Developing a Project Plan
Ch 6, Ch 10, Ch 11, Ch 12, Ch 14
6–1
Developing the Project Plan
• The Project Network
–A flow chart that graphically depicts the sequence,
interdependencies, and start and finish times of the
project job plan of activities that is the critical path
through the network.
• Provides the basis for scheduling labor and equipment.
• Enhances communication among project participants.
• Provides an estimate of the project’s duration.
• Provides a basis for budgeting cash flow.
• Identifies activities that are critical.
• Highlights activities that are “critical” and can not be delayed.
• Help managers get and stay on plan.
6–2
Developing the Project Plan
• The project network is the tool used for planning,
scheduling, and monitoring project progress.
• The network is the framework for the project information
system that will be used by the project managers to make
decisions concerning project time, cost, and performance.
• Once the network is developed, it is very easy to modify or
change when unexpected events occur as the project
progresses.
• The network is developed from the information collected for
the WBS and is a graphic flow chart of the project job plan.
• Work packages from the WBS are used to build the
activities found in the project network.
6–3
From WBS/Work Packages to Network
• An activity can include one or more work packages.
• The activities are placed in a sequence that provides for
orderly completion of the project.
• Networks are built using nodes (boxes) and arrows
(lines).
• The node depicts an activity, and the arrow shows
dependency and project flow.
B
A
• Networks provide the project schedule by identifying
dependencies, sequencing, and timing of activities,
which the WBS is not designed to do.
• The primary inputs for developing a project network plan
are work packages.
6–4
Integration of
WBS and OBS
FIGURE 4.5
4–5
WBS/Work Packages to Network
FIGURE 6.1
6–6
WBS/Work Packages to Network
• The lowest level deliverable in Figure 6.1 is “circuit board.”
• The cost accounts (design, production, test, software)
denote project work, organization unit responsible, and
time phased budgets for the work packages.
• Each cost account represents one or more work packages.
• For example, the design cost account has two work
packages (D-1-1 and D-1-2)—specifications and
documentation.
• The software and production accounts also have two work
packages.
• Developing a network requires sequencing tasks from all
work packages that have measurable work.
6–7
WBS/Work Package to Network (cont’d)
FIGURE 6.1 (cont’d)
6–8
Constructing a Project Network
• Terminology
–Activity: an element of the
project that requires time.
A
–Merge Activity: an activity that
has two or more preceding
activities on which it depends.
B
–Parallel (Concurrent) Activities:
Activities that can occur
independently and, if desired,
not at the same time.
D
C
6–9
Constructing a Project Network (cont’d)
• Terminology
–Path: a sequence of connected, dependent activities.
–Critical path: the longest path through the activity
network that allows for the completion of all projectrelated 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
(Assumes that minimum of A + B > minimum of C in length of times to complete activities.)
6–10
Constructing a Project Network (cont’d)
• Terminology
–Event: a point in time when an activity is started
or completed. It does not consume time.
–Burst Activity: an activity that has more than one
activity immediately following it (more than one
dependency arrow flowing from it).
• Two Approaches
B
–Activity-on-Node (AON)
• Uses a node to depict an activity.
A
C
–Activity-on-Arrow (AOA)
• Uses an arrow to depict an activity.
D
6–11
Basic Rules to Follow in Developing
Project Networks
1. Networks typically flow from left to right.
2. An activity cannot begin until all preceding
connected activities are complete.
3. Arrows indicate precedence and flow
and can cross over each other.
4. Each activity must have a unique identifying number
that is greater than any of its predecessor activities.
5. Looping is not allowed.
6. Conditional statements are not allowed.
7. Use common start and stop nodes.
6–12
Activity-on-Node (AON) - Fundamentals
• An activity is represented by a node (box).
• The dependencies among activities are depicted by arrows between
the (boxes) on the AON network.
• The arrows indicate how the activities are related and the sequence in
which things must be accomplished.
