When planning the production of a marketing brochure for instance, you could use lead time to
make the creation of artwork start a few days before the writing phase is over. The two tasks are
however still linked, which means that a delay of the writing phase will also delay the creation of
the artwork.
Adding Constraints to a Gantt Chart (these constraints are not available in GanttProject)
Constraints define the degree of flexibility available to the Gantt application when scheduling or
rescheduling a task by imposing restrictions on its start or end date. The following task constraint
types offer different degrees of flexibility.
Two "constraints" are actually so flexible that they are not generally regarded as constraints at all:
As Soon As Possible (ASAP): This is generally the default constraint when you schedule
your project from its start date, as is normally the case. You should try to keep this default
whenever possible as it gives the software the most scheduling flexibility. If you apply this
constraint to an unlinked task, the task will be scheduled to start at the project start date. If
you apply it to a linked task, it will start as soon as the dependencies with its predecessor
tasks will allow.
As Late As Possible (ALAP): This is generally the default constraint when you schedule
your project from its end date. If you apply this constraint to an unlinked task, the task will
be scheduled so that its end date coincides with the end date of the overall project. If you
apply it to a task linked to a successor task, the task will be scheduled to end when the
successor needs to start. On the whole, you should avoid this constraint as it does not
leave any slack time to deal with possible problems. Any delay on the task is likely to
impact the overall end date.
The following constraints all restrict the Gantt application's flexibility when scheduling tasks.
Although you might be tempted to use them if you are new to project management, you need to
make sure you understand the implications. Keeping their use to a minimum (especially the last
two) will allow you to take full advantage of the automatic scheduling possibilities.
Start No Earlier Than (SNET): This means that the task, whether linked or not, may not
start before the given date. However, the Gantt application still has the flexibility to start the
task later than the given date.
Start No Later Than (SNLT): This means that the task, whether linked or not, may not start
later than the given date. However, the Gantt application still has the flexibility to start the
task earlier than the given date.
Finish No Earlier Than (FNET): This means that the task, whether linked or not, may not
end before the given date. However, the Gantt application still has the flexibility to end the
task later than the given date.
Finish No Later Than (FNLT): This means that the task, whether linked or not, may not
end later than the given date. However, the Gantt application still has the flexibility to end
the task earlier than the given date.
Must Start On (MSO): This rigid constraint means that the task, whether linked or not,
must start on the given date. Even if the preceding task is completed earlier, the Gantt
application cannot pull in the constrained task to take advantage of the time gained.
Must Finish On (MFO): This rigid constraint means that the task, whether linked or not,
must end on the given date. As above, even if the preceding task is completed earlier, the
Gantt application cannot pull in the constrained task to take advantage of the time gained.