4. Background
Schedule is the conversion of a project action
plan into an operating timetable
Basis for monitoring a project
One of the major project management tools
Work changes daily, so a detailed plan is
essential
Not all project activities need to be scheduled at
the same level of detail
5. Background Continued
Most of the scheduling is at the WBS
level, not the work package level
Only the most critical work packages may
be shown on the schedule
Most of the scheduling is based on
network drawings
6. Network Scheduling Advantage
Consistent framework
Shows interdependences
Shows when resources are needed
Ensures proper communication
Determines expected completion date
Identifies critical activities
7. Network Scheduling Advantage
Continued
Shows which of the activities can be
delayed
Determines start dates
Shows which task must be coordinated
Shows which task can be run parallel
Relieves some conflict
Allows probabilistic estimates
8. Network Scheduling Techniques: PERT
(ADM) and CPM (PDM)
PERT was developed for the Polaris
missile/submarine project in 1958
CPM developed by DuPont during the same
time
Initially, CPM and PERT were two different
approaches
– CPM used deterministic time estimates and allowed
project crunching
– PERT used probabilistic time estimates
Microsoft Project (and others) have blended
CPM and PERT into one approach
9. Terminology
Activity - A specific task or set of tasks
that are required by the project, use up
resources, and take time to complete
Event - The result of completing one or
more activities
Network - The combination of all
activities and events that define a project
– Drawn left-to-right
– Connections represent predecessors
10. Terminology Continued
Path - A series of connected activities
Critical - An activity, event, or path
which, if delayed, will delay the
completion of the project
Critical Path - The path through the
project where, if any activity is delayed,
the project is delayed
– There is always a critical path
– There can be more than one critical path
11. Terminology Continued
Sequential Activities - One activity must
be completed before the next one can
begin
Parallel Activities - The activities can
take place at the same time
Immediate Predecessor - That activity
that must be completed just before a
particular activity can begin
12. Terminology Continued
Activity on Arrow - Arrows represent
activities while nodes stand for events
Activity on Node - Nodes stand for
events and arrows show precedence
14. Constructing the Network
Begin with START activity
Add activities without precedences as
nodes
– There will always be one
– May be more
Add activities that have those activities as
precedences
Continue
15. Gantt (Bar) Charts
Developed by Henry L. Gantt
Shows planned and actual progress
Easy-to-read method to know the current
status
16. Advantages and Disadvantage
Advantages
– Easily understood
– Provide a picture of the current state of a
project
Disadvantage
– Difficult to follow complex projects
25. Exercise: How long will this project take?
What is the critical path?
Task Time Dependency
A 5 days None
B 3 days A
C 8 days A
D 3 days B
E 4 days C, D
F 3 days C, D
G 9 days D, E
H 6 days B, E
I 3 days F, G
J 7 day H, I
26. Revised time to completion
A key technical expert who is needed for
step D had to travel to fix a customer crisis
just as step D started.
The expert will return in 7 days.
What is the impact on the project’s
completion date?
35. Uncertainty of Project Completion Time
Assume activities are statistically
independent
Variance of a set of activities is the sum
of the individual variances
Interested in variances along the critical
path
36. Example
45
.
52
645
.
1
745
.
5
43
22
.
1
745
.
5
7
33
43
50
)