• The letters in the boxes serve to identify the activities. In practice,
activities have identification numbers and descriptions.
• The relationships can be found by answering three questions for each
activity:
– Which activities must be completed immediately before this
activity? These activities are called predecessor activities.
– Which activities must immediately follow this activity? These
activities are called successor activities.
– Which activities can occur while this activity is taking place? This is
known as a concurrent or parallel relationship.
6–13
Activity-on-Node Fundamentals
FIGURE 6.2
6–14
Activity-on-Node Fundamentals (cont’d)
FIGURE 6.2 (cont’d)
6–15
Network Information
TABLE 6.1
6–16
Koll Business Center—Partial Network
FIGURE 6.3
6–17
Koll Business Center—Complete Network
FIGURE 6.4
6–18
Benefits of Graphical Networks
• It shows a graphical map of the project activities with
sequences and dependencies.
• The addition of time to the network allows us to:
– estimate how long the project will take.
– When activities can or must start.
– when resources must be available
– which activities can be delayed
– when the project is estimated to be complete.
– necessitates early assessment of resource needs in terms of
material, equipment, and people.
• In essence the project network with activity time
estimates links planning, scheduling, and controlling of
projects.
6–19
Network Computation Process
• Forward Pass—Earliest Times
–How soon can the activity start? (early start—ES)
–How soon can the activity finish? (early finish—EF)
–How soon can the project finish? (expected time—ET)
• Backward Pass—Latest Times
–How late can the activity start? (late start—LS)
–How late can the activity finish? (late finish—LF)
–Which activities represent the critical path?
–How long can activity be delayed? (slack or float—SL)
6–20
Network Information
TABLE 6.2
6–21
Activity-on-Node Network
FIGURE 6.5
6–22
Activity-on-Node Network Forward Pass
(ES + DUR = EF)
FIGURE 6.6
6–23
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.
• Stated differently, the forward pass assumes
every activity will start the instant in time when
the last of its predecessors is finished
6–24
Backward Pass Computation
• The backward pass starts with the last project
activity(ies) on the network. You trace backward on each
path subtracting activity times to find the late start (LS)
and finish times (LF) for each activity.
• 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.
6–25
Activity-on-Node Network Backward Pass
(LF - DUR = LS)
FIGURE 6.7
6–26
Determining Slack
– Is the amount of time an activity can be delayed after the start of a
longer parallel activity or activities.
– Is how long an activity can exceed its early finish date without
affecting early start dates of any successor(s).
– Allows flexibility in scheduling scarce resources.
– If slack of one activity in a path is used, the ES for all activities that
follow in the chain will be delayed and their slack reduced.
– Use of total slack must be coordinated with all participants in the
activities that follow in the chain.
– After slack for each activity is computed, the critical path(s) is (are)
easily identified. When the LF = EF for the end project activity, the
critical path can be identified as those activities that also have LF =
EF or a slack of zero.
– The critical path is the network path(s) that has (have) the least
slack in common.
6–27
Sensitivity
– The likelihood the original critical path(s) will change once the
project is initiated.
– The critical path is the network path(s) that has (have) the
least slack in common.
– Sensitivity is a function of the number of critical or nearcritical paths.
– A sensitive network would be one or more than critical paths
and/or noncritical activities with very little slack.
– Under these circumstances the original critical path is much
more likely to change once work gets under way on the
project.
– Project managers assess the sensitivity of their network
schedules to determine how much attention they should
devote to managing the critical path.
6–28
Activity-on-Node Network with Slack
(LS - ES = SL) or (LF - EF = SL)
FIGURE 6.8
6–29
Practical Considerations
–Conditional statements such as “if test
successful build proto, if failure
redesign” are not permitted.
–Looping is not allowed . It is an attempt
by the planner to return to an earlier
activity.
–Each activity needs a unique
identification code—usually a number.
–Laddering: Activities are broken into
segments so the following activity can
begin sooner and not delay the work.
6–30