Introduction
Over the years, a number of useful tools have been developed to help
projects get done quicker, easier, and more effectively.
How are these tools affected by Critical Chain Project Management ( CCPM
) ?
How do these traditional project management tools effect, interact,
assist Critical Chain Project Management (CCPM) methods ?
Critical Path Method ( CPM )
Critical Path Method ( CPM ) logically connects tasks together in
predecessor and successor relationships. Slack time in a schedule can be
left to occur as it happens, or specifically managed.
When managing slack time, project managers typically push all tasks to
either:
- the latest possible start date without causing a later finish of
the entire project (ie. Just-in-Time, or "backwards" scheduling).
- the earliest possible start date for all tasks. This works well
for tasks and projects where there is a great uncertainty or risk. In
this way, we get into the details quickly, and learn how big a problem
we have. The sooner we learn the true scope (rather than guesses &
opinions), the sooner we can construct a more realistic plan. For
other situations, this causes many low priority tasks to "clog up" the
available resources. If everything is important, nothing is important.
We soon lose focus on the essential critical tasks. Much activity is
occurring, but the project moves forward more slowly.
- A mixture of the above philosophies based on highly variable logic,
expertise, and opinion.
Most CPM schedules are scheduled in forward manner using ASAP (AS Soon
as Possible) task scheduling. This is where traditional project methods
and CCPM are most visibly different.
With CCPM, we use backwards scheduling, but add "safety
buffers" to the schedule. This allows for the delays and
unknown or unknowable problems that will surely occur.
Where do we get the extra time from with which to create the Safety
Buffers? We get it by trimming most task duration estimates by 50%.
People naturally pad their task estimates to add for delays starting,
unforeseen problems, unavailable resources, and multi-tasking (ie. being
asked to do 2 or more tasks at the same time, rather than completing the
first, then starting the second, and so on.). In this way, we take the
safety time out of each task, and pool it together into the Safety
Buffers.
There are 4 different types of Safety Buffers (project, resource, drum,
and capacity). Each of thes safety buffers has a specific and unique
purpose, but all of them work together to produce the optimum schedule.
Further discussions on these buffers is beyond the scope of this brief
introduction to CCPM. For more information, we suggest our
CCPM Introduction Course.
Gantt charts
Gantt charts have been around since the 1900's, and are still one of
the most useful tools for visualizing a project. With Gantt charts,
tasks are represented by bars of different length; length being
proportional to the planned task duration. Lines &/or arrows between the
bars show the relationships between the task (ie. precedence &
successors). With CCPM, Gantt charts are used the same way, with
only a few policies different than traditional project methods.
PERT charts
PERT is where the task information is inside a box with arrows between
the boxes showing how the tasks are connected and related. PERT has been
around since the 1950's, and is still one of the most useful tools for
visualizing a project. With CCPM, PERT tools are used the same
way, with only a few policies in how they are constructed and used which
are different than traditional project methods.
Work Breakdown Structure (WBS)
Work Breakdown Structure (WBS) shows a hierarchial view and
relationship between project, phases, deliverables, tasks, and sub-tasks.
With CCPM, milestones are minimized or avoided if at all
possible. Funnels and diamonds are a sign that someone has planned the
project with traditional methods, rather than CCPM. WBS can be
somewhat limiting and conflicting with CCPM as WBS tends to be a
powerful magnet to the old way of thinking. However, there is no
fundamental conflict between WBS and CCPM; only that old habits
die hard.
Earned
Value (EV)
Earned Value (EV) shows the dollar equivalent of the work planned and
completed, and can be readily compared for plan vs. actual. While there
is no fundamental conflict between EV and CCPM; old habits die
hard. EV can be somewhat limiting and conflicting with CCPM as EV
tends to be a powerful magnet to the old way of thinking.
It would be unfair to measure project personnel using one system (ie.
EV), while running the project day-to-day using a different system (ie.
CCPM). Some clients, especially the Defense Industry, are insistent
on EV. One effective approach is to run the project using CCPM,
then produce a month-end EV report to keep the customer happy.
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