Download Lecture #4

Software Project
Management
Resource availability and
critical chain
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Glenn Booker
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Lecture #4
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Resource Availability
 To make a project schedule complete,
resources need to be assigned to
each task
 Need to identify the number of
resources, and their roles
 3 senior programmers
 0.1 program manager
 1 database analyst, etc.
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Resource Availability
 Now we need to determine if the
project can be completed with the
resources available
 The key is to balance the resources
with the tasks they need to
accomplish – some refinement of the
tasks and activities in the project is
often needed
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Leveling Resources
 Resource assignments are generally
done task-by-task at first
 Then need to add up the planned
resources and look for potential
problems
 Over committing people
 Resources inconsistent with project
priorities
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Leveling Resources
 Lack of management to monitor the
project resources
 Lack of accounting for employee
turnover
 Leveling should result in no resource
being planned to work more than
100% of the time
 And we want a logical flow of resources
needed – no wild fluctuations
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Leveling Resources
 No schedule is typically perfect – we
want to get reasonably close however
 Strategies to level resources include
 Use available schedule slack
 Shift the project finish date
 Smoothing
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Use available schedule slack
 Slack is the amount of time a task’s
start or completion could be changed
without affecting project completion
 Hence we can slide tasks left & right
on the schedule within the limits of
their slack time to smooth out
resource needs
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Shift the project finish date
 If the completion date isn’t critical,
consider moving it to the right (later)
in order to avoid resource conflicts
(multiple tasks needing the same
resource at once)
 Otherwise might need to reduce the
project scope to eliminate conflicting
tasks, or defer feature completion to
later releases
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Smoothing
 Here, smoothing refers to deliberately
planning people to work overtime to
accomplish certain tasks
 Done by scheduling >8 hours of work
per day, or using weekends and/or
holidays as work days
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More Approaches
 Other ways to help smooth the
resource needs include
 Decompose activities into smaller tasks,
and spread out when those tasks are
done
 Stretch the duration of tasks, thereby
reducing the number of resources
needed
 Use less skilled resources, and extend
the schedule for the task accordingly
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Cost of Resource Leveling
 Often leveling or smoothing resources
can lead to a longer project schedule
 This may increase the cost of the
project, particularly if fixed project costs
are affected (e.g. facility rent)
 More direct costs could include failure to
earn early completion incentives, or
penalties for late project completion
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Micro-level Planning
 It’s possible to plan subtasks to a
very fine amount of detail (day or two
subtask task durations)
 This can be a good strategy for
understanding serious estimation
problems
 In general, however, the added cost
of planning and tracking isn’t worth it
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Work Packages
 Earlier we defined a project as having
activities, which are broken into tasks
 A way to describe and manage the
tasks within an activity are work
packages
 The work package describes the tasks
to be accomplished, relevant dates,
and who will do the work
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Work Packages
 Sometimes a work package is also a
contractual mechanism to describe a
chunk of work to be accomplished
 The manager of a work package is
responsible for managing the tasks
needed to get the work done, and report
the time and effort needed, and the work
package’s status
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Work Packages = Insurance
 The work package can also be seen
as insurance to describe the work in
enough detail to help recover if
turnover is a problem
 During the peak of the dot-com boom,
this would have been a very wise
strategy to follow
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Work package assignment (p. 155)
WP WP
#
Name
A
Design
B
C
D
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Product
eval
Place
locate
Product
forecast
Early
Start
3/4/0
5
Etc.
Late
WP
Finish Manager
4/1/0 F Smith
5
Lecture #4
Contact
info
3455678
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Work Packages
 The list of all work packages are
summarized, like shown on the
previous slide
 Then each work package (A, B, etc.) is
described in task-level detail using the
form on page 156 of the text
 Notice that several fields in the top of
the form come from the main
schedule – predecessors, successors,
critical path, etc.
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WP Implications on schedule
 Whether you use work packages has
strong implications on the level of
detail that appears in your master
schedule
 If using work packages, you could plan
to the activity level, and leave the details
of each activity to the work package
managers to define
 If not using work packages, the main
schedule needs to plan to the task level
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Complete Project Plan
 With the project defined to the task
level you have enough detail to
estimate the labor costs, and are able
to provide a complete project
proposal to upper management for
approval to proceed
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Critical Chain Project Management
 Critical Chain Project Management
(CCPM) is another approach to
managing resource conflicts
 Key additional reference is “Critical
Chain Project Management” by L. Leach,
ISBN 1580539033
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Critical chain vs. critical path
 The critical path is the longest
duration through the project
 Doesn’t consider the resources needed
for tasks along the critical path
 Critical chain is the longest path
through the project, considering both
task dependencies and resource
constraints
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How is CCPM different?
