Project Network Diagrams overview

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Project Network Diagrams (overview)

• Comm 589
• Mats Gerschman

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Learning objectives

• To understand what a Network diagram represents
  in project management
• To understand what is meant by predecessor and
  successor activities
• Understand how to calculate slack
• Understand how to find the critical path and why
  this is important

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Definition Project Network Diagram

• The activities and the activity durations to
• pictorially represent the sequences in
• which the project work can be done.

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Network representations of projects

• Diagrams that represent activities, events
  (milestones), precedence relations, and durations
• A network (or graph) consists of
• Nodes (points)
• Arcs (lines, links)
• Numbers associated with the nodes and/or arcs
• Two styles of project networks
• PERT
• CPM

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PERT and CPM

• PERT Program Evaluation and Review Technique
• Activity on arcs
• Nodes represent events (start, end of activities)
• May need dummy activities to represent some
  precedences
• CPM Critical Path Method
• Activity on nodes
• Arcs represent the precedences
• Extra nodes (activities) for milestones (incl.
  the start and end of whole project)
• Both represent the logical structure of the
  project
• In particular, line lengths do not represent time
  or durations

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CPM Network Diagram an example

• Setting up a new nursing home facility
• Define activities
• Activity A run pilot service in new facility
• Activity B build facility
• Activity C install equipment and furnishing
• Activity D recruit staff
• Activity E train staff
• Activity F pass safety inspection
• Identify precedences
• Activity A predecessors are C, E, F
• Activity B no predecessor
• Activity C predecessor is B
• Activity D no predecessor
• Activity E predecessor is D
• Activity F predecessor is B

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Precedence relations

• 3) Diagram the precedence requirements

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Project scheduling

• Gantt Chart
• A bar chart showing activity progress vs time
  used for both scheduling and control

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Critical path method (CPM)

• Main ideas
• Whole project should be completed ASAP (but while
  keeping an eye on costs)
• Ex) penalties for late completion
• For this, activities,
• that are unrelated by precedences, and do not
  share resources, may be undertaken simultaneously
• Identify critical activities, ie, those for which
  any delay will delay the whole project
• Allocate resources among activities to find the
  right time/cost tradeoffs.

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Critical path method cont.

• Schedule the start and end times of each
  activity, so as
• To secure the corresponding resources
• To be able to monitor that project is on track
• Schedule expenditures and resources

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Logical steps

• Forward pass for each activity, find its
• earliest start time ES
• earliest finish time EF
• Backward pass for each activity, find its
• latest finish time LF
• latest start time LS
• For each activity, find its slack time
• S LS ES
• Identify the critical activities, where S 0,
  and the critical path(s)

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Activity durations
C, 3
B, 24.3
A, 5.5
F,15.3
D,2.1
E,5
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Forward pass?determine the earliest project
completion time

• set time to start project, say 0
• determine the earliest start times ES
• an activity can start as soon as all its
  predecessors are completed, but no sooner
• and the earliest finish times
• EF ES activity duration

24.3, 27.3
0, 24.3
45.1
0
39.6, 45.1
24.3, 39.6
0,2.1
2.1, 7.1
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Backward pass?determine the latest start times

• set time to finish project,
• Normally, the earliest project completion time
  (found in the forward pass)
• determine the latest finish times LF
• an activity can finish before all its
  successors are started, but no later
• and the latest start times
• LS LF - activity duration

36.6, 39.6
0, 24.3
39.6, 45.1
24.3, 39.6
45.1
0
32.5, 34.6
34.6, 39.6
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Slack times S LS ES

• 4. Critical activities S 0
• and Critical path (or paths)

12.3
0
0
0
0
0
32.5
32.5
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CPM Assumptions/Limitations

• Project activities can be identified as entities.
  (There is a clear beginning and ending point for
  each activity.)
• Project activity sequence relationships can be
  specified and networked.
• Project control should focus on the critical path
• Project timing can be estimated

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Example in EPM where activities are days
Forward pass
Assume that activity starts in morning and ends
in evening
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Backward pass
EF
ES
LS
LF
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Critical path (Slack0)
Slack LS - ES
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Slack and duration
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Summary

• Finding dependencies of activities is very
  important in project management
• Creating a network diagram will assist in the
  planning of the the projects utilization of
  resources
• Focus must be on the critical path
• Gantt charts are most commonly used for planning,
  but they have limitations.

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Home work for Jan.24 and Jan.26

• Next class (Jan.24) homework The Campus wedding
  displayed on OH or Powerpoint and handed in.
• By Jan.26
• In MS Project
• WBS broken down to lowest level activities for
  Deployment
• Time estimates depicted in Gantt chart with
  interdependencies displayed
• Estimated resource requirements (note For the
  consulting company)
• Group1 Mingming, Mehmet, Bailey
• Group 2 Mei, Ryan, (Kevin)
• Group 3 Yurik, Ian