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Critical Path

18 replies [Last post]
Sat, 2009-02-14 07:49
Kamal Al-Hourani
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Could a project be without critical path?
i.e if the project has high float.
i.e if the prject can be done in 1 year and the contract saying two year (for example) does this mean that the project has no critical path as all the activities will be timely relaxed???

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Sat, 2009-02-21 04:52
#1
Abu Lana
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Dear Kamal,
Same as previous answers, like use the longest path as critical, extend durations, re-level the resources... whatever.
but the most important information u mension was, maybe the client need time to finance his project. !!
so what u need is to coordinate with the Client commercial pple and to upload cost as resource, Ex. you add a resource called USD, Euro, GBP or Gold coin... and make it as Driving resource,when scheduling your programme sort the cost histogramme and compare it to the client cash histogramme, It’s like doing the job in reverse.

Hope that it will help you.
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Fri, 2009-02-20 13:17
#2
Samer Zawaydeh
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Hi everyone,

I agree that when things get can get complicated with 5000+ activities. But this is part of the job.

You will need to analyze the information that you are getting from the software to make sure that it makes sense. In other words, debugging.

The best way to do that is to involve the project team and ensure that each part is being represented correctly and the results are also making sense.

After all, at certain point it becomes an art.

Best Regards,

Samer
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Fri, 2009-02-20 11:45
#3
Stephen Devaux
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As I mentioned in the Training forum, my problem with mandating exclusively FS links is that it leads to people doing work in series that could be done partially in parallel. And that can lead to the greatest of all scheduling evils -- longer project schedules that can lead to people suffering and dying unnecessarily.

Don’t get me wrong -- the day that someone who really understands scheduling can get elected World Commander and mandate exclusively FS relationships AND the necessary decomposition to optimize such schedules, I will actively campaign for them. But I fear that that particular cat got out of the station when the train left the bag (so to speak) with IBM’s invention of the complex dependencies in 1964.

The truth is that one can get good (and optimized!) schedules using either format.

1. All FS has the advantage of being clearer and the disadvantage of requiring more work to decompose. That disadvantage often leads (though I agree it shouldn’t HAVE to!) to less parallelism and longer schedules.

2. Complex dependencies have the advantage of being simpler to input and display. They have the disadvantages that:

a. People do them unthinkingly.
b. Users don’t REALLY understand them.
c. PM software programmers ALSO don’t understand them, leading to their arbitrary computations (e.g., reverse critical path, add-on software inconsistencies).

All these things, in both cases, can be fixed with comprehensive training. But since the complex dependency is here to stay, at the very least PM software should handle it properly and schedulers should be adequately trained in ALL aspects of scheduling. (Indeed, I feel that any DRAG calculation method, with or without software, would be totally inadequate if it can’t handle SS, FF and SF, lags and leads, and a host of other creatures of the forest!)

(None of this should be interpreted to mean that I wouldn’t wave my wand to erase the historical development of complex dependencies, if I could.)

Fraternally in PM,

Steve Devaux
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Fri, 2009-02-20 10:56
#4
Darren Kosa
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Hi All,

I’ve not seen any explanation of critical paths or CPM that uses anything other that FS links. Is this just theoretical or is this concept this not practical when applied?

EDIT: Looks like Alistair beat me to the punch!! :o)

Regards,

Darren
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Fri, 2009-02-20 10:45
#5
Alistair Blakey
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This is why Mike advocates only using FS links - everything else messes things up! This is one example; another is risk management software such as Pertmaster which will increase and decrease the durations of activities but not the lags of the links between activities.

Now personally I’m not sure I agree with Mike simply because on complex projects I can see schedules stretching to tens of thousands of activities, making it unfathomable to all but the planner: possibly useful in a retrospecive analysis case but not when the construction work is ongoing.

But in instances such as this where the links create an obviously distorted critical path it is important. As a rule (and I accept that it cannot necessarily hold true in all cases) if there’s a SS link, there should be an accompanying FF link to make sure that there isn’t flawed logic as shown in the example.

Alistair
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Fri, 2009-02-20 09:23
#6
Stephen Devaux
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Samer quoted PMI’s "Practice standard for scheduling":

"The critical path method is a schedule network analysis technique used to determine *the minimum total project duration* and the earliest possible finish date of the project as well as the amount of scheduling flexibility (the amount of float) in the schedule network."

(Emphasis mine.)

I would just like to point out that, under this definition, NO software package’s CPM algorithm, at least that I have ever seen, actually computes the MINIMUM total project duration in certain cases.

The classic example is the "reverse critical path".

A = 6D, No Pred
B = 10D, Pred: A/FS
C = 6D, Preds: A/FS, B/FF
D = 12D, Pred: C/SS2
E = 6D, Preds: C/FS, D/FS

Software algorithms will say that E’s early finish is Day 30. In fact, E’s early finish could be Day 26.

Somehow it seems a shame that, in a 500 or 5,000 activity project to provide clean water, or build a clinic, or inoculate children, or develop a vaccine, lives might be lost due simply to a software algorithm having insufficient intelligence to perform the calculation correctly (i.e., to compute the "minimum total project duration").

