Creating the Project Plan
The Plan versus a Schedule
• The plan
–
–
–
–
Defines the activities
Documents the interaction between activities
Estimates the duration for completing each activity
Analyzes the sequences, duration and resource
requirements to crate a project schedule
• The schedule
– Determine start and finish dates for project activities
– Often must be iterated(along with processes that are the
input) especially the duration estimating
Project Planning Techniques
• Provide regular status updates to stakeholders
• Include team members in planning sessions and plan preparation
• Provide various alternatives to management
– Scope constrained alternatives
– Time constrained alternatives
– Resources alternatives
• Plan to plan
• Obtain plan approval before beginning execution
Work Products for Planning
Task List
Work Breakdown
Structure
Precedence
Graph
CPM Diagram
Gantt Chart
Getting the Planning Process Started
Product List
Optional: for a product-oriented project, it
may be useful to begin with a product list
Task List
Work Breakdown
Structure
•
•
Planning depends on estimates of
the work required and the way it
will be organized.
The planning process is driven by
the project objectives
From Task List to WBS
Task List
Task
Task
Task
Task
Task
Task
A
B
C
D
E
F
WBS
Overall Task
SubTask 1
Task C
Task A
Task E
SubTask 2
Task B
SubTask 2.1
Task F
Task D
add management
WBS as an Estimation Tool
Bottom-Up Estimating
• Effort for smaller tasks can be more accurately estimated than larger
ones
• Estimate all the “primitive” tasks first (those at the bottom of the
WBS – with no subtasks of their own). PMBOK * calls these work
packages.
• Combine these estimates to get an overall estimate or estimates for
major subtasks
• Track actuals against estimates at the task level to improve your
estimating skills
• Use this data to create a useful experiential estimation database
Project Management Book of Knowledge
Precedence Graph
• The precedence graph captures predecessor or
sequencing information for all tasks in the WBS
• Used as an intermediate step toward a CPM diagram
• The process used to create the precedence graph is
referred to as PDM (Precedence Diagram Method) in
the PMBOK.
Work Breakdown
Structure
Precedence
Graph
Precedence Graph
Activity P
Activity M
Activity O
Activity Q
Activity S
Activity N
Activity R
Activity N must complete before Activity R can
begin, and so on.
Effort and Duration
• CPM (Critical Path Method) Diagrams are
derived from Precedence Graphs
• To accomplish this, we must translate effort
estimates into duration estimates
• Effort defines the total required number of time
units (often measured in hours) to complete a
task
• Duration refers to the calendar time (often in
days or weeks) required to complete task
Effort and Duration (cont’d)
• Effort is distributed over a duration
• This is done by assigning some particular
number of persons to the task at various
times
• Or, we can assign percentages of one or
more persons’ time to the task at various
times
Effort, Duration, and Resource Allocation
• For example, a 750 hour effort would have a 10-week
duration if 2 persons were allocated to it fulltime
(assuming a fulltime week = 37.5 hours) for that
period
• However, this same effort could result in drastically
different durations, with different resource
allocations:
– 40 weeks – if 50% of a person’s time is allocated to it
– 20 weeks -- if 1 person is allocated to it fulltime
– 15 weeks -- with1 person fulltime for 10 weeks, then 2
persons fulltime for the next 5 weeks
– 5 weeks – with 4 persons allocated to it fulltime
Effort, Duration, and Resource Allocation (cont’d)
It is important to remember that the required effort is just one
factor that goes into making a duration estimate.
We’ve all heard it:
If one woman can produce a baby in 9 months, how
soon can 9 women produce a baby?
Effort, Duration, and Float (Slack)
• If we allocate resources so that a task is
completed before it is absolutely necessary for
all the other task(s) waiting for it to complete,
we say that we have built float or slack time
into our schedule
• Float adds flexibility to a project’s schedule and
hence it is important to recognize when it is
possible
• The Critical Path Method (CPM) Diagram
captures this feature of a project
CPM Diagrams
According to the PMBOK:
PMBOK View
“The Critical Path Method (CPM) is a network analysis technique used to
predict project duration by analyzing which sequence of activities (which
path) has the least amount of scheduling flexibility (the least amount of
float). Early dates are calculated by means of a forward pass, using the
specified start date. Late dates are calculated using a backward pass,
starting from a specified completion date – usually the forward pass
calculated project early finish date.”
