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Date Constraints

16 replies [Last post]
Wed, 2005-01-26 19:28
Bernard Ertl
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I’m aware that P3 offers planners the ability to set (non-mandatory) date constraints on the (ES or EF) and (LS or LF) of any given task. As I understand it:
  • A constraint on the ES means "schedule no earlier than this date". The task may still be scheduled later in time if other relationships take precedence over the constraint date.
  • A constraint on the LF means "intended to finish on this date". The float will be constrained to the target date, but the task may slip beyond that date (causing negative float).
What do constraints on the EF & LS mean? Have you ever used them?

Do you use mandatory constraints instead of non-mandatory ones and if so, why?

Thanks.

Bernard Ertl
eTaskMaker Project Planning Software
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Replies

Mon, 2005-06-13 05:31
#1
Sunil Kumar
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Thanks Jaco that was as simple as that..

Cheers

Sunil
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Sun, 2005-06-12 22:28
#2
Sukumaran Subaram...
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Great Jaco,

Now I can remove all the other constraints effectively without any hassle.

Regards.
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Sun, 2005-06-12 00:17
#3
Jaco Stadler
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Another Methods How to Remove Constraint are

Global
SNE EQ " "
SNL EQ " "
FNE EQ " "
FNL EQ " "
ON EQ " "
MS EQ " "
MF EQ " "

The Nice thing about it once you have it set up you can transfer it for Future USE.

Etc

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Sat, 2005-06-11 12:16
#4
Philip Jonker
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Hi Ganga,

To export relationship, just click on the successors button when you are in the export menu, just remember to give it a file name, for that click on the format button, and remember to save as a dbf file
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Fri, 2005-06-10 01:21
#5
DATTATREYA PADHARTHI
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I normally export the activities in dbf/lotus (all current) & also the relationships.
Delete them from P3.
Delete Fields "ECON", "LCON", "CON", "ECOND", "LCOND", "COND" as may be the case & then export back into P3 (also the relationship file).
This may be useful if you have to delete many constraints else, manually unchecking the Constraints in respective activities is quite effective.

Regards
Dattatreya
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Thu, 2005-06-09 04:42
#6
Sukumaran Subaram...
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Gangha,

You can delete the zero total float and zero free float constraints using global change.

To remove set them to 0; to apply them set them to 1. Eg.:
Then: ZTF EQ 0
Then: ZFF EQ 0

Other type of contraints, you filter the activities with contraint and remove it manually as stated by Philip.

Regards.
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Wed, 2005-06-08 14:56
#7
Philip Jonker
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Hi Gangha,

This is the problem with constraints, the only simplistic method of removing them, is find out where they are and remove them manually.

If anybody out there have found a better solution, pray tell! Give me a go at the database structure, and it will be peanuts, that is why the background like code structures etc, is not accessable in modern day programs
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Sat, 2005-01-29 12:43
#8
Jaco Stadler
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Something that I have forgotten to mention is it is depended on the activity type example.

ES constraint can not be applied to a Finish Milestone you can Only apply EF or LF Constraints.

Same with a Start Milestone.
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Fri, 2005-01-28 04:57
#9
Steven Oliver
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Great care should be exersized when using mandatory type constraints, because as you rightly point out, their use overrides normal logical releationships.

The only occasions where I have been able to use the mandatory constraints was on a project which involved shipping steelwork overseas. In this case the ship was booked and was going to sail on a particular day irrespective of how much steelwork we had ready.

Other examples I have heard are where a date is absolutely immovable i.e the millenium. The millenium celebrations were going to take place irrespective of how many fireworks were ready !.

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Thu, 2005-01-27 16:56
#10
Bernard Ertl
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OK. Thanks everyone.

I’m gathering that the constraints on EF & LS are really equivalent to constraints on the ES & LF - just with the task duration factored in.

From what I can tell, the mandatory constraint hides the impact of schedule delays on all successors to the constrained task. When would using this type of constraint be desirable?

Bernard Ertl
eTaskMaker Project Planning Software
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Thu, 2005-01-27 10:51
#11
Philip Jonker
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Hi Jaco,

Agreed, however, it depends on the type of project, as well as the your scope of work. For turnkey projects your statement probably holds true. A lot of projects are commissioned by the client themselves, and they provide you with a set of commissioning dates required by them to allow them to meet their scheduled start-up date. Unless you link up to their detailed comm schedule, the only way out is to use finish constraints to track the handovers. On the last project I did, a structural steel job, the client required intermediate handover dates, for cladding access, the only way to track these was LF constraints. This was due to the fact that there was some float in the schedule. If you have a better method, I would be glad to hear it, as I don’t like to many artificial constraints in a schedule.

Regards
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Thu, 2005-01-27 09:18
#12
Jaco Stadler
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Hi Philip
Is that not the differance Between Project Planning & Construction / Pre Commisioning Planning

If you have a look at Project Planning you will see that part of a project plan is the start up Schedule this will tel you when you need to Pre Com certain Items.

So it gets back to not enough detail planning in the schedule.

Cheers
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Thu, 2005-01-27 06:09
#13
Philip Jonker
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Hi Jaco,

I agree with most of what you say, however, there is instances where staggered handovers are required (eg. for commissioning purposes), in which instance it will be necessary to have more than one finish constraint to control the float in the logical paths leading to such handovers, that is if you only have one finish in the project.

Regards,

Philip
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Thu, 2005-01-27 05:08
#14
Neeraj Agarkar
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I use EF constraints
1) to mark expected delivery dates as per supplier / subcontractors commitments.
2) to buy more time for certain critical activities which are my responsibility and then put a manadatory finish for my subcontractor’s / supplier’s critical activities to maintain project finish date.
This helps a lot in this part of the world.
I dont know how to use a Late Start?

regards,
neeraj
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Thu, 2005-01-27 02:41
#15
Jaco Stadler
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It is actualy a simple answer it gives you the right to manipilate the "Critical Path" Total Float Calculation. I have only used it when I want to manipilate the Float Calculation.

Why would I like to do that. I dont know some mornings I get up and do strange things. But gerally I use this type of Float Constraint to Build up Hidden Float in the schedule that only I am aware of.

But what it does help with is the the Early and Late Curves of a Schedule.

I can also see some need for it on High Level scheduling were true logic does not apply.

I can also think it can be used for resource Leveling.

Cheers

(Please note I belive in two Constraint per schedule a start/Access and a finsh constraint only)


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Thu, 2005-01-27 02:29
#16
Philip Jonker
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Hi Bernard,

Basically there are early and late constraints, which constrain the early or late dates. The most lögical of the four possibilities is the two you have already mentioned. EF is basically the Earliest Date/time an activity can finish, and LS the latest an activity can start. These sound a bit illogical, but an instance is where you have a certain window in which an activity can or cannot be performed. I personally have not found much use for them. However, there is other constraints available which is is the free and total float constraints, the one I find useful is the free float constraint. Let’s say you have a chain of fabrication activities and another chain of erection activities, and the fabrication of a certain piece of material is complete a month before it is to be erected, but you don’t have storage space on site, you can then insert a delivery activity with a free float constraint, this will move the delivery activity to the latest date it can happen. This means that if the erection activities are ahead of schedule, the delivery activity will move forward, and the opposite when late. When you use the early float constraint, make sure you remove it as soon as the activity is in progress. The total float option I have not found any particular use for.

Lets hear if anybody else have found any useful uses for these constraints.

Regards,

Philip
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