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Deadline vs. date constraints question RRS feed

  • Question

  • Hi,

    I'm breaking my head over this one. In my effort to make my planning as dynamic as possible, I used deadlines for tasks instead of date constraints. All tasks are on finish ASAP. Say I have this situation:

    • 20 tasks, all with different deadline dates
    • only 2 or 3 resources assigned to the tasks, never more than 1 on each task
    • work/duration also varies
    • all the same priority

    Now when I level the tasks, some of them go past their deadline date. I understand why. MS P doesn't account for the deadline dates and only gives a visual indicator when going beyond the deadline date. With leveling order set to priority/standard when leveling MS P looks for priority first. They all have the same priority. Next are constraints. They don't have any constraints. Next up is slack which is varying, so leveling is based on slack only. I can see that tasks can be leveled in a way that not a single task goes past it's deadline.  I know I can't make MS P level this way, or the way I want. Another way would be to work with 'Finish no later than' constraint. Since I read many articles about this all stating that avoiding this kind of restrictions is your best bet to level without errors or MS P crashing, I'm in doubt wether to use them or not. What's your opinion on this one?

    Tuesday, January 13, 2015 7:10 AM

Answers

  • Hello,

    You stumbled on a weakness in Project's calculation, namely thet deadlines cannot increase slack, only decrease. In that way, in your project, deadlines simply do not play a part in the calculation, and tasks 5 and 10 are critical - hene the curious result of leveling.

    If somehow you force the project's end to after March 9 (by adding a very long task or a Must constrained milestone f.i.) Leveling gives the same result as linking the tasks because the slack values now take the deadlines into account.

    Greetings,

    • Marked as answer by Peperbusse Tuesday, January 13, 2015 9:19 AM
    Tuesday, January 13, 2015 8:54 AM
    Moderator

All replies

  • First of all, deadlines do not just put a pretty green arrow on the Gantt chart, and flag up a warning when the finish date is later than the deadline. It also changes the way the total slack is calculated, so that when a task finishes later than the deadline it will have negative total slack and will therefore be defined as critical (where the definition of critical is less than or equal to 0).

    What MSP is trying to tell you is that the way you have built your model, based on what you want rather than what you can have, leads to a project plan which is not feasible, or even plausible. You just don't have enough resources to meet the dates you want given the priorities you have assigned.

    What can you do about it? Well the first thing to do is accept what the model is telling you. Denial is not just a river in Africa. The next thing you can do is relax some constraints in order to get a project which is at least feasible. Don't worry if it is not yet optimal. Which constraint to relax? Well, start with the ones which are most arbitrary, probably the deadlines and/or the priorities. If you then level and find out that the tasks finish later than you would like, then you need to swap out some of the over-allocated resources.

    Do not impose any FNLT date constraints. It will just make it worse.

    That's as good as I can do without seeing it. You have my email address.

    Tuesday, January 13, 2015 7:43 AM
  • Hi Trevor,

    Thanks for your feedback. I was doubting myself after reading your reply so I tried a very simple set of tasks with deadlines. Like this:

    Task    Deadline  Duration  Work     Resource

      1       1-14-15   1d             8h       1
      2       1-19-15   2d           16h       1 
      3       1-23-15   3d           24h       1 
      4       1-30-15   4d           32h       1 
      5       2-09-15   5d           40h       1 
      6       2-11-15   1d             8h       1 
      7       2-16-15   2d           16h       1 
      8       2-20-15   3d           24h       1 
      9       2-27-15   4d           32h       1 
    10       3-09-15   5d           40h       1 

    Please try in MS P and let me know what it comes up with. The deadlines give plenty of room to finish the tasks in time with just one resource. But after leveling, tasks 2, 3, 4, 6, 7 and 8 all go past their deadline. When I make a predecessor of every previous task (linking them) the work finishes on 2-23-15 with no overallocation, far before the latest deadline which is 3-09-15. I don't want to make constraints if there in reality isn't any, so made the predecessors just to prove that is possible to level in a way that there isn't any overallocation and all tasks finish on time.


    • Edited by Peperbusse Tuesday, January 13, 2015 8:26 AM
    Tuesday, January 13, 2015 8:24 AM
  • Hello,

    You stumbled on a weakness in Project's calculation, namely thet deadlines cannot increase slack, only decrease. In that way, in your project, deadlines simply do not play a part in the calculation, and tasks 5 and 10 are critical - hene the curious result of leveling.

    If somehow you force the project's end to after March 9 (by adding a very long task or a Must constrained milestone f.i.) Leveling gives the same result as linking the tasks because the slack values now take the deadlines into account.

    Greetings,

    • Marked as answer by Peperbusse Tuesday, January 13, 2015 9:19 AM
    Tuesday, January 13, 2015 8:54 AM
    Moderator
  • Hi Jan,

    Bedankt!! Adding that milestone seems to 'solve' this leveling issue. With these kind of things I find it hard to doubt what the pro's are saying, but I can't neglect what I see. Happy that you could tell what was happening. Do MVP's like yourself have any influence on this kind of things with Microsoft?

    Tuesday, January 13, 2015 9:19 AM
  • Hi,

    Sometimes MVPs are asked about feature suggestions but I never saw much influence. By all means, over the past years there certainly have been nice developments on Project but the scheduling enginehas harly ever been touched.

    Greetings,

    Tuesday, January 13, 2015 1:03 PM
    Moderator