Incidentally, there are other problems in this sort of situation: the software will also denote B as being on the critical path (which it isn’t). And if the scheduler attempts to shorten the project by computing DRAG on the CP activities, it will seem as though B has DRAG of 5D, and C has "reverse" DRAG: make C shorter and the project actually gets longer! (In fact, the shortest duration is 22D, A has DRAG = 5D, B = 0D (not on the CP!), C = 2D, D = 4D, and E = 6D.)

I’m going to be speaking at the PMI College of Scheduling Conference in Boston that starts May 17th, and I expect to bring this up. (If anyone here is planning to attend the Conference, please let me know so that I can make time to meet you for a beer -- now THAT’S the importance of good scheduling!)

Fraternally in PM,

Steve Devaux
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Fri, 2009-02-20 02:21
#7
Ben Hall
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Yes Samer, agreed.

That is more or less what I said.

Regards
Ben Hall
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Fri, 2009-02-20 02:01
#8
Samer Zawaydeh
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Dear Everyone,

As per the definition stated in "The Practice standard for scheduling" by PMI

"The critical path method is a schedule network analysis technique used to determine the minimum total project duration and the earliest possible finish date of the project as well as the amount of scheduling flexibility (the amount of float) in the schedule network."

If you are increasing the project duration then your critical path remains as per the definition above, but you have more time to complete the job.

Best Regards,

Samer
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Fri, 2009-02-20 01:53
#9
Ben Hall
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A project cannot be without critical path, "critical" meaning the activities which impact the rest of the linked activities in the project. If the activity is heavily depended on to finish another or multiple activities to start then it becomes critical, regardless of the finish date.

Regards
Ben Hall
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Mon, 2009-02-16 18:56
#10
Stephen Devaux
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"Could a project be without critical path?
i.e if the project has high float.
i.e if the prject can be done in 1 year and the contract saying two year (for example) does this mean that the project has no critical path as all the activities will be timely relaxed???"

Trevor is 100% correct -- a critical path and a contract are unrelated concepts. In the above case, you simply have a lot of schedule reserve at the end of the project. I would try to utilize this by:

1. Getting the client to pay an early delivery incentive.
2. If it’s a fixed price contract, delivering early to reduce "marching army" costs of overhead and LOEs.
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Mon, 2009-02-16 09:16
#11
Kamal Al-Hourani
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as a conclusion in such cases there will be no critical path in front of client.
by the way, we are usually submitting the critical path(s) as part of the updated time schedule report on weekly or monthly basis.
but I agree with the suggestion of optimization between the time and benefits.

Regards,
Kamal
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Mon, 2009-02-16 09:06
#12
Nestor Principe
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I will be tempted to request for instruction to accelerate.

Cheers..
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Sun, 2009-02-15 15:14
#13
Samer Zawaydeh
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Dear Friend,

You need to ask your client to understand why they gave you the extra time.

As a Contractor you need to submit a program to complete the works. You do not have to submit a critical path. If you are allowed to complete the works as soons as possible, then I suggest that you find the best duration with the maximum profit for you and present it as the Program of Works.

Best Regards,

Samer
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Sun, 2009-02-15 08:46
#14
Trevor Rabey
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So you have nothing to fear from being late and LDs, that’s all.
The contract finish date is only the latest date that you are allowed to finish or else, if late, incur LDs.
You still have to perform the project as soon as possible, in order to make money and in order to start another project asap and make more money. Can’t you just finish it and hand it over a year early?
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Sun, 2009-02-15 08:37
#15
Trevor Rabey
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I would suggest that the Critical Path Method has nothing to do with the contract finish date.
The purpose of CPM is to find, among other useful things, the minimum duration of the project, given the durations and predecessors. The CPM could not care less about some arbitrary finish date that someone just made up and wrote in the contract.

The only reason that the contract has a finish date is a "legalistic" one because every contract must have one, for certainty. Lawyers think that they (or the law) are entitled to more certainty than everyone else.

If it takes 10 days to lay 10000 bricks, it is irrelevant whether the contract finish day is tomorrow, next year or 10 years away.
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Sun, 2009-02-15 06:10
#16
Kamal Al-Hourani
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Dear all,
thank you for the reply.
My question is that if a contract is awarded on you with a project time period double the one you usually can perform the project in. maybe because of the client needs or budget or anything else....
and when you want to submit the critical path to the client , it is either you will extend or double every task and relax it or you will assume the longest path is the one even though it is not the critical.

Regards and thanks,
kamal

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Sun, 2009-02-15 00:49
#17
Charleston-Joseph...
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Hi Kamal,

use longest path as the critical path

Cheers
Happy Planning and Scheduling
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Sat, 2009-02-14 11:43
#18
Samer Zawaydeh
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Dear Kamal,

Seems like not a real project. In real projects you need to finish the scope on time and within budget.

If you go to the formula of calculating the CPM and increase the Late Finish for all the activities like you are proposing, then you are delaying you project. That means that you need more resources to stay on the job to complete it.

Best Regards,

Samer
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