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multiple critical path

24 replies [Last post]
Mon, 2010-02-01 11:52
Rola Sabbah
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hi
i was wondering how can we develop more than one critical path in P6 ? is it a good practise?
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Replies

Thu, 2010-02-04 20:30
#1
Rafael Davila
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Andrew,

10-4
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Thu, 2010-02-04 20:22
#2
Rafael Davila
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Mike,

Same as you I follow my principles, even when I have no money reserves. It is the right thing to do, is the only way I can sleep at night. I believe in the honor system but in no way naive. I bark but do not bite.

Because of our debates, long ago I know you stand by your principles and enjoy debating with you, as always I am looking for our next match.

On guard!

Best regards,
Rafael

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Thu, 2010-02-04 20:05
#3
Andrew Trainor
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Thanks for you help, Raf, you were right in saying I wanted to show the true CPM logic.

I removed the link to the contractual milestone and put a constraint for it and is now showing the logic of the construction works.

Sorry if the description was unclear. Thank you for the responses.

Andy
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Thu, 2010-02-04 19:50
#4
Rafael Davila
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Andre,

I am a Spider Project user, my personal choice, but as everyone I have particular interest in MS Project as is the most widely used scheduling software so I might be breaking some basic good practice rules of MS Project, my excuses in advance.

I understood you want to know how to keep true CPM logic in MS Project and still show your contractual milestones. Let me know if I am wrong.

It can be done in several ways but the following is what I would do, subject to the critic of everyone as this is a place to search true knowledge.

MS true CPM logic

Key issues:

1- I used the option for multiple critical paths.
2- The contractual Milestones have no logic predecessor/successors and are fixed through a must start constraint, each is an open end.
3- All network activities with the exception of the milestones share a single start and finish event in accordance to good practice.
4- Notwithstanding the above only individual milestones and one network are open ends. Therefore you will get true critical computation on the network as per the rules of good practice for CPM.
5- Avoid any type of finish constraint.
6- Avoid any type of “must start/finish” constraints except for isolated reference milestones, logic should drive all activities. Again only isolated milestones should be frozen with “must” constraints.

Best regards,
Rafael
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Thu, 2010-02-04 18:37
#5
Trevor Rabey
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Andrew,
You are going to have to re-write your question and describe the situation more clearly because it is indecipherable as it is. Or maybe it’s just me, but I cannot figure out what the problem is.
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Thu, 2010-02-04 18:18
#6
Mike Testro
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Hi Andrew - welcome to PP.

Lets see if I have got this right.

You are submitting a tender which has an expiry / acceptance date of 3 months after submission.

The fit out works are required to finish 2.5 months after commencement.

What is the commencement date of the works?

Does cpmmencement have any relationship to the tender expiry date?

Best regards

Mike Testro.
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Thu, 2010-02-04 16:36
#7
Andrew Trainor
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Hi - (Its my first time post)

I am using Ms Project, but question relates to the current conversation.

I am currently working on a tender fit-out programme with a milestone for our Tender Expires 3 months after the submission.

The client requires the completion of works after 2 and 1/2 months. Meeting the client’s completion date (without including the constraint dates) I know have once activity on the critical path after the tender submission - the tender expiry date.

Is there a way I can show the critical path of the works as the tender expire date is just a milestone at the end of the project (although important to include, not affecting any works etc), without using a constraint on the PC date?

Thanks

Andy
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Thu, 2010-02-04 16:10
#8
Mike Testro
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Hi Rafael

You are right in all respects.

Now do you follow your principles or the money.

I am fortunate in that I have enough reserves to be able to follow my principles and tell the shysters to piss off.

Best regards

Mike Testro
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Thu, 2010-02-04 07:06
#9
Rafael Davila
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This mean that by definition in the USA most Owners following the PMI "Good Practice" to use negative float are fraudulent to the Contractor when the software they specify cannot provide you with true CPM computations unless you delete the artificial "end on or before" constraints.

