A brief history of Scheduling

Samer,



Black Box is not knowing true float after resource leveling, even on a two activities schedule Primavera (all versions), Microsoft and Asta gives you the wrong answer.



Proposing not using resource leveling functionality on thousands of activities is kind of insane.



I agree with you with regard to any software that give you wrong float after resource leveling, better do it at the 1950’s way, by hand as the 1960’s is still wrong, and worst, is misleading.



Best regards,

Rafael

Dear Samer,

CPM schedules will be the same if the original data are the same and the software the same way interpret these data.

For an example, ALAP activity means different for MS Project and P6 (and Spider).

But everything changes if resources are restricted. CPM does not work anymore and the levelling results that are produced by different software are not the same.

We are proud thatSpider Project calculates the best (shortest) resource constrained schedules.

Please inform me about the software that you use and I will send you the examples.

Best Regards,

Vladimir

Samer,



For a start different software use different resource leveling algorithms, even in Spider Project you have the option of several algorithms, a truth not to shame not to hide, on the contrary to be openly exposed.



There is also another difference in computation of Early Start where this value is dragged to the right in most PDM computations but that can be modeled to be at the left under PDM computations, this is solved by P3 when you allow for activity splitting. I believe it can be better modeled under PDM without activity splitting and just to specify if drag to left or drag to right. The remaining is mathematical computations based on the different types of float. I would like it to be available not at the project level but at the activity level.



On the issue on continuous/discontinuous (non-split/split activities) the following article can serve as a start.



http://www.pmicos.org/topics/aug2006tom.pdf



As Vladimir once said AOA and PDM are just different representations of the same.



Best regards,

Rafael

If you still do not see the resource dependences you can add some milk by selecting Create Dependences. Thes will be shown in the Gantt diagram as dotted lines. Once again, remember these are dependences that can change as the schedule is updated and time demand for resources changes. These are not fixed and in any way will interfere with true resource leveling.







Best regards,

Rafael

MILK TO THE OTHER SOFTWARE AS IN SPIDER PROJECT YOU GET TRUE FLOAT

AFTER RESOURCE LEVELING.

Hi Rafael



Did you know that the Gene Kelly clip should really be called - Singin’ in the Milk.



Plain water didn’t show up on the film so they added milk to it.



The actual song was first performed back in 1926.



Best regards



Mike Testro

Mike,



You can have a thousand activities delayed by resource constraining and none critical. That resource leveling delayed an activity does not means the activity became critical.



But just imagine my two activities schedule and adding a third activity not tied to any other, not requiring any resource and with 20 days duration. After resource leveling one of the remaining two activities will be delayed but none of these two will be critical, of course most software will still show wrong float for these activities.



Best regards,

Rafael


Vezi mai multe video din Muzica

PS. Mike if you have not seen the movie Green Zone you will find another impersonator of a PP member.

Hi Rafael



In Powerproject if you have set up a resource leveling operation - which is very rarely in my case - on each reschedule a note comes up which tells you which of the levelled tasks have not been moved and have therefore affected the critical path.



Not as good as Spider I agree.



Best regards



Mike Testro



PS I’m gonna kill that pesky Gene Kelly impersonator.

Sammer,



As to keep it simple limit the schedule to 2 activities, a single resource and a single calendar, it still will be wrong. The wrong output from SureTrak was as per 2 activities, a single resource and a single calendar.



Another way to find out the computations are wrong is if some activities are missing is by filtering for critical activities and if you see a discontinuous path most probably the cheap software left some out because is calculating wrong float for resource critical tasks.



Meanwhile to make it easier I will look for a single activity sample job where the single activity is not critical, of course without setting a job finish constraint or any other dirty trick to bypass computations.



Best regards,

Rafael

The following illustrates how wrong the computations for float on a simple 2 activities job can be.







Best regards,

Rafael

Samer,



I believe in P6 you can schedle an activity without the use of steps, this is a functionality with other purposes, but I am not a P6 user.



If you have P6 you can try with the following monstruous 2 activities job.



Schedule a 2 activities network, not tied one to each other by precedence logic but sharing a limited resource.



For example:



Activity A – 5 days

Activity B - 5 days

Both activities claiming for Resource A of which only one is availble.



Most software under resource leveling will schedule A and B at different time, the first one depending on your priorities selection. This is ok up to this point, but the problem is most will show float of 5 days on the first activity while a delay in this activity will delay the completion of your schedule.



Imagine that you as a Project Manager look at the available float as per your CPM schedule and start paying attention to those shown as critical and even start moving resources from those showing some float as to keep under control those showing no float. Because most software under resource constrained schedule will show the wrong float for resource critical activities you most probably will end up moving resources precisely from the wrong activities. You either will discover too late it was wrong or start doubting about the CPM float display. Well better start doubting about the CPM float display and either buy a glass ball or software capable of showing resource critical float.



You got to know what is driving your schedule in order to take control.



Best regards,

Rafael

Thank you, Samer,

the paper is interesting and I found it on another site http://www.mosaicprojects.com.au/PDF_Papers/P042_History%20of%20Schedui….

It is interesting that Russian joint venture of ICL (ICL-KPO) is one of our Russian distributors.



Rafael,

Spider Project calculates Resource Critical Path and true resource constrained floats since 1993 when it appeared on the market. In 1996 I had made presentations at IPMA Congress in Paris and PMI Conference in Boston speaking about Resource Critical Path and paying special attention to the wrong total floats calculated by known software packages when resources are constrained. Since then nothing had changed except the invention of Critical Chain (other name of Resource Critical Path).



There is a lot to write about resource constrained scheduling but I expect that Patrick decided to make very brief guide.

I believe that an author of this paper is PP member.



Best Regards,

Vladimir

http://www.pmforum.org/library/papers/2006/A_Brief_History_of_Schedulin…



- "Conclusions

The evolution of scheduling has been a fascinating journey:

• Kelley and Walker set out to solve the time-cost conundrum and invented CPM. For most organizations the resolution of time-cost issues is still in the ‘too hard’ basket (although

SPIDER offers an interesting solution)!"



There is no mention as to the fact that few software, if any, other than Spider can provide you with true Float after resource constraining. This has been known for decades at the college level thesis but not at a practical software application until now.



Maybe the article was written before this functionality was available in Spider.



Best regards,

Rafael

Hi Samer,



Sorry, I can’t, but if you are going to ask me about another "spider" - Spider Solitaire, then I would say that I’m an expert.



Regards