Critical Path - Critical Chain Tracking of Projects

  • Thread starter Stuart @ Childrens Hospital
  • Start date
S

Stuart @ Childrens Hospital

Critical Chain is a variation of Critical Path; it adds resource leveling to
the critical path consideration. Tasks in a chain become critical if task
duration or resouce availability changes would cause a delay in the project
completion.

When I resource level in project, the tasks do not show up in the critical
path (view: Detail Gant) unless I set the task precedence. For a task group
(using only one resource each task) that should be on the critical path,
leveling does schedule the tasks to occur sequentially, but the group does
not show up as a critical path. I would like tot Detail Gantt to show this
is the critical path (or critical chain!).

Thank you
 
R

Rod Gill

Resource levelling and critical path calculations are two totally different
things in Project. For calculation of Critical path, manually entered dates,
task start and finish dates and links between tasks are the key inputs.
Resource information affects a task's finish date, but is not used in
critical path any other way.


--

Rod Gill
Project MVP
Visit www.msproject-systems.com for Project Companion Tools and more


"Stuart @ Childrens Hospital"
 
D

davegb

Rod said:
Resource levelling and critical path calculations are two totally different
things in Project. For calculation of Critical path, manually entered dates,
task start and finish dates and links between tasks are the key inputs.
Resource information affects a task's finish date, but is not used in
critical path any other way.


--

Rod Gill
Project MVP
Visit www.msproject-systems.com for Project Companion Tools and more
I believe you should be able to resource level and have Project still
track the CP. If not, what's the point of having them both? For years,
the CP was lost when you resource leveled. This glitch was fixed, to
the best of my knowledge, several versions back. I don't have a copy of
Project where I am, so I can't test it today. But it should be able to
do this!
 
R

Rod Gill

There are a lot of shoulds in this world and yes a solution can be achieved
that does it. The Project team have a limited time and limited head count
for each new version. This feature just hasn't made it to the top of the
list yet!
 
R

Realization

Stuart@ChildrensHospital said:
Critical Chain is a variation of Critical Path; it adds resource leveling to
the critical path consideration. Tasks in a chain become critical if task
duration or resouce availability changes would cause a delay in the project
completion.

When I resource level in project, the tasks do not show up in the critical
path (view: Detail Gant) unless I set the task precedence. For a task group
(using only one resource each task) that should be on the critical path,
leveling does schedule the tasks to occur sequentially, but the group does
not show up as a critical path. I would like tot Detail Gantt to show this
is the critical path (or critical chain!).

Thank you
 
C

Charlie A

Stuart,
You need to be able to highlight the Resource Critical Path, as
explained in Eric Eyttewaal's book, Dynamic Scheduling with MSP 2003.
By highlighting the RCP you will be able to keep an eye on tasks that
are either driven by logical dependencies (CPM) or by resource
dependencies.
In his book Eric explains a manual method for highlighting the RCP. As
well, a macro is available by license that will do this for you
automatically.
Yes, this is a feature that should be available in MSP. One of the very
big limitations of the CPM is that it does not take resource
vailability into account.

Charlie Ashmore
 
S

Steve House [Project MVP]

There's nothing incompatible between resource leveling and tracking the
critical path. True, the CP might CHANGE after resource leveling has
rescheduled and delayed some tasks in order to resolve their resource
overallocations but that's not the same thing as losing the CP. In fact, I
would interpret "tracking the CP" as meaning to accurately monitor the
ever-changing CP and always properly displaying whatever it currently may
be. The CP is that sequence of tasks that if delayed will cause the project
completion to be delayed. As such, it is a dynamic thing and not engraved
in granite at all. For example, after the project starts we have task A
lasting 5 days. It feeds two parallel tasks B 5 days and C 10 days. Those
two in turn feed into D 5 days and then on to the finish milestone. Your CP
is S->A->C->D ->F. Now the vendor for parts for task B informs you they're
on backorder and won't arrive until 15 days after the date originally
promised, ie, B's start is delayed 15 days. Now the CP is S->A->B->D->F.
Project tracks both of them perfectly - what it doesn't do is lock in the
first version of the CP as the only CP and continue to display it when the
CP has in fact transformed into the second one due to changing conditions.
Doing so simply would not be displaying reality. While I used what is a
SNET constraint situation for illustration purposes, it is in no way
different from a scenario where task B get's delayed by resource leveling
when the resource assigned to it was overallocated by conflicts caused by
the original schedule dates, the two cases are identical.
 
