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Primary & Secondary Constraints => When ?

8 replies [Last post]
Fri, 2007-12-07 15:58
Patricia Le Clainche
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Hello PPs,
Is there anyone who used both Primary and secondary Constraint in the case of Finish Milestones, that haven’t any predecessor ?

What do you put in Primary and in Secondary ? In which order do you put "Finish On or Before", and "Finish On or After" ?

Are there any other cases (for tasks ?)we could use them without complicating the critical path analysis ?

Best regards.
Patricia
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Replies

Sun, 2007-12-09 04:34
#1
Dieter Wambach
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Hi Patricia and Andrew,
I absolutely agree to Andrew’s post. In addition those dummy activities have some background:
By experience there are contacts with the "subbies", e.g. expediting, meetings, reviews,...and later you can easily trace their performance by planned vs. actual. In negotiations for future projects it might help.
Regards from Germany
Dieter
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Sat, 2007-12-08 23:56
#2
Andrew Dick
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Patricia,
I have previously used finish Milestones with no constraints to provide indicative dates to the subcontractor showing the date our design will be complete thus allowing them to commence their work.

After they have finished their work, we need to know when to be onsite to carry out testing of the equipment that they have just built and installed to our design, so I use a start MS with a start on or after, meaning it will anchor to the date we are given in the subbies forecast. I have also used a ’dummy’ task or placeholder as I cll them to represent the subcontractors activities within the schedule (for display on the GANTT chart only, as management like that)

Generally I like to have a fairly comprehensive list of subcontractor milestones from both us to them and them to us, that way you can get a better idea of where they’re up too, (of course that is predicated on them telling you the truth in their status sheets).

Andy
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Sat, 2007-12-08 06:47
#3
Dieter Wambach
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Patricia
At least you have the order to the subcontractor. We might received drawings as well. Subcontractor’s ms often are predecessors to internal activities.. They are not isolated from your project.
Salut
Dieter
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Sat, 2007-12-08 06:32
#4
Patricia Le Clainche
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Hi Andrew, Hallo Dieter,

I agree with both of you, a finish milestone has minimum one predecessor in general cases.
But I have sometimes the case of main sub-contractors milestones that we just want to follow in our internal project. In that case we do not have tasks. And to shw an enetual delay of the sub-contractor, I try to use both constraints. And, what should I do, putting the target date in Primary (finsh on or before) and the forecasted date in Secondary, or the opposite ?

Grüss / Kindest regards.
Patricia
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Sat, 2007-12-08 06:24
#5
Dieter Wambach
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Hi Andrew
I follow the principle of a closed schedule as well. So all finish ms have a successor (same way as you do it) and vice versa for start ms.
In addition: The only sense to distinguish bewteen start and finish ms I see for filtering especially for management overviews.
Regards
Dieter
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Sat, 2007-12-08 06:16
#6
Andrew Dick
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Touché Dieter,
The theory of the closed schedule does require that all activities/milstones/etc have a predecessor and successor, save for the start and finish nodes of the schedule.

To this end, I generally complete all of my finish milestones to an extra little MS caled a ’Tie off’ MS. This little fellow has as it predecessors ALL (save one) of the finish milestones in the schedule and it’s one and only successor is the final end milestone of the entire schedule.

Some may argue that this seems a little odd, however it is of immense help when looking for dangles in the schedule created from adding or deleting activities. Also the use of the tie off milestone is needed in my schedules as I do not run logic through milestones, I.E. Milestones as you put it "They indicate the end of a group of activities" and therefore as I see it no discrete activities should succeed a finish milestone.

On the other hand Start Milestones have the same problem in reverse, and as such any Start Milestone is simply linked to have a single predecessor of the project ’Start Miletone’ with sucessor logic of the discrete activities associated with the deliverable.

So there you have it a 2 minute explination of how I use milestones.

Andy
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Sat, 2007-12-08 06:02
#7
Dieter Wambach
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Salut Patricia
Basically I agree to what Andrew said.
Just one remark for how to use finish ms:
They indicate the end of a group of activities. They always should have predecessors.
As far as I know there’s just one possible combination of two constraints: "As late as possible" together with "Finish on or before" - seldom, but might happen in real life.
Bonne journée / Have a nice day

Dieter
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Sat, 2007-12-08 05:26
#8
Andrew Dick
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Patricia,
It has always been my preference to NEVER use Hard Constraints (Fixed dates), However when it comes to soft constraints such as you have mentioned them, I use those for customer, subcontractor input/deliverable items, such as plans, Technical data, or subcontractor products.

I have used Start milestones for these and placed a ’Start on or after’ constraint on the milestone. That way the remainder of the schedule post data/deliverable milestone can hinge off that date. As soon as there is any update regarding the expected acheivement date of the milestone, it is updated in the statused program accordingly.

There are pros and cons for this approach as I have encountered isues with constraints placed on project finish milestones, NOTE - It is my personal preference not to use a constraint on any finish milestone, as I prefer the schedule calculations to run un-impeeded, therefore only the dates that I MUST constrain are constrained.

Andy’s two cents

Andy
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