3.1 NETWORK

Roger D. H. Warburton

Determine Activity Dependencies & Critical Path

© Kanabar /Warburton, 2009

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Objectives2

Objectives Understand concepts associated with

Activity Sequencing Critical Path Schedule Development

KNOWLEDGE AREA: TIME MANAGEMENT

A subset of project management that includes the processes required to ensure timely completion of the project. It consist of activity definition, activity sequencing, activity duration estimating, schedule development, and schedule control.

PMBOK® Guide (PMI)

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WHERE ARE WE?

Monitor and Control

4

WE COMPLETED …

5

Collect Requirements Define Scope Create WBSScope

WBS “DECOMPOSITION”

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MakeInvitations

1.2

Design1.2.1

Print1.2.2

Mail1.2.3

MakeInvitations

1.2.2

Mail1.2.2.3

Print1.2.2.2 Layout

1.2.1.1Pre-Press

1.2.2

DEVELOPING THE PROJECT PLAN

AddSequence

&Time!

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THE PROJECT NETWORK

A flow chart that graphically depicts the sequence, interdependencies, and start and finish times of the project

Leads to a plan of activities that is the critical path through the network

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FROM WORK PACKAGE TO NETWORK

A

B D

C

FinishStart

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THE NETWORK

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1.2

Start

MakeInvitations

1.2

Design1.2.1

Print1.2.2

Mail1.2.3

THE “ARROW”

D cannot start until A, B, and C have been completed

A

C

B D

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CONSTRUCTING A PROJECT NETWORK

Terminology

Activity:

An element of the project that requires time

A

C

B D

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TERMINOLOGYPath:

A sequence of connected, dependent activities.

Parallel (Concurrent) Activities:

Activities that can occur at the same time. (If desired)

C

A B D13

EVENT

A point in time when an activity is started or completed.

It does not consume time.

Milestones are events14

BURST ACTIVITYAn activity that has more than one activity

immediately following it (more than one dependency arrow flowing from it).

B

D

A C

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MERGE ACTIVITYAn activity that has more than one activity

immediately following it (more than one dependency arrow flowing from it).

B

D

AC

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SIMPLE EXAMPLE WITH EVERYTHING

Activity Predecessor Time

A None 5

B A 15

C A 10

D B,C 30

B

DA

C

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NOTATIONEarliestStart

IDIdentification

EarliestFinish

Slack Description Slack

LatestStart

Duration LatestFinish

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SIMPLE EXAMPLE: 1) FORWARD PASS (EARLIEST)

A

5C

10

B

15 D

30

ES ID EF

SL Des SL

LS Dur LF

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SIMPLE EXAMPLE: 1) FORWARD PASS (EARLIEST)

0 A 5

55 C 15

10

5 B 20

15 20 D 50

30

ES ID EF

SL Des Cr

LS Dur LF

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SIMPLE EXAMPLE: 2) BACKWARD PASS (LATEST)

C

10 10 20

B

5 15 20 D

20 30 50

Delivery Date= 50

0 A 5

0 5 5

ES ID EF

SL Des SL

LS Dur LF

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SIMPLE EXAMPLE: 3) SLACK = LS - ES

0 A 5

0

0 5 5 5 C 15

5

10 10 20

5 B 20

0

5 15 20 20 D 50

0

20 30 50

= LF - EF

C can be delayed

by 5

Float

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SIMPLE EXAMPLE: 4) PATH OF LEAST SLACK (LS – ES)

0 A 5

-10

-10 5 -5 5 C 15

-5

0 10 10

5 B 20

-10

-5 15 10 20 D 50

-10

10 30 40

-5-(+5)= -10 10-(+20)= -1023

SIMPLE EXAMPLE: 5) CRITICAL PATH

0 A 5

0

0 5 5 5 C 15

5

10 10 20

5 B 20

0

5 15 20 20 D 50

0

20 30 50

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CRITICAL PATH

The critical path is the network path(s) that has (have) the least slack in common.

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CRITICAL PATH the longest path through the network that allows for the

completion of all activities

the shortest expected time in which the entire project can be completed. Delays on the critical path will delay completion of the entire project.

C

A B D

T=3

T=5

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CRITICAL PATH ~ 10% Assign best people to critical activities

Prioritize (and eliminate) critical activities

Risk assessment on critical activities

Visit people working on critical activities

Can I borrow Joe?

Overtime, technology

Schedule changes ±

Roll up non criticals C

A B D

T=3

T=5 27

SIMPLE EXAMPLE: 6) FREE SLACK

0 A 5

0

0 5 5

5 C1 10

5

10 5 15

5 B 20

0

5 15 2020 D 50

0

20 30 5010 C2 15

5

15 5 20

Difference between EF and ES that follows it

05

Useful!

EF – ES

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BASIC NETWORK RULESNetworks typically flow from left to right.An activity cannot begin until all of its

predecessor activities are complete.Arrows indicate precedence and flow and can

cross over each other.Identify each activity with a unique number;

this number must be greater than its predecessors.

Looping is not allowed.Conditional statements are not allowed.Use common start and stop nodes.