I agree with the view of most UK Schedulers that oppose using such functionality. Perhaps our PMI is biased, I understand one or a few of their founders were previous Primavera employees, maybe still receiving a monthly retirement check from Primavera. It is not a free "think tank" as we would like it to be.
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Thu, 2010-02-04 03:16
#10
Mike Testro
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Hi Rafael

In some jurisdictions "fooling the logic" would be fraudulent.

Best regards

Mike Testro
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Wed, 2010-02-03 16:23
#11
Rafael Davila
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Mike,

Seems you are very lucky, unfortunately at home we are required by contract to fool true critical path with functionalities such as the infamous constraints that create negative float.

Even the PMI calls it "Good Practice", so we are stuck with rubbish software that in order to get true critical path metrics you have no other option than delete your constraints to understand logic, a Global Change can help here. Then if doing a recovery schedule you must restore your deletions one by one with the correct date for all constraints you deleted, here a global change won’t be enough.

With the help of formulas you can tame the issue, but not all software provides this functionality.

Now I am using software that best fits my needs, that do not allows you to fool scheduling logic but stuck with Owners that are still insisting on the PMI “Good Practice Recommendation” to fool logic with the creation of negative float using finish constraints. What a mess, this you cannot solve with simple formulas, you got to fool backward computations even if not taking into account resource constraining. To the lions with the PMI.

Best regards,
Rafael
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Wed, 2010-02-03 16:18
#12
Samer Zawaydeh
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Hi,

If you do not look at the negative float, how do you differentiate from a critical activity and a very critical activity?

With kind regards,

Samer
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Wed, 2010-02-03 15:23
#13
Mike Testro
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Hi Rafael

It is said that bullshit baffles brains but in my experience bullshit can’t baffle a better bovine scatalogist.

I was brought up on this stuff and I know more tricks on how to create a false critical path than most street fighters in the delay analysis profession.

For instance in PowerProject - select any task on the critical path and set its end time to one second shorter than programmed - the critical path has changed.

When you add different calendars and resources the possibilities are endless.

Change one task to a hammock and leave it showing critical.

And so on.

The first thing I do when encountering a contractor’s programme is spend an hour or two stripping out all the rubbish to get to the true critical path.

And I have never yet encountered a true multiple critical path.

Best regards

Mike Testro.
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Wed, 2010-02-03 15:09
#14
Rafael Davila
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Mike,

Look by setting a finish constraint equal to early finish in all activities everything becomes critical under rubbish software that allows you to fool CPM computations. I even wonder why some activities display free float when total float is zero.

All Critical

Can you tell me how many Critical paths there are?

At home we call it bar-charting. No wonder at the well known meeting of “four CPM gurus” having a few drinks at a pub could not figure it out, and believe will ever be able to do so with software that allows for such a thing. Three of them where right about how bad Primavera is.

Best regards,
Rafael

P.S. Sorry I did not used Spider Project but it does not allow for such a thing.
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Tue, 2010-02-02 15:38
#15
Rafael Davila
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Mike,

To wisely fool not only a few float computations but all. Yes you can fool each and every float computation. Why just the Owner? You can be as wise.

Don’t sell yourself for cheap, if going to get caught let it be for a lot. Submit your initial schedule not with a few aberrations but with a lot of them.

Hey I agree 100% with you.

One of these days we should debate about Start vs. Finish Constraints. I happen to believe into the validity of some start constraints that fix early start of an activity but not its finish, finish is kind of unpredictable, is backward thinking, and should always be left open for CPM computations. Finish constraints functionality should provide only for comparison metrics.

Once I asked Vladimir why Spider does not calculate negative float, he answered me once and never had we talked back about it, no need to. Maybe someday he will provide equivalent metrics; I doubt I will use it, no doubt a few Owners will.

Best regards,
Rafael
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Tue, 2010-02-02 15:22
#16
Mike Testro
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Hi Rafael

You wrote "If on purpose you wisely set a finish no later than constraint on some activities you can make every activity to show 0 total float under such functionality."

