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Subtle problem with end constraints Thread Tools Search this Thread Display Modes
The very last item in my plan is scheduled As Late As Possible and has an end constraint. All other things being equal I would expect it to be scheduled so it finishes at it's end constraint time.

Yet when I level the resources it gets rescheduled to several days earlier than it's end constraint for some reason I can't fathom.

However if I add an unrelated milestone to the project at some point in the future beyond the end constraint time above and level, my task is rescheduled to end at it's end constraint time - as I would expect.

This only occurs to the task that is furthest in the future in my project.

Have I misunderstood something?

(Using V2.0.3)

Last edited by psidnell; 2012-04-27 at 11:29 AM..
 
OK - quicker example.

Create a new project with one task.

Set an end constraint on that task of several days into the future, schedule it As Late As Possible and level.

It seems to stay where it is, as if it were scheduled As Soon As Possible.

Add a second task beyond the first and level.

The first task moves to finish on it's end constraint time.

Remove the second task and level.

The first tasks shifts back.

Is this correct?

Last edited by psidnell; 2012-04-27 at 11:29 AM..
 
I don't know if it is correct, but it fails the "I could explain this to my mother" test!

It looks to me like that constraint needs something to "push against". If I create a milestone and set its start/finish date to the date I was using as the end constraint, everything appears to work as I would expect. The ALAP task gets shoved back against the milestone, if I put a dependent task on the ALAP task, that gets shoved against the milestone with the ALAP task as close as possible, etc. Without some other task to push against, it looks like the ALAP task will be scheduled ASAP. To me, that sounds like someone missed a case, but maybe it is intentional.

(I was testing with 2.1.2 sneaky peek r166098, just in case it matters)
 
Thanks.

I've solved the problem by leaving a dangling EndOfTheWorld milestone at the end of my project, guess I'll be leaving there then.
 
I've filed a bug report for the issue.

I have a project (my Son's not inconsiderable homework diary) that OP is the ideal tool for.

What I was doing:

For each item of homework I'd have a milestone representing when it must be handed in. To that I'd wire a work task scheduled ALAP (of course!). This worked fine but meant two tasks (the work and the milestone) for each piece of homework and some wiring to do. A little too much data entry work for my liking.

What I want to do:

Simply have a single task for each piece of homework where the due date is the end constraint for each task. Then there'd be only one task to enter per piece of HW, no wiring and the plan would be easier to read.

I did discover that it's not just the last task that's affected by the issue, it can cause other problems that disappear if tasks are needlessly wired together.

Quote:
Originally Posted by whpalmer4 View Post
It looks to me like that constraint needs something to "push against".
It certainly looks that way.

I guess, this is probably a mode of use people don't use much - tasks a usually wired together with a milestone at the end.
 
Boiled it down to this (which actually has no constraints it's the ALAP that's the issue I think):

This is a new project (using 2.1.1.) Add two tasks using Resource 1 and a milestone then wire it up thus:



Task 1 and Task 2 are scheduled ASAP by default, all is good, no violations.

Flip Task 1 & Task 2 to ALAP and:



I would have expected that both tasks would have shifted to the right a little, but not that they would overlap and conflict.

By adding a dependency from Task 1 to Task 2 the problem goes away:

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Last edited by psidnell; 2012-04-28 at 04:47 AM..
 
AHA! user error.

Discovered the project setting "Direction" to "Backwards from fixed end" makes it do exactly what I want.

I hadn't realised there were global scheduling engine settings.
 
I knew about global setting, and I still think I can demonstrate counter-intuitive and/or broken behavior.

Create a single task, set to be scheduled ALAP. Set an end constraint on it sometime in the future. Level. Where is the task scheduled? Change the project's scheduling direction. Level. Does the task move?

Create an ASAP plan with two identical tasks. Set both tasks to be scheduled ALAP. Assign both tasks to Resource 1. Level. You should get a violation about couldn't fit task during resource leveling. Why? It knows how to handle the same case with ASAP scheduling. Same error occurs if done with an ALAP plan and ASAP scheduling of the tasks. The violation window also reports "Task 1 has an end constraint date of " (but no date). Does that seem like the intended result to you? :-)
 
Quote:
Originally Posted by whpalmer4 View Post
Does that seem like the intended result to you? :-)
Well, it's certainly non-optimal :-)

Clearly there are several scenarios above where there is an obvious violation free solution that the scheduling engine isn't finding, whatever the settings.

If my son did his homework ASAP rather than ALAP I never would have noticed :-)
 
Quote:
Originally Posted by whpalmer4 View Post
I knew about global setting, and I still think I can demonstrate counter-intuitive and/or broken behavior.

Create a single task, set to be scheduled ALAP. Set an end constraint on it sometime in the future. Level. Where is the task scheduled? Change the project's scheduling direction. Level. Does the task move?

Create an ASAP plan with two identical tasks. Set both tasks to be scheduled ALAP. Assign both tasks to Resource 1. Level. You should get a violation about couldn't fit task during resource leveling. Why? It knows how to handle the same case with ASAP scheduling. Same error occurs if done with an ALAP plan and ASAP scheduling of the tasks. The violation window also reports "Task 1 has an end constraint date of " (but no date). Does that seem like the intended result to you? :-)
Hi there, I've just discovered this issue/occurrence as well, and am rather perplexed by it. But it seems that you understand it and/or why omni plan is doing it. I was wondering if you'd be able to elaborate a little more as to why omni plan causes this scheduling conflict? I'm just trying to wrap my brain around why it chooses to cause a violation of the tasks. I know this thread is a little old now, but if you're able to try and explain it any more, i'd really appreciate it. Thanks! (Or is this actually a bug?)
 
 


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