Project Management OPER 576

Project Networks

Greg Magnan, Ph.D.

April 29, 2004

Project Life Cycle Stages

Definition Planning Execution/Impl./Control Closeout

Leve

l of E

ffort

Selection Charter Goals Specs Tasks Responsi

bilities

Estimates Schedules Sequencing Budgets Resources Risks Staffing

Status Reports Changes Quality Forecasts

Training Transfer

Documents Release

Resources Lessons

Learned

II. Project Planning7. Sequence Deliverables

• To help schedule work efficiently

• Consider all WBS elements

• Estimate calendar duration for each

• List precedence for each task

• May construct network diagram

• CRITICAL PATH: longest path through the network showing minimum time needed

• Delays to elements on the critical path delay the entire project!

• Mascitelli: Critical Core

Activity Time Estimates

• PERT-based• Assumptions:

– “normal” operations– independent estimates for activities

• Optimistic / Most-likely / Pessimistic• Formula

(O + 4M + P)/6

• Example(10 + 4*15 + 26)/6 = 16

Project Networks• Developed from WBS

– WBS must be deliverables-oriented!– Activity Labeling: use WBS outline as basis

• Used for Planning, scheduling, controlling• Activities, sequences, precedence rel’ps

• Critical Path / “Crashing” network

• Basis for Resource Scheduling

• Communication to stakeholders

• Estimate of project duration

EarlyStart

Duration

EarlyFinish

LateStart

SlackLate

Finish

Task Name

EarlyStart

Duration

EarlyFinish

LateStart

SlackLate

Finish

Task Name

EarlyStart

Duration

EarlyFinish

LateStart

SlackLate

Finish

Task Name

EarlyStart

Duration

EarlyFinish

LateStart

SlackLate

Finish

Task Name

EarlyStart

Duration

EarlyFinish

LateStart

SlackLate

Finish

Task Name

EarlyStart

Duration

EarlyFinish

LateStart

SlackLate

Finish

Task Name

EarlyStart

Duration

EarlyFinish

LateStart

SlackLate

Finish

Task Name

Network Terms• Activity

– An element in the project that consumes time, but doesn’t necessarily require resources (e.g., approvals, contract signing)

• “Events” do not consume time– Can include one or more Work Packages

• Verb/noun format

• Critical path– Path: a sequence of connected, dependent activities– CP: Longest path through the network

• Activity-on-Node (AON) vs. Activity-on-Arc (AOA)– AON is most commonly used (software packages)– Nodes reflect activities

AON Network Development Rules• Arrows indicate precedence and flow

– Flow from left to right– Precedence determined after WBS complete

• Predecessor and Successor activities

– Preceding activities must be complete before beginning successor activities

• Activities need labels– Larger numbers than preceding activities

• No Looping!– No conditional (if/then) statements

• Single Start and End nodes

Project Scheduling: Node Elements

Early Start Duration Early Finish

Late Start Slack Late Finish

Task Name

PERT Diagram(Activity on Node)

EarlyStart

Duration

EarlyFinish

LateStart

SlackLate

Finish

Task Name

EarlyStart

Duration

EarlyFinish

LateStart

SlackLate

Finish

Task Name

EarlyStart

Duration

EarlyFinish

LateStart

SlackLate

Finish

Task Name

EarlyStart

Duration

EarlyFinish

LateStart

SlackLate

Finish

Task Name

EarlyStart

Duration

EarlyFinish

LateStart

SlackLate

Finish

Task Name

EarlyStart

Duration

EarlyFinish

LateStart

SlackLate

Finish

Task Name

EarlyStart

Duration

EarlyFinish

LateStart

SlackLate

Finish

Task Name

Sample Problem

Activity Duration PredecessorA 5 noneB 10 noneC 15 AD 10 AE 5 BF 20 CG 20 EH 5 D, F, GI 15 H

Forward & Backward Pass• Determine:

– Early Start (ES) and Early Finish (EF)

– Late Start (LS) and Late Finish (LF)…and then Slack

• Forward Pass (EF and ES)– For each path in the network, add activity times (duration)

to each ES to get EF (ES + Dur = EF)

– EF of preceding activity becomes ES of successor, unless• Succeeding activity is a merge activity (>1 predecessor)

• Then select LARGEST EF time from all predecessor EF times to become ES for successor activity

Forward & Backward Pass• Backward Pass (LF and LS)

– Must have already completed Forward Pass

– Start with the latest EF of last activity in the network

– For each path in the network, subtract activity times (duration) from each LF to get LS (LF - Dur = LS)

– LS of successor activity becomes LF of preceding, unless

• The next preceding activity is a burst activity (>1 successor)

• Then select SMALLEST LS time from all immediate successor activities to determine LF time

Conclusion…

• Projects are everywhere

• Can be actively managed

• Science AND art