Contraints

Eric,



A very nice effort! You have made one error twice. Under Items 1 & 3 (Early Start & Early Finish Constraints), "Logic Calculation", you state that "P3 allies it only during the backward scheduling calculation." I think you meant to state during the FORWARD calculation.



I also would recommend that you recommend that only the least constraining constraint be used when applying constraints. Use a Start No Earlier Than instead of a Start ON if it will suffice.



Ron Winter.

Attached is a comprehensive write-up by myself regarding Using Constraints in P3. This is a serious topic which many people ignored and misused. I am also welcome feedbacks.



Go to the

http://www.htcprojectcontrols.com/TTB2004-4.pdf



(Note that I have made the corrections based on Ron’s comments. Thanks.)

Eric Chou, PE

HTC Project Controls, Inc.

Constraints is mainly useful for the following conditions:



1)To specify contractual dates/dates which are not directly in your control



2)During updating of schedules,when any of the activity is not very much relevant but the progress is not 100% becos of the Progress Measurement system.For example mainly engg activities.



Regards

Mani

One example of where I use constraints is where the date may not be achieved by relationships and often they may be found in contracts. For example:



1. The availability of a site from the client.

2. The required date that a project or part of a project must be complete by.

3. A date legislated by a government by which certain work must be completed by.

4. A date that a subcontractor states he or some equipment etc will be available on or must be released by.



Regards

Paul E Harris

www.eh.com.au

One of the important uses of a CPM schedule is to display the cause and effect relationship of unexpected events and local delays to overall project delay.



If your schedule uses non-mandated constraints, then the effect of delaying activities in one area may not show the effects in another area. In this case, what you have is a barcharting program, not a CPM.

hi...

the constraint is useful when you couldnt define a suitable predecessors for activities and you wanna the specify specific date for acitivity.

but in some cases, constraints broke the chain of activities and make a negetive TF to network that we have to fix the problems by using the corrected type of constraints.

Hi...



Constraint is one of the most useful feature of a planning software if use properly. The problem is some planner is tempted to use this feature unnecessarily for the sake of ease.



regards,



kabayan

Hi Kabayan,



I believe constraints is not about advantages or disadvantages. This is about the nature of the beast.



Ideally, schedules should be prepared with less constraints in order for you to have a dynamic schedule wherein any change to your schedule could be reflected on the entire project. But reality is not like this. For ex. NTP is usually constrained as early start in P3 or start no earlier than constraint in MSP. Some planners uses a more inflexible constraint such as mandatory start or finish. Project deliverables may be constrained as mandatory.



What I mean here kabayan is, it depends on the nature of activities. In scheduling, constraints makes your plan stiff and inflexible



Regards,



Se

Moises:



The only thing I can tell you about that is that you need to verify their validity, and whether they are mandatory or preferential constraints. Can the preferential constraints be eliminated and not put an unneeded burden on the schedule?



Tomas Rivera

Altek System

Scehduling of high performance

construction projects

Perhaps I am misunderstanding your question, but a schedule without logical restraints is just a picture. You need constraints to perfom critical path analysis.



[edit]I see I did mis-understand the question. I was referring to predecessor/successor relationships.[/edit]



Bernard Ertl

InterPlan Systems Inc. - Project Management Software, Project Planning Software