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Scheduled Early Start vs Calculated Early Start

2 replies [Last post]
Sat, 2008-06-07 07:22
JN Brown
User offline. Last seen 13 years 11 weeks ago. Offline
Joined: 8 Dec 2007
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Hello all,

I’ve seen the following expression on a web site related to Project 2007 for the definition of FNET constraint:
-----------------------------------------------------------
(Scheduled)ES=(Calculated)ES + Delay
Finish No Earlier Than: Schedules the task to finish on or after the constraint date.
-----------------------------------------------------------

FNET concept is very clear to me but I didn’t get what
s/he meant by this expression.

I believe there is no "scheduled early start" concept. It
is also calculated by Project by using CPM on the background, Is it correct ? You don’t schedule early
start, it is calculated.

That’s the URL: http://ossmall.info/2008/01/17/definition-of-microsoft-project-constraints/

I am OK with this one: for MSO it says EF,LF,SF=CD. MSO means zero slack so EF=LF and scheduled finish (SF). I guess SF is what we see on the Finish Date task field.

Thank you for any feedback, I really appreciate it.

Best Regards.
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Replies

Mon, 2008-06-09 23:17
#1
JN Brown
User offline. Last seen 13 years 11 weeks ago. Offline
Joined: 8 Dec 2007
Posts: 8
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Thank you Darren for your reply, I really appreciate it.

It is pretty clear now.

Indeed, I was looking for some information on how MSP calculates (I guess it’s CPM on the background) [Early/Late]-[Start/Finish] Dates if there are Constraints and Deadlines defined for the tasks on the network diagram and I came across "ossmall.info" web site after some googling.

Thanks again.

Best Regards.
JNB
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Mon, 2008-06-09 10:23
#2
Darren Kosa
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Joined: 8 Feb 2008
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Hi JN,

This probably isn’t the best depiction of task constraints I’ve seen, but by no means is it the worst. I would probably have gone one step further and grouped them under Flexible, Hard and Soft headings to further deconstruct the constraint types.

Some of the acronyms are confusing, ES / EF / LS / LF are fine as they relate to network diagramming and forward / backward passes, but using SS and SF to represent start and finish dates when they’re also used by MS Project to describe task linkage is probably not what you would call ‘best practice’ guidance.

I would have also looked at it from the view of Start / Finish dates (planned or scheduled – what ever definition you want to use for Start / Finish), rather than ES or EF.

Ignoring the slightly over complicated formulae for SNET / SNLT / FNET / FNLT, ALAP and ASAP are clearly wrong (but the examples are from an unsubstantiated source on the internet so what would you expect). I would suggest the following:

ALAP
Instead of ES=(Calculated)LS, it should be...
Start date = LS (ES would not equal LS, calculated or otherwise, if there is free float or free slack as described by MS Project)

ASAP
Instead of (Scheduled)ES=(Calculated)ES + Delay, it should be...
Start date = ES (scheduled and calculated ES, the terms are confusing, there is only one ES with or without the addition of a delay)

Of course this all falls apart if you don’t have the ‘Tasks will always honor their constraint dates’ checkbox ticked!! ;)

Regards,

Darren
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