What kind of schedule activity constraint in Primavera P6 Professional would you use to model the situation where you have to deliver a report no later than a specified date? And you, of course, can deliver the report earlier, but this date is the do-or-die finish date.
Ideally you want your activity durations and associated relationships (network logic) to drive the completion dates of your activities. Scheduling guidelines recommend limiting the use of constraints because they are static and do not adjust to changes in activity durations and/or logic.
Schedule updates do not propagate through constraints. You therefore must manually inspect and update your constraints, accordingly. However, you may have an external constraint that puts a binding restriction on the latest date your activity can complete. In the Finish On or Before (FOOB) Primavera P6 constraint network logic is free to decide the task finish date, provided the task finish falls on the timescale to the left of the FOOB constraint date. However, if the finish date falls beyond (to the right) of the FOOB constraint date then the FOOB constraint warns that you have a project scheduling issue.
This article describes when and how to use the FOOB constraint in Primavera P6 Professional.
The FOOB constraint fits well with our report project example. If the network logic and schedule progression have the report completing before the deadline, P6 has no issues with the report delivery. However, when the logic or schedule progression has the report completing beyond the deadline then P6 provides a warning. P6, however, will not make the FOOB constraint violate network logic.
The Primavera P6 Gantt chart still honors the activity relationships. Note in Microsoft Project that the corresponding Start No Later Than (SNLT) or Finish No Later Than (FNLT) constraints will violate activity relationships. In Project the SNLT and FNLT constraints take precedence over logic dependencies.
In Primavera P6 the FOOB constraint does not; the schedule finish date still depends on network logic. You will, however, see negative total float in the activities table, which warns you there is a problem.
When it comes to deadlines Microsoft Project has an advantage over Primavera P6 Professional. In Microsoft Project you may display deadlines on the Gantt chart and list them in the activities table. In this way with Project you may see the projected completion date of your activity in relation to the activity deadline date.
It is possible in Primavera P6, however, to mark activities on the Gantt chart that have a constraint. This way you at least know which activities to watch closely. P6 also has a negative float bar, so as soon as your schedule is in danger of missing your constraint date you have a negative float bar warning, again, on the Gantt chart. This negative float bar tells you which activities to adjust and by how much to align your schedule with the deadline date.
Let’s now look at a demonstration schedule that uses Primavera P6 FOOB constraints. In Figure 1 we have a schedule that includes three FOOB constraints.
Each FOOB constraint was inserted on the desired activity in the bottom details status tab, Figure 2.
In Primavera P6 the only reason we know the constraints are present is because the activities table lists the primary constraint and primary constraint date for each activity. However, use the bars feature to activate the finish constraint bar, Figure 3.
For each bar that meets the bar ‘Has Finish Constraint’ filter criteria, Figure 4, a semi-triangular or wedged shaped light blue image is inserted at the end of each activity.
Note, in particular, ‘Adjust Data & Plot’ activity and ‘Perform Model Modal Analysis’ activity. This image also appears on the contract completion date milestone, but is not visible because the milestone is overlaid on top of the FOOB constraint wedge image. This is unfortunate.
It is also helpful to activate the negative float bar, Figure 5, so that we can see directly on the Gantt chart if any activity is falling behind the constraint dates.
In Figure 5, note the negative float bar filter. In Figure 6 we extend the length of ‘Adjust Data & Plot’ activity by two days, which makes the schedule miss the ‘Adjust Data & Plot’ FOOB constraint by 2 days.
Activities with the yellow negative float bars beneath are all activities that could be adjusted to meet the’ Adjust Data & Plot’ FOOB constraint. So the negative float bars show us where to make adjustments. The Perform ‘Model Modal Analysis’ activity has no associated negative float bars, which tells us it is on schedule.
The Primavera P6 Professional FOOB constraint helps model the situation where interim or final deliverable submission is acceptable on any completion date provided it is on or before the activity deadline.
Microsoft Project deadline features benefit from a symbol that is placed on the actual activity deadline date. In this way in Project you may track activity progress in relation to the deadline. Primavera P6, unfortunately, does not have this feature. Primavera P6 does, however, enable you to mark activities that have a FOOB deadline constraint, so you know which activities to closely watch.
You can also look to total float in the activities table to scan for activities with negative total float, which is a warning that your schedule has an issue.
Primavera P6 additionally has the negative float bar that will highlight all activities on the Gantt chart that have negative total float. This provides a more apparent warning directly on the Gantt chart when there is a problem.
So in Primavera P6 you know which activities are FOOB constrained and you are warned when there is a FOOB related schedule issue. And P6 FOOB constraints will not violate network logic, which is a huge plus.