B

babe in the woods

Since this has been a few years, I thought I would give this thread a bump
with a few additional questions?

I would have assumed that MSPrpject would be able to identify the "new"
critical path after leveling - no luck. From what I am reading, it seems that
by definition, this new critical path is now called the critical chain. Is
this correct, or is this just MSProject's way of being able to say " nope -
we can provide the critical path, what you want is the critical chain".

For example - simple theoretical case:
Two tasks: one four days, and one five days. No links
Critical path is the five day task.
Now we assign the same resource to them both and level.....
tasks will be performed sequentially, but project still calls the five day
task as the critical path. Seems to me by simple definition of "critical
path" both tasks are on it?!?!

Anyhow - enough griping about the problem.... SOLUTIONS?!?!
Has anyone come up with some simple "free" macros, or custom
columns/formulas to help MSProject identify the new critical path/chain?!?!

...."babe in the woods"
 
B

babe in the woods

Hey Trevor - thanks for the speedy reply......

Please don't intrepret this as being confrontational, but let me try to
explain what I am trying to do, and why I was hoping the CPM feature in the
software could do what I was hoping to do...

I have started with a work breakdown structure for the entire project, and
then proceeded to put in all of the "hard links" - tasks that are
neccessarily required as successors or predecessors.

At this stage, I was able to turn on the critical path, and low and behold,
there it was - a line of tasks from start to finish that were driving the
project schedule. Fantastic (these tasks are to get my special attention)!
Hmmm... A lot of tasks scheduled to be done in parallel though......

Problem is, that we are not a institution with unlimited resources, and/or
unlimited resource availability. In fact we have a finite number of staff,
each with a variety of skills. NO PROBLEM!! Bring out the resource leveling.
Set it all up properly (priorities, etc.) and hit the level button!

Ta-DA!! Not perfect, but now we have a somewhat leveled schedule with a new
finish date. Truth is, up to this point, I don't think I am doing anything
out of the ordinary with the software, and I would expect many PM's are doing
the same up to here.

Now we get into the sticky "definition" of CPM. What I would now like to do
is identify the ...."path of tasks that are driving the schedule". (wink - I
did not call it the critical path). Maybe do something nice - like high light
them red and give each of them a closer look.

Problem is that if you look at the MSP "critical path", many of these tasks
no longer have any effect on the schedule. Can anyone help me with my new...
uhhh... critical "chain"?!?! (I guess people are calling it).

In my opinion, this would be the whole purpose of running a Critical path
analysis, and so the original question... Does anyone know of a simple way to
get MSP to do it?!?! Or am I stuck with going in, idetifying by hand, and
manually highlighting it??!

"still lost babe in the woods"
 
M

Mark E. Read

A company called Spherical Angle has an add-in to Project that does a
good job of doing Critical Chain scheduling.

It turns off calculation and does its own logic. I saw a demo of it a
couple of years back, and worked on it a bit. Very impressive.

I DO think that the project product team should investigate opening up
the scheduling engine to address some alternative methods... but I'm
not holding my breath yet.

--Mark
 
P

paul

Trevor said:
And I really wanted that "resource leveled critical path", and thought that
not having it was a defect in the CPM or the tools.
It turns out that it is not really all that necessary.

Respectfully, I disagree with that. The critical path shows which
tasks on which to focus attention (to ensure timely completion) or to
potentially shorten if possible. The same desires hold when in a
resource-constrained situation.

I realize that the "critical path" is defined solely by the task
dependency network, but the common understanding, as Trevor pointed
out, is that it's the "path of tasks that are driving the schedule".
From that standpoint, I want a big red line of cascading tasks
highlighted, regardless of whether it's a task constraint or a
resource constraint. It *is* a shortcoming of the tool, IMO, that one
is forced to identify the resource critical path manually.

Paul
 
P

paul.burton

Hey Trevor - thanks for the speedy reply......

Please don't intrepret this as being confrontational, but let me try to
explain what I am trying to do, and why I was hoping the CPM feature in the
software could do what I was hoping to do...

I have started with a work breakdown structure for the entire project, and
then proceeded to put in all of the "hard links" - tasks that are
neccessarily required as successors or predecessors.

At this stage, I was able to turn on the critical path, and low and behold,
there it was - a line of tasks from start to finish that were driving the
project schedule. Fantastic (these tasks are to get my special attention)!
Hmmm... A lot of tasks scheduled to be done in parallel though......