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NETWORK COMPUTATION PROCESS

Forward Pass—Earliest Times

How soon can the activity start?Earliest start—ES

How soon can the activity finish?Earliest finish—EF

How soon can the project finish?Expected time—ET

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NETWORK COMPUTATION PROCESS

Backward Pass—Latest Times

How late can the activity start?Latest start—LS

How late can the activity finish?Latest finish—LF

Which activities represent the critical path?

How long can it be delayed?Slack or float—SL 31

FORWARD PASS COMPUTATION

Add activity times along each path in the network (ES + Duration = EF).

Carry the early finish (EF) to the next activity where it becomes its early start (ES) unless…

The next succeeding activity is a merge activity, in which case the largest EF of all preceding activities is selected.

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BACKWARD PASS COMPUTATION

Subtract activity times along each path in the network (LF - Duration = LS).

Carry the late start (LS) to the next activity where it becomes its late finish (LF) unless

The next succeeding activity is a burst activity, in which case the smallest LF of all preceding activities is selected.

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DETERMINING SLACK (OR FLOAT)

Slack (or Float) The amount of time an activity can be delayed after

the start of a longer parallel activity or activities. Total slack

The amount of time an activity can be delayed without delaying the entire project.

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ILLOGICAL LOOP

A

C

B

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ITERATION LOOP

Write CH 1

Edit CH 1??

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ARROWS MAY CROSS

A

C

B

D37

PRACTICAL CONSIDERATIONS

Network Logic ErrorsActivity NumberingUse of Computers to Develop

NetworksCalendar DatesMultiple Starts and Multiple

Projects38

EXAMPLE OF LADDERING

Dig Hole

Lay Pipe

Fill Hole

Dig 1/3 Hole Lay 1/3 Pipe Fill 1/3 Hole

Dig 2nd/3 Hole

Lay 2nd/3 Pipe

Dig 3rd/3 Hole 39

EXTENDED NETWORK TECHNIQUES:

1) LADDERING100% Complete too restrictiveOverlap & long durationActivities are broken into

segments so the following activity can begin sooner and not delay the work

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EXTENDED NETWORK TECHNIQUES:

2) LAGS

The minimum amount of time a dependent activity must be delayed to begin or end. Lengthy activities are broken

down to reduce the delay in the start of successor activities.

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USE OF LAGS

Finish-to-Start Lag

Typical: e.g., Ordering Materials

• Order Activity is 1 day• Material takes 5 days to arrive• Charge for 1 day

Order Assemble5 Days

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USE OF LAGSStart-to-Start Relationship

Assemble cannot begin until 5 days after Order begins

You can begin Assembly after a portion of Ordering

e.g., pipe laying, partial design

Order

Assemble5 Days

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USE OF LAGS

Finish-to-Finish Relationship

The finish of Assemble depends on the finish of the Order.

Assemble cannot finish any earlier than 5 days after Ordering is complete

Order

Assemble

5 Days

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USE OF LAGS

Start-to-Finish Relationship

Assemble cannot end until 5 days after Ordering has started.

(Because information to Assemble is available after the first 5 days of Ordering.)

Order

Assemble

5 Days

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USE OF LAGS

Can be used in Combinations!

Assemble cannot begin until 5 days after Ordering has started

andOrdering must be finished 3 days before Assemble can be finished.

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3) HAMMOCK ACTIVITIES

An activity that spans over a segment of a project.

Duration is determined after the network plan is drawn

Used to aggregate sections of the project

Facilitates getting the right amount of detail for specific sections of a project.

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HAMMOCK ACTIVITY EXAMPLE

Consulting, Machine Rental, etc.

Dig

Hole

Lay

Pipe

Patch

Pipe

Fill

Hole

RentBackhoe

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CONSTRUCTING A PROJECT NETWORK

Two ApproachesActivity-on-Node (AON)

Uses a node to depict an activity.

Activity-on-Arrow (AOA)Uses an arrow to depict an activity. 49

AOA EXAMPLE

Activity Predecessor Time

A None 5

B A 15

C A 10

D B,C 30

B

DA

C3

41 2A C D 5

B

A is 1-2C is 2-4D is 4-5

B is 3-450

AOA EXAMPLE

Activity Predecessor Time

A None 5

B A 15

C A 10

D B,C 30

B

DA

C3

41 2A C D 5

B

A is 1-2C is 2-4D is 4-5

DummyActivity

B is 3-42-3 is dummy, zero time

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AOA

Know advantages & Disadvantages

Not expect you to do AOA network

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AON & AOAAON AOA

+ No Dummy Activities + Paths simplified

+ Easier to draw for simple networks

+ Easier to draw for complex networks

+ Easily understood by managers

+ Key events easily flagged

− Hard to understand for complex networks

− Dummy activities− Emphasizes events, not activities

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SUMMARY TIME MANAGEMENT (PMBOK 4TH EDITION - 2008)

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Define Activities Sequence Activities

Estimate Activity Resources

Estimate Activity Durations

Develop Schedule

Time

The following are the Time Management Planning Processes

WORKSHOP

Estimate duration for activities Network and Schedule: Generate a MS

Project Schedule for the case study

ADDITIONAL READING

Good overview of Slack is at: http://office.microsoft.com/en-us/project/HA102118001033.aspx

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