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Early Start after Early Finish?

4 replies [Last post]
Mon, 2010-04-12 01:01
Kevin Button
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I’ve been experimenting with a few things in Open Plan and have found that it is possible to set up activity constraints in such a way that I end up with an Early Start date that is later than the Early Finish date.

For example, ’Fixed Target’ finish of 12APR10 and ’Not Earlier Than’ start of 26APR10. The activity has a 5 day duration.

The software allows this to happen and there are no messages in the log file about this. However I would like to know if this SHOULD be allowed. I would have thought one of the constraints would be ignored or at least a warning message should appear on screen when rescheduling.

Is it a software bug or is it conceptually possible?
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Replies

Tue, 2010-04-13 03:01
#1
Shah. HB
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Hi to all

I would to share similar issue i faced .I just linked two items in the schedule with FS relationship.

Item 1 is assigned as start milestone and
Item 2 is assigned finish Milestone.

On running F9 the Item 2 which is chronologically the last one got the early dates one day earlier than item 1.



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Mon, 2010-04-12 21:05
#2
Rafael Davila
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Kevin,

I agree with you, if some constraint functionality is to be applied it should be in the form of a marker that will highlight on the activity line a target or contractual date but with no effect on the network logic.

I have been asking for this for years but seem like the PMI and others can live with it as good practice, even a single occurrence can be enough to distort the network computations making it meaningless or impossible to follow the logic. The complications of real life modeling and resource constraining are a real and necessary need enough comlpicated enough to drive someone crazy, then why add unnecessary additional complications with date constraints, is not needed to highlight the target?

Best regards,
Rafael
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Mon, 2010-04-12 17:46
#3
Kevin Button
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Thanks Gary, that’s pretty much what I thought. As a long time Primavera user and now Open Plan, I have always been against the use of Mandatory or Fixed constraints that ignore all network logic. If it were up to me they wouldn’t exist in any software.

Cheers
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Mon, 2010-04-12 04:07
#4
Gary Whitehead
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It’s clearly not conceptually possible to have an activity planned to start after it’s planned to finish.

I wouldn’t call it a software bug, more that Open Plan has never been hot on checking the integrity of the data entered. Unless it causes an error in the algorithms they use (eg logical loops), you probably won’t get a log or error message from Open Plan.

You could argue that Open Plan shouldn’t allow it, but you could also argue that the user shouldn’t be entering such data in the first place. Ultimately, no amount of data validation by the software will completely insure against a numpty at the keyboard!

This is one of the many reasons why people should be very careful when using constraints in schedules, particular the ’fixed’ types which overide logic and float calculations.

Cheers,

G
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