Problem is, that we are not a institution with unlimited resources, and/or
unlimited resource availability. In fact we have a finite number of staff,
each with a variety of skills. NO PROBLEM!! Bring out the resource leveling.
Set it all up properly (priorities, etc.) and hit the level button!

Ta-DA!! Not perfect, but now we have a somewhat leveled schedule with a new
finish date. Truth is, up to this point, I don't think I am doing anything
out of the ordinary with the software, and I would expect many PM's are doing
the same up to here.

Now we get into the sticky "definition" of CPM. What I would now like to do
is identify the ...."path of tasks that are driving the schedule". (wink - I
did not call it the critical path). Maybe do something nice - like high light
them red and give each of them a closer look.

Problem is that if you look at the MSP "critical path", many of these tasks
no longer have any effect on the schedule. Can anyone help me with my new....
uhhh... critical "chain"?!?! (I guess people are calling it).

In my opinion, this would be the whole purpose of running a Critical path
analysis, and so the original question... Does anyone know of a simple way to
get MSP to do it?!?! Or am I stuck with going in, idetifying by hand, and
manually highlighting it??!

"still lost babe in the woods"

:









- Show quoted text -

Hi,

You can only do this by manually formatting the critical chain bars.
Yuck...but the good thing is that, unlike the critical path, you'll
find the critical chain doesn't change like the critical path does.

Critical chain is based on a statistical theory called "theory of
constraints". It basically tries to focus on the value stream of a
project as defined by the "constraint" on delivering it, ie the
availability of people to do the work. This is often treated as a
controversial idea.

MSP uses the right maths to define the critical path as critical path
method does not take into account the impact of resources. One of my
favourite tricks is making MSP repeatedly deliver a critical path with
free float all over it (sad, I know).

Anyway, I think Advanced Projects (http://www.advanced-projects.com/)
do an MSP add-on to automate critical chain generation, inlcuding the
automation of 50% task times feeding buffers and project buffers. Very
nice, too. And some good books about the theory.

Paul Burton PMP
 
P

paul

Hi,

You can only do this by manually formatting the critical chain bars.
Yuck...but the good thing is that, unlike the critical path, you'll
find the critical chain doesn't change like the critical path does.

Critical chain is based on a statistical theory called "theory of
constraints". It basically tries to focus on the value stream of a
project as defined by the "constraint" on delivering it, ie the
availability of people to do the work. This is often treated as a
controversial idea.

MSP uses the right maths to define the critical path as critical path
method does not take into account the impact of resources. One of my
favourite tricks is making MSP repeatedly deliver a critical path with
free float all over it (sad, I know).

Anyway, I think Advanced Projects (http://www.advanced-projects.com/)
do an MSP add-on to automate critical chain generation, inlcuding the
automation of 50% task times feeding buffers and project buffers. Very
nice, too. And some good books about the theory.

Paul Burton PMP

The manual formatting of bars is not very difficult. "Dynamic
Scheduling with Microsoft Project 2003" suggests creating a view in
which tasks with the Marked field = true are shown in red. Once the
setup is done (about 3 minutes), you can just toggle the Marked field
and the bars turn red. Tracing through several hundred tasks is
fairly easy. There are macros to automate it as well.

Paul
 
P

paul.burton

The manual formatting of bars is not very difficult.  "Dynamic
Scheduling with Microsoft Project 2003" suggests creating a view in
which tasks with the Marked field = true are shown in red.  Once the
setup is done (about 3 minutes), you can just toggle the Marked field
and the bars turn red.  Tracing through several hundred tasks is
fairly easy.  There are macros to automate it as well.

Paul- Hide quoted text -

- Show quoted text -

I like it
 
P

paul

I like it

Since the critical path is often part of the resource-constrained
critical path, it's helpful to show the resource-constrained tasks in
a different color (e.g., light red or purple) than the true critical
tasks. It helps to identify the potential methods for shortening the
schedule. In addition to the ordinary methods of shortening the
critical path (e.g., splitting a critical task between more
resources), you can also free up a resource needed for a resource-
constrained task. In other words, you have another option for this
type of task.

When updating the RCP, the first thing I do is copy the "Critical"
field into the "Marked" field. This allows filtering on Marked to show
the entire chain. Then trace back looking for delays introduced by
lack of resource availability. In the bar setup, put the Marked bars
before (above) the critical bars, so the real critical tasks will
overwrite the Marked color or else put "Marked, not critical" in the
formatting for the marked bars.
 

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