships

• Disadvantages:– An Activity’s “Predecessor” must be complete

before the Activity can start!– Neither the Activity’s “arrow length” or “arrow

direction” have any meaning

SCHEDULING: CPM/PDM

• PDM (Precedence Diagramming Method):– Box/ Node: represents an Activity– Line/ Arrow: represents a Precedence – with time and

direction properties

• Precedence consist of two parts:– “Relationship”: a Predecessor or Successor– “Lag”: the (positive or negative) number of work

periods by which a specified Activity will be delayed (assumed to be “0” if not specified)

SCHEDULING: CPM/PDM

PDM: Precedence Diagramming Method

A C

DE

Process Work Order

B

Requisition Material

Install Pump

Assign Crew

Pump Installation Completed

SCHEDULING: CPM/PDM

• Types of Relationships, Lags (aa,n):– FS, 0: Finish-to-Start, With “0 units” of delay

– FF, 7: Finish-to-Finish, with “7 units” of delay

– SS, 5: Start-to-Start, with “5 units” of delay

– SF, 0: Start-to-Finish, with “0 units” of delay

SCHEDULING – PDM/ LOGIC

Relationships (Logic Ties, Lags

A

B

A B

A B

A

B

Start –to- Finish

Finish -to- Finish

Finish –to- Start

Start –to- Start

(FS,0)

(FF,5)

(SS,4) (SF,0)

SCHEDULING: CPM/PDM

• “6” Major Types of Constraints– Start On: a mandatory date– Start No Earlier Than*: can start “later”– Start No Later Than*: can start “earlier”– Finish On: a mandatory date– Finish No Earlier Than*: can finish “later” – Finish No Later Than*: can finish “earlier”* NOTE: Schedule logic drives “earlier” and

“later” start and finish dates

SCHEDULING- PDM/ OTHER

• Hammock Activity– Spans many activities to show an “overall”

performance period (i.e.- a summary activity)

• Logic Loop– One of the most common “scheduling errors”– Occurs when a set of activities precede each

other in a “circular” fashion, (a group of activities can never begin nor end)

– Must be eliminated prior to calculating the schedule (i.e.- running a time analysis)

SCHEDULING- Hammock

PDM: Hammock (Summary) Activity

A B C

E

D

SCHEDULING – PMD/LOOP

LOOP: No beginning or end (a circular path)

LOOP

A B C D

EF

SCHEDULING – PDM/ CALC’S

• Once a network has been created and the durations estimated for each activity, both the “Total Time” to reach project completion and each activity’s “individual” start and finish times, can be calculated– Manual computation is easy and logical (but

tedious & time-consuming on large projects)• Forward Pass: calculates early start/finish, (ES/EF)• Backward Pass: calculates late start/finish, (LS/LF)

SCHEDULING – CALC’S

• FORWARD PASS:– Calculates “Earliest Start” and “Earliest

Finish” times, observing the following rules:• Assign an “ES” time to the first activity• Other activities start as soon as their

“predecessor” relationships have been satisfied• Equations:

– ES = EF (Pred.) + 1 – EF = ES + Duration - 1

SCHEDULING – CALC’S

• BACKWARD PASS:– Calculates “Latest Start” and “Latest Finish”

times, observing the following rules:• Assign an “EF” time to the last activity.• All activities finish as soon as their “Successor”

relationships have been satisfied.• Equations:

– LF = LS (Succ.) – 1– LS = LF – Duration + 1

SCHEDULING – CALC’S

• PDM ACTIVITY NOTATION:– Activity Number: unique number to an activity– Duration: number of “work periods” assigned– ES & EF: calculated in Forward Pass– LS & LF: calculated in Backward Pass

ACTIVITY NUMBER

ES EF

LS LF

DURATION

1 A 5

3 5 7

 10

 

5    

 20

 

4  

   

 50

 

4  

   

 60

 

 5 

   

 40

 

 14 

   

30 

 

5 

 

   

Legend

Activity ID 

 ES

Duration 

 EF

 LS  LF

START

FINISH

FORWARD & BACKWARD PASS

 10

 

5    

 20

 

4  

   

 50

 

4  

   

 60

 

 5 

   

 40

 

 14 

   

30 

 

5 

 

   

Legend

Activity ID 

 ES

Duration 

 EF

 LS  LF

START

FINISH

FORWARD & BACKWARD PASS

1 5 6 19

6 9 10 13 20 24

5 924

Early Dates:

ESs = EFp + 1

EFs = ESs + Ds - 1

 10

5  

 20

4 

 50

 

4  

 

 60

 5   

 40

 14 

30 

 

5 

 

 

Legend

Activity ID 

 ES

Duration 

 EF

 LS  LF

START

FINISH

FORWARD & BACKWARD PASS

24

51 6 19

12 15 16 19 20 24

11 15Late Dates:

LFp = LSs -1

LSp = LFp – D +1

 10

 1

5  5

 

 20

 6

4 9 

 50

10 

4  13

 

 60

 20

 5 24

   

 40

 6

 14 19

30 

 5

5 

 9

 

Legend

Activity ID 

 ES

Duration 

 EF

 LS  LF

START

FINISH

FORWARD & BACKWARD PASS

2424

51 6 19

12 15 16 19 20 24

11 15Late Dates:

LFp = LSs -1

LSp = LFp – D +1

What is the Scheduling Process?

Report/ Status

Scheduling

Planning

IDENTIFY MILESTONES

• Project Start

• Project Phase Start and Finishes

• Equipment and/ or Long Lead Item Delivery

• Project Finish

DEVELOP ACTIVITY LIST(EXAMPLE: HOUSE CONSTURCTION)

• Select Lot

• Clear and Grub Lot

• Install Utilities

• Construct House

• Select Contractors

• Arrange Financing

• Close Financing

• Landscape

• Purchase Appliance and Lighting Fixtures

• Install Flooring

• Paint

ASSIGN DURATION TO ACTIVITES(EXAMPLE: HOUSE CONSTRUCTION)

• Select Lot 3 days• Clear and Grub Lot 10 days• Install Utilities 3 days• Construct House 60 days• Select Contractors 5 days• Arrange Financing 5 days• Close Financing 1 day• Landscape 5 days• Purchase Appliance/Lighting Fixtures 1 day• Install Flooring 5 days• Paint 5 days

SEQUENCE ACTIVITIES

ASK THREE QUESTIONS!

• What activity must come before this one?

• What activity must come after this one?

• What activities can I perform at the same time?

REVIEW AND FINALIZE

• Review Relationships

• Review and Finalize Durations

• Review Resource Usage

• Review and Finalize Project End Date– Does this achieve the desired date?– If it does not…. What is the plan NOW?!?

SCHEDULING- CONCLUSION

• Planning and scheduling functions are usually performed iteratively in order to provide for accomplishing all required tasks within the specified time frames

• Both Critical Path Methods (ADM & PDM) create networks showing activity durations and total time for project completion

• “Failing to Plan is Planning to Fail”, hence “Plan the Work, Work the Plan”