(
2
Z
D
D
Z
37. Toward Realistic Time Estimates
Calculations are based on 1% chance of
beating estimates
Calculations can also be based on 5% or 10%
Changing the percentage requires changing the
formulae for variance
When using 5%, the divisor changes to 3.29
When using 10%, the divisor changes to 2.56
39. Critical Path Method—Crashing a
Project
Time and costs are interrelated
Faster an activity is completed, more is
the cost
Change the schedule and you change the
budget
Thus many activities can be speeded up
by spending more money
40. What is Crashing / Crunching?
To speed up, or expedite, a project
Of course, the resources to do this must be
available
Crunching a project changes the schedule for
all activities
This will have an impact on schedules for all the
subcontractors
Crunching a project often introduces
unanticipated problems
50. Fast-Tracking
Fast-tracking is another way to expedite a
project
– Mostly used for construction projects
– Can be used in other projects
Refers to overlapping design and build
phases
Increases number of change orders
Increase is not that large
51. The Resource Allocation Problem
CPM/PERT ignore resource utilization
and availability
With external resources, this may not be
a problem
It is, however, a concern with internal
resources
Schedules need to be evaluated in terms
of both time and resources
52. Time Use and Resource Use
Time limited: A project must be finished
by a certain time
Resource limited: A project must be
finished without exceeding some specific
level of resource usage
System-constrained: A project has fixed
amount of time and resources
53. Resource Loading
Resource loading describes the amount
of resources an existing schedule
requires
Gives an understanding of the demands a
project will make of a firm’s resources
56. Resource Leveling
Less hands-on management is required
May be able to use just-in-time inventory
Improves morale
Fewer personnel problems
When an activity has slack, we can move
that activity to shift its resource usage
57. Resource Leveling Continued
May also be possible to alter the
sequence of activities to levelize
resources
Small projects can be levelized by hand
Software can levelize resources for larger
projects
Large projects with multiple resources are
complex to levelize
58. Constrained Resource Scheduling
Heuristic
Approach
An approach, such as a
rule of thumb, that yields
a good solution that may
or may not be optimal
Optimization
Approach
An approach, such as
linear programming, that
yields the one best
solution.
59. Heuristic Methods
They are the only feasible methods used
to attack large projects
While not optimal, the schedules are very
good
Take the CPM/PERT schedule as a
baseline
60. Heuristic Methods Continued
They sequentially step through the
schedule trying to move resource
requirements around to levelize them
Resources are moved around based on
one or more priority rules
61. Common Priority Rules
As soon as possible
As late as possible
Shortest task first
Most resources first
Minimum slack first
Most critical followers
Most successors
Arbitrary
62. Heuristic Methods Continued
These are just the common ones
There are many more
The heuristic can either start at the
beginning and work forwards
Or it can start at the end and work
backwards
63. Optimization Methods
Finds the one best solution
Uses either linear programming or
enumeration
Not all projects can be optimized
64. Multi-Project Scheduling and Resource
Allocation
Scheduling and resource allocation
problems increase with more than one
project
The greater the number of projects, the
greater the problems
One way is to consider each project as
the part of a much larger project
65. Multi-Project Scheduling and Resource
Allocation Continued
However, different projects have different
goals so combining may not make sense
Must also tell us if there are resources to
tackle the new projects we are
considering
67. Schedule Slippage
The time past a project’s due date
Slippage may cause penalties
Different projects will have different
penalties
Expediting one project can cause others
to slip
Taking on a new project can cause
existing projects to slip
68. Resource Utilization
The percentage of a resource that is
actually used
We want a schedule that smoothes out
the dips and peaks of resource utilization
This is especially true of labor, where
hiring and firing is expensive
69. In-Process Inventory
This is the amount of work waiting to be
processed because there is a shortage of
some resource
Similar to WIP in manufacturing
Holding cost is incurred
70. Heuristic Techniques
Multi-projects are too complex for
optimization approaches
Many of the heuristics are extensions of
the ones used for one project
71. Additional Priority Rules
Resource scheduling method
Minimum late finish time
Greatest resource demand
Greatest resource utilization
Most possible jobs
72. Goldratt’s Critical Chain
1. Thoughtless optimism
2. Capacity should be equal to demand
3. The “Student Syndrome”
4. Multitasking to reduce idle time
73. Goldratt’s Critical Chain Continued
5. Assuming network complexity makes no
difference
6. Management cutting time to “motivate”
workers
7. Game playing
8. Early finishes not canceling out late
finishes