What is the wisdom in setting an artificial finish constraint that will overide the programme logic?

You can only generate more than one critical path if you have fiddled with it.

Don’t do it - Never Ever.

Best regards

Mike Testro
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Tue, 2010-02-02 14:15
#17
Rafael Davila
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Samer,

I need to follow the logic, I need the true CPM/PDM computations. I don’t need such an aberration as negative float, in any case "Longest Path" taking into consideration my resource constraints. There is even a longest path to each and every activity on the network and not merely contractual milestones.

Why not to teach Owners how to interpret true CPM logic instead of forcing the contractor to miss true CPM logic. Morons that cannot see the project is falling behind just by looking at the projected milestone dates. Is ironic we Contractors are asked to follow CPM logic when convenient to the Owner and forget about it when is not at the Owner’s convenience.

Software that provides for negative float, without allowing you to switch to true CPM Logic are self serving to the interest of Owners at the expense of the Contractor needs. The PMI by promoting use of such constraints is in part to blame for the lack of a functionality that gives back the contractor true CPM logic.

Best regards,
Rafael
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Tue, 2010-02-02 13:50
#18
Samer Zawaydeh
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Dear Rafael,

When you have delays, then you might more than one path with all the activities on them with zero or negative float. It happens, it does not mean it is meaningless. It means that you most probably have considerable delays on a lot of activities.

You might end up with requesting a revised Program of Works.

With kind regards,

Samer
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Tue, 2010-02-02 13:40
#19
Rafael Davila
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Beware of functionality that redefines your backward pass computations based on a fixed constraint rather than using the computed dates from CPM/PDM logic.

If on purpose you wisely set a finish no later than constraint on some activities you can make every activity to show 0 total float under such functionality. To define multiple critical paths is ambiguous, makes no sense. Then why have Critical Path if it can be anything you want it to be?

Project Critical Path is the longest schedule network path from the project start date or the current project data date to the project finish date, and that is. Anything else should be defined under different name. This rule out the possibility to define open ends as critical. Using the term “critical path” as to mean the longest path from the start date or the current project data date to a particular activity other than the project finish is wrong, the PMI is wrong.

Unfortunately some people miss the fact that “links” are also part of your critical path, under PDM you might have two links between two activities; it might happen that one link is part of the critical path while the other is not. A constraint, and not necessarily a particular/single activity might also be such a “link”, even if temporary.

Best regards,
Rafael
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Tue, 2010-02-02 12:32
#20
Shah. HB
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Hi to all

I have experianced two crtitcal path in a schedule which consists of few activities and two critical paths are in parallel as the activities are linked in parallel path
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Tue, 2010-02-02 11:50
#21
Vladimir Liberzon
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Multiple Critical Paths mean several activity sequences with the same duration, it happens but rarely.
But Critical Path may change during the execution if delays happen on sub-critical activities and this is not rare.
Resource Critical Path may change if there are changes in the project resource pool.
Changes in activity and resource calendars may also lead to new Critical Path.
Best Regards,
Vladimir
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Tue, 2010-02-02 11:29
#22
Mike Testro
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Hi Samer

If there is one critical path in the original contract programme it is unlikely that more than 1 will emerge as the project is updated.

Best regards

Mike Testro
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Tue, 2010-02-02 10:26
#23
Samer Zawaydeh
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Dear Mike,

You can have have more than one critical path. If you have delays on the project, and the float gets reduced, ultimately, the complete project will be critical and red if no work proceeds.

At the start of the project, the sequence and logic are great and you have 1 critical path. But with time, delays happen and the float gets reduced. So you might have more than one critical path.

With kind regards,

Samer
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Tue, 2010-02-02 02:53
#24
Mike Testro
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Hi Rola

No Never - even on P6.

It will mean you have fiddled with the natural logic to create a false programme.

I have never yet seen a properly drawn up programme with more than 1 critical path.

Best regards

Mike Testro
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