 CCPM is based partly on some
statistical concepts
 The duration of any task will vary,
depending on various reasons
 Those reasons could be due to common
causes (normal random fluctuations) or
special causes (specific causes which
could be identified)
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Common & Special Causes
 Common causes are accounted for in
the contingency planning for each
task – the amount of time needed to
ensure it’s completed on time
 Special causes are dealt with as part
of risk management
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Plan for 50% Completion Time
 Normally we plan each task so that
90% of the time we’d finish on time
 This includes a lot of time for each task
compared to the 50% completion time
(the task time we’d finish in 50% of the
time)
 CCPM plans for the 50% completion
time, and adds the additional time as
contingency time
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Figure 12.1, page 254
 This is what the cited figure means –
the white part of each task is the time
needed to finish it 50% of the time
 The grey part is the difference between
90% and 50% completion times
 In CCPM we lump the 50% times
together, and lump the grey parts
into a contingency time period
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Notice the assumption
 The text assumes that the difference
between 90% and 50% completion
times is very large – typically half of
the planned duration
 So tasks with a 90% duration of 6
days, have a 50% duration of 3 days
 Is this realistic?
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To create a critical chain path
1. Start with the early schedule from
traditional project management
(TPM); figure 12.2, the critical path
is tasks C1-C2-C3
2. Replace the 90% completion times
with 50% completion times for every
task
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To create a critical chain path
3. Convert the early schedule to the
late schedule, and show resources;
the late schedule is shown in Fig 12.3
4. Look for resource conflicts, and
adjust the start time for each task
(here it’s assumed each person can
work one task at a time)
5. Add time buffers
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Time Buffers
 Buffers are time intervals added to
the end of a series of tasks to allow
for contingencies
 Buffers can be used for many reasons
 Project buffers
 Feeding buffers
 Resource buffers
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Project buffers
 Project buffers are at the end of a
critical chain, to protect the overall
project schedule (allow for general
contingencies)
 If T50i is the 50% completion time for
task i on the critical chain, T90i is the
90% completion time for task i, then
project buffer = sqrt{ S (T90i – T50i)2 }
i
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Feeding buffers
 A feeding buffer is a buffer at the end
of a series of tasks which feed into
the critical chain (like a stream which
feeds a river)
 It is calculated the same as a project
buffer
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Resource buffers
 A resource buffer isn’t a time buffer
at all; it’s a flag to warn that a
particular resource will be needed
soon
 So it’s an alarm clock!
 A resource buffer is established some
time interval before the resource is
needed (1 week, a month, etc.)
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Return to CCPM example
 Resume the example from slide 28
 Add feeding buffers onto the end of tasks
A1-A2 and B1-B2 (since they feed the
critical chain C)
 Add project buffer onto the end of tasks
C1-C2-C3 (since it is the critical chain)
 Notice that resource conflicts aren’t
considered for buffer time periods
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Return to CCPM example
 The project which was 16 days
originally (under TPM) is 13.7 days
using CCPM
 A schedule reduction of 14%
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Managing a project using CCPM
 Since the nominal task duration is
only met 50% of the time, there have
to be careful rules for managing the
buffers
 Three levels of warning are
established
 When the first, second, and final thirds
of the buffer are entered
 None for when the buffer is exceeded?
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Managing a project using CCPM
 How seriously each of these warnings
is treated depends on how far into
the series of tasks you are when the
buffer is used
 Again using a scale of first, second, and
final third of the tasks accomplished
 This produces the chart on page 261
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Managing a project using CCPM
 So if a series of tasks is 15 days long,
and has a 10 day buffer
 If you are 8 days into the buffer after
completing 7 days of the tasks’ work
 The tasks are 7/15 into the work, which is
the second third of the tasks
 The buffer used is 8/10, which is the final
third of the buffer
 Hence the diagnosis is “Serious problem;
implement the solution”
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CCPM Summary
 So CCPM uses a little statistics, and
a little risk management theory to
reduce the planned schedule for
completing a project
 Several examples of success using
CCPM are cited
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