ALAP constraint behavior question

Tom,

you are perfectly right, SF link is only a workaround; it does not answer the fundamental question of the difference between Total Float or Free Float being used in the so called ALAP constraint

I will have a try to your VBA macro

Alexandre

Alexandre,

If your only objective is to manipulate the dates to get what you want, then the reverse logic and SF link may be OK; it seems common enough among MSP users of all experience levels.  It is nonetheless a misguided approach in logic driven planning, in my opinion. 

Equipment must be delivered before it is installed - full stop.  To discard this requirement and insert the SF link as you suggest is to damage the proper logic flow through the schedule.  As a result, the late dates and Slack of activity 2 (delivery) and its predecessors (e.g. specification, PO, design, production, etc.) are incorrect.  Moreover, the correct scheduling (early dates) of activity 3 (installation) and its successors is not assured in case of a delay of the equipment.

Hello Planners,

I would use a Start to Finish link between the activities 3 (Predecessor) and 2 (Successor)

By doing so, the activity 2 would finish at the begining of activity 3, and would not push activity 3 ahead against the milesone

This is the best workaround in MSP, whatever the version you are using .

Alexandre

Hi John,

Wouldn't it be possible, to simply run Activity 2 with a relation type FF to Activity 1? 

Marco,

Thanks for the comment, though I would disagree with your characterization of MSP as a "poor and amateur application."  I would say it's a reasonable scheduling application with some pluses and minuses - primarily aimed at a "poor and amateur", but extremely large, user base.

Rgds, tom  

Hello Tom and John,

Hi John,

The behavior you seek is that of a Zero-Free-Float constraint, which is not available in MSP.  When used in a forward-scheduled project, the ALAP constraint in MSP is in fact a Zero-Total-Float constraint, which serves no useful purpose as you have found.  Though my memory is a bit fuzzy on the earlier versions (and I skipped from Project '98 to Project 2003), I'm pretty sure MSP has never had a ZFF constraint.  The workaround, at least where Task 2 represents a just-in-time delivery, is to insert a readiness milestone between 1 and 3.  Then make that milestone an FF predecessor of 2.  This keeps the logic flow intact without using the C-word.

Zero-Free-Float constraints are certainly available in other scheduling software - P3 actually called it by that name.  P6 calls it ALAP, which of course causes much confusion for P6 user who stumbles into MSP.  I think Asta Power Project allows entire strings of activities to be similarly delayed within available free float - pretty flexible.      

I'm not sure if PP has fixed its image retention problem (uploads like yours were only retained for a couple hours).  If not, I'll move the image below (including the workaround) to an external host. Good luck, tom

[[wysiwyg_imageupload:6094:height=618,width=494]](18Sep'18 - changed image link to external source.)

I'm glad you got it worked out.

Sorry I didn't think to mention that macro, which I don't use much.  Maybe I would use it more if it were improved by combining it with a longest-path-type backward logic tracer.  As it is, I've become less reliant on ZFF constraints over the years - in both MSP and OPV - so it's not worth the time to improve the macro.