A Look Ahead

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A Look Ahead

• We will now turn our attention to several tools
  and techniques associated with Project Time
  Management
• First, we will consider
• PERT CPM Historical Perspective
• Overview of Sequencing Techniques
• ADM Arrow Diagramming Method
• Determining the Critical Path
• download ADM_Class_Example.doc

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A Look Ahead(continued)

• After that, we will continue our exploration of
  tools and techniques by considering
• The Concept of Float
• download ADM_Float_Calcs.xls
• Probabilistic Activity Duration Estimates
• download ADM_Mean_Variance.xls
• Probabilistic Project Completion
• download ADM_Standard_Normal_Table.xls

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PERT/CPMSome History

• PERT was first used in the late 1950s by the
  Navy for the Polaris Missile Program
• PERT gt Project Evaluation Review Technique
• Development was in conjunction with the
  consulting firm of Booz, Allen, and Hamilton
• Development was designed to meet the needs of the
  age of massive engineering
• The Navy was concerned with performance trends on
  large military projects.

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PERT/CPMSome History (continued)

• Virtually simultaneously CPM was developed by the
  duPont Company and Remington-Rand-Univac.
• CPM gt Critical Path Method
• For use on large construction projects
• Specifically targeted for process industries
• The two groups were unaware of each other's
  existence until about 1960.
• By then, each stood on its own merits

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PERT/CPMSome History (continued)

• PERTs strengths are in its use of probabilistic
  estimates of activity durations
• CPMs strengths are in its ability to do
  time-cost trade-offs
• Today, PERT/CPM are widely recognized as
  comprising one set of techniques
• the differences are primarily viewed as only of
  historical importance

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Activity SequencingDisplay Techniques

• There are many suitable techniques for displaying
  the sequence of activities involved in a project
• Gantt Charts
• Precedence Diagramming
• Arrow Diagramming
• Conditional Diagrams

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Gantt Charts

• Gantt charts use horizontal bars (or lines) to
  represent activities
• Gantt charts are more commonly used for schedule
  display than activity sequencing
• see BOK Figure 6-6 (1996 2000) for an example
• length of the bars show expected duration
• activity inter-relationships are not explicitly
  shown
• we will see Gantt Charts again when we consider
  Resource Loading Leveling

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The Precedence Diagramming Method

• The Precedence Diagramming Method (PDM) uses
  boxes to represent activities and arrows to
  represent dependencies
• see BOK Figure 6-2 (1996 2000 for an example
• This technique is also known as the
  Activity-on-Node (AON) Diagramming

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More on PDM

• Dependencies can include
• Finish-to-Start
• Finish-to-Finish
• Start-to-Start
• Start-to-Finish
• Dependencies are usually indicated by the
  placement of the arrow heads and tails relative
  to the nodes but no consistent approach has been
  universally adopted.
• Looping and Conditional Branching is not allowed

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The Arrow Diagramming Method (ADM)

• The Arrow Diagramming Method (ADM) uses the
  following conventions
• Arrows represent activities
• "Regular" activities require time and resources
• "Dummy" activities show precedence relationships
• Nodes represent events
• A point in time
• Some nodes may represent milestone events
• see BOK Figure 6-3 (1996 2000) for an example

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More on ADM

• Also known as Activity-on-Arrow (AOA)
• Each activity is represented by one and only one
  arrow in the network.
• Nodes (events) are numbered uniquely.
• Duplicate node numbers are not allowed
• No two activities can be identified by the same
  beginning and ending nodes.
• Dummy activities may be required

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More on ADM (continued)

• Before an activity can begin, all activities
  terminating at the activities beginning node must
  be completed.
• Neither the length of an activity arrow nor its
  compass direction have any significance.
• Networks should (must) have only one initial
  event and one terminal event.

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An Example to TryDraw an Arrow Diagram

• A project consists of Activities A, B, C, D, E,
  F, G, H, I, J, K, and L
• A, B, and C, the 1st activities of the project,
  can start simultaneously
• A and B precede D
• B precedes E, F, and H
• F and C precede G
• E and H precede I and J
• C, D, F, and J precede K
• K precedes L
• I, G, and L are terminal activities for the
  project

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Lets Examine the Example Solution

• Solution to be shown in class.

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Conclusion of Sequencing Techniques

• Well return to ADM in just a few minutes but
  first lets complete the set of sequencing
  techniques by considering Conditional Diagramming

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Conditional Diagramming

• Conditional Diagramming methods allow for
  probabilistic activities and looping
• neither of these are allowed in traditional PDM
  or ADM
• Conditional diagramming techniques include
  Graphical Evaluation and Review Technique (GERT)
  and System Dynamics
• these are beyond the scope of this course

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Activity Durations

• The next logical step in Project Time Management
  is to determine activity durations.
• We are going to defer a detailed discussion of
  estimating activity durations until later in the
  course.
• At this point we need to introduce the concept of
  the Critical Path of a project.

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The Concept of the Critical Path

• The determination of the start and completion
  time of each activity on the network diagram
  requires a special calculation procedure.
• This approach classifies each activity as either
  critical or non-critical.
• The approach is commonly known as the Critical
  Path Method

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The Concept of the Critical Path (continued)

• A delay in the start or completion of a critical
  path activity will cause a delay in the
  completion of the entire project.
• Non-critical path activities can absorb some
  delay in start or completion without impacting
  project completion.
• The amount of delay which can be absorbed is
  known as slack or float.

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The Concept of the Critical Path (continued)

• There will always be at least one sequence of
  activities from the initial node to the terminal
  node that is made up entirely of critical
  activities.
• This is known as the Critical Path of the
  Project.
• Any delay of a critical path activity will delay
  the completion of the project.

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The Concept of the Critical Path (continued)

• The critical path defines the minimal completion
  time for the project.
• Multiple critical paths are possible.
• Complete multiple critical paths
• two or more critical paths exist from the initial
  node to the terminal node of the project.
• rare in uncrashed networks, common in fully
  crashed
• Partial multiple critical paths
• two or more sets of parallel activities are
  critical over some segment of the project.
• relatively common

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Determining the Critical Path

• The critical path is found by a two phase
  methodology after activity durations have been
  determined.
• A forward pass is made through the network
  diagram to determine the earliest start time for
  each node.
• A backward pass is made through the network to
  determine the latest completion time for each
  node.

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Determining the Critical Path (continued)

• This is best illustrated through an example.
• Mathematical details in SPM_PERTCPM_Math
• An ADM diagram for a project is shown on the
  following page
• the activities themselves are not labeled, we
  will use the (start node, end node) pair to
  uniquely identify activities (e.g., (0,1))
• duration estimates are indicated

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Class ExampleCritical Path Calculations
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Forward Pass and Backward Pass

• Solution to be shown in class.

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The Critical Path

• An activity lies on the critical path if it meets
  the three following conditions
• The earliest start and latest completion for the
  activitys terminal node are equal
• The earliest start and latest completion for the
  activitys initial node are equal
• The difference between the earliest start of the
  terminal node and the earliest start of the
  initial node is the activity duration.

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The Critical Path(continued)

• Lets re-examine the example for the critical
  path.
• Solution to be shown in class.

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