Adding More Information to the Precedence Graph –
CPM Diagrams
Earliest
Start
Earliest
Finish
Task
Duration
Float
Latest
Start
Latest
Finish
Add this information for each node
in the Precedence Graph
Precedence
Graph
CPM Diagram
Terms for CPM Diagrams
For each node:
• D = Estimated Duration
• ES = Early Start Date
ES = Earliest finish time for all preceding events
• EF =Early Finish Date
EF = ES + D
• LF =Late Finish Date
LF = Latest start time of all succeeding events
• LS =Late Start Date
LS = LF - D
• F = Float
F = LF - EF OR F = LS - ES
• F = The time an activity’s start or finish can be delayed without
delaying project completion
Computing Terms for CPM
Diagram Nodes
• D is an estimate (must be known)
• Determine ES = Early Start
ES = Earliest finish time for all preceding events
• Determine LF =Late Finish
LF = Latest start time of all succeeding events
• Then we compute LS, EF, and F
CPM Diagram Nodes -- Example
early start
(determined by
earliest finish
for all preceding
activities)
duration
late start
(= 9 – 3)
2
early finish (= 4 + 3)
4 weeks
7 weeks
Task
1
3 weeks
6 weeks
2 weeks
3
9 weeks
float (= 9 – 7 or = 6 – 4)
late finish (determined
by the latest start for
all succeeding activities)
Add this type of information for each node
Method for Computing CPM Diagrams
• All activities must be assigned durations before you begin
• Start with the activities that have no preceding activities and assign
their early start times to be 0 (there may be only one of these)
• Work from left to right and compute the early start and early finish
times for all nodes – this is called the forward pass
• The largest early finish time will determine the minimum time for the
project to complete
• All activities with no succeeding activities will get this value as their
latest finish times (there may be only one of these). Assign each of
these activities to have 0 float
• Use this information to work from right to left assigning late finish
times and late start times for all nodes – this is called the backward
pass
• Now you can quickly compute float for all nodes
Team Activity 1: CPM Diagram
Consider the CPM Diagram (partial) given on the next slide
Complete the diagram by determining the missing
information for each node.
CPM Diagram – Partial Example
Critical Paths
• If an activity that has 0 float slips, the
entire project will slip by that amount
• This is why activities that have 0 float are
said to be on a critical path
• There may be multiple critical paths for a
project
• Many practitioners establish some
threshold amount of float (suitably small)
and compute near-critical paths as well
Critical Paths (cont’d)
• Note that critical (and near-critical) paths
are dynamic and change as the actual (as
opposed to estimated) schedule unfolds
• Critical (and near-critical) paths must be
recomputed each time there is an activity
slippage anywhere in the schedule that is
larger than that activity’s float
Why Compute Critical Paths?
• Can be used to focus resources and attention more
efficiently and effectively
• Best resources can be assigned to critical path activities
• Allows project manager to monitor crucial activities more
closely
• Helps prioritize risks, so risk mitigation activities can be
focused on the most important potential risk events
• “Near-critical” tasks can also be identified and tracked
Why Compute Critical Paths? (cont’d)
• Schedule “emergencies” can be addressed by
“crashing” or fast-tracking critical path activities
• Crashing means compressing activity duration
• Fast-tracking means doing things in parallel
• Danger in crashing or fast-tracking is increased
risk
Team Activity 2: Critical Paths
Consider the CPM Diagram you completed in the
previous activity.
1) What is the shortest possible duration for the project?
2) Identify the critical path (or paths).
Consider questions 3 and 4 independently of each other.
3) If Procurement slips 3 weeks, what is the impact on the project
duration? What happens to the critical path
4) If Beta Test slips 2 weeks (with no other slippage), what is the impact
on the project duration?
Team Activity #3
• A project has been defined to contain the following list of activities along with
their required times for completion
1. Draw a CPM diagram for the activities
2. Calculate the earliest completion time
3. Show the critical path
4. What would happen if activity 6 were revised to take 6 weeks instead of
1 week
Activity
Immediate activity
Weeks
Predecessors
1
Collect requirements
2
-
2
Analyze processes
3
1
3
Analyze data
3
2
4
Design processes
7
2
5
Design data
6
2
6
Design screens
1
3, 4
7
Design reports
5
4, 5
8
Program
4
6. 7
9
Test and document
8
7
10
Install
2
8,9
Team Activity #4
• Look at the activities outlined in Team Activity 3 (see
below). Assume that your team is in its first week of the
project and has discovered that each of the activity duration
estimates is wrong. Activity 2 will take only 2 weeks to
complete . Activity 4 and 7 will each take three times longer
than anticipated. All other activities will take twice as long
to complete. In addition a new activity, number 11Feedback, has been added. It will take 1 week to complete
and its immediate predecessors are activities 10 and 9.
1. Adjust the CPM diagram and
2. Recalculate the earliest expected completion time
Gantt Charts
• Created from CPM diagrams
• Capture scheduling information in a bar
chart format
• Dynamic Gantt charts (that is, those that are
updated frequently) are an excellent tool to
ascertain the status of a project at a given
time
• Good tool for estimating resource needs in a
given time frame
CPM Diagram
Gantt Chart
Gantt Charts – An Example
date (week #)
tasks
1
2
3
4
5
6
7
8
T1
critical
path
T2
T3
T4
T5
float
Team Activity #5: Gantt Chart
Construct a Gantt chart for your CPM diagram created in
Activity 3
1) Create a Gantt chart from your CPM Diagram.
2) What kind of resources do you anticipate needing in week 6?
3) Can you tell how many resources you will need of each
type/category? Hint: Are duration and effort the same?