Constraining Tasks | Mastering Microsoft Project 2002

When you create a project, you can schedule the project to start on a specified date or to finish on a specific date. When you set a project start date, tasks are scheduled to start as soon as possible. When you set a project finish date, tasks are scheduled to start as late as possible. The “as possible” part is determined by the relationships (links) that you establish between tasks. Both the As Soon As and As Late As Possible constraints are directly related to the start or finish date of a predecessor task.

Note

To review the project information for the current project, choose Project Ø Project Information. For more about scheduling the project start or finish date, see “Setting Up Project Information” in Chapter 6.

Other factors, as well, may constrain the actual start or finish date of a particular task. For example, if one of the project’s tasks is to meet with an individual to review the project and that person is going to be out of town for the period of time you want to meet, the project’s schedule can be negatively affected. You can account for this and other scheduling problems by assigning a constraint to the task.

Understanding Constraint Types

In Project, you can choose from the eight constraint options described in Table 8.1.

Table 8.1: Constraint Types
Constraint Type	Description
As Late as Possible	This is the default constraint type when a project is scheduled from the Finish date. Project schedules the task to start as late as it can. The task is scheduled to start as late as it can, based on its relationships and other scheduling parameters.
As Soon As Possible	This is the default constraint type when a project is scheduled from the start date. Project schedules the task to start as early as it can, based on its relationships and other scheduling parameters.
Finish No Earlier Than	The task must be not be completed before the established constraint date.
Finish No Later Than	The task must finish by the established constraint date.
Must Finish On	The task must finish on the established constraint date.
Must Start On	The task must start on the established constraint date.
Start No Earlier Than	The task must not start before the established constraint date.
Start No Later Than	The task must start on or before the established constraint date.

Applying Constraints

To apply a constraint to a task, follow these steps:

Click the Task Information button on the Standard toolbar, or double-click a task to open the Task Information dialog box.
Click the Advanced tab.
Click the drop-down arrow to open the Constraint type list.
Choose the desired constraint from the list.
Open the drop-down list in the Constraint Date field to select a date for the constraint (As Soon As Possible and As Late As Possible do not need a constraint date).
Click OK.

Flexible vs. Inflexible Constraints

Inflexible constraints are constraints that restrict scheduling because they require that a task start or finish within specific parameters. Flexible constraints allow Project to calculate the schedule and make appropriate adjustments based on the constraints applied. Table 8.2 shows a list of inflexible and flexible constraints, depending on whether the project is scheduled from the start date or the finish date.

Table 8.2: Inflexible and Flexible Constraints
Type	Projects Based on Start Date	Projects Based on Finish Date
Flexible constraints	As Soon as Possible	As Soon as Possible
	As Late as Possible	As Late as Possible
	Finish No Earlier Than	Finish No Later Than
	Start No Earlier Than	Start No Later Than
Inflexible constraints	Must Finish On	Must Finish On
	Must Start On	Must Start On
	Finish No Later Than	Finish No Earlier Than
	Start No Later Than	Start No Earlier Than

When applying constraints, apply inflexible constraints only when they are absolutely necessary. When you apply inflexible constraints, you are restricting Project from establishing a schedule for all the tasks that is consistent with the durations and other scheduling parameters you have assigned to tasks. If, for example, you apply an inflexible constraint to a task, it may be impossible to complete the predecessor or successor tasks within the constraint. When this occurs, Project displays the Planning Wizard message, shown in Figure 8.21, and asks you how you want to handle the conflict. Select Cancel to remove the constraint and avoid the scheduling conflict, or select Continue to save the constraint and allow the scheduling conflict.

Tip

For help resolving scheduling conflicts caused by constraints, see “Resolving Constraint Conflicts,” later in this chapter.

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Figure 8.21: Project warns you when a constraint creates a conflict.

Reviewing Constraints

Project indicates that a constraint is applied to a task by adding a calendar icon to the Indicators field for that task in the Task Entry table. A blue square on the right side of the calendar icon indicates a flexible task constraint; a red square on the left side indicates an inflexible task constraint. Point to the calendar icon to display more information about that particular constraint. (For more about flexible and inflexible tasks constraints, see “Resolving Constraint Conflicts” later in this chapter.)

Warning

You can inadvertently apply a constraint to a task by dragging the task in the Gantt Chart view. Moving a task automatically applies a Start No Earlier Than constraint to the task. Check the Indicators field in the Task Entry table to see which tasks have constraints applied.

Removing Constraints

You can remove a constraint by applying an As Soon as Possible constraint to a task in a project scheduled from the start date, or applying the As Late as Possible constraint to a task in a project scheduled from the finish date.

To remove constraints on more than one task, follow these steps:

Select the tasks in the Task Entry table by dragging to select successive tasks, or by holding Ctrl and clicking to select nonconsecutive tasks.
Click the Task Information button on the Standard toolbar, or choose Project Ø Task Information from the menu. The Multiple Task Information dialog box opens.
Click the Advanced tab.
Click the drop-down arrow to open the Constraint type list.
Choose As Soon As Possible in a project scheduled from the start date, or choose As Late as Possible in a project scheduled from the finish date.
Click OK to save the new constraint types.

Warning
Any information you change in the Multiple Task Information dialog box affects all the selected tasks, so be careful to only change things that you want reflected in all those tasks.

Resolving Constraint Conflicts

Constraint conflicts arise when you apply constraints that are in conflict with other parts of the schedule. For example, if you apply a Start No Later Than constraint to a task in the Office Decentralization project such as Order Furniture, and specify a date that actually precedes the finish date of the predecessor Assign Offices, Project cannot resolve the conflict. You must decide whether the constraint is necessary, or whether there is some other way to schedule the tasks to avoid the conflict.

Ask the following questions to determine how to resolve the conflict:

Is the constraint really necessary? Was the constraint applied intentionally or accidentally? What would have to change in the project plan in for the constraint to be removed?
Can the finish date of the predecessor task be changed so that it is actually completed by the constraint date?
Can the duration of the predecessor task be changed so that it can be completed by the constraint date? This may make it necessary to assign additional resources to the task. For more about using resources to resolve conflicts, see Chapter 9.
Is it possible to unlink the tasks that are in conflict? Perhaps the task with the constraint would be better linked to a different task or not linked to any task.
Can the constraint be changed from an inflexible constraint to a flexible one? For example, could the restraint be changed from a Must Start On to a Start No Earlier Than constraint?

Not Honoring Constraint Dates

Another way to resolve constraints is simply to not honor them in the schedule. By default, Project always honors constraint dates. You can turn this option off by following these steps:

Choose Tools Ø Options and then click the Schedule tab.
Click to deselect the Tasks Will Always Honor Their Constraint Dates check box.
Click OK to save the new settings.

When this Always Honor option is turned off, Project notes the conflicts but continues to calculate the schedule as if the conflicting constraint weren’t applied.

Setting a Deadline

Rather than setting an inflexible constraint that might negatively affect scheduling, you can now record a deadline date in Project 2002. A deadline is the date you want or need a task to be completed. Setting a deadline does not affect the task schedule in any way; however, if the deadline passes and the task is not completed, Project displays an indicator in the Indicator column.

To set a deadline, follow these steps:

In the Gantt Chart view, select the task for which you want to set a deadline, then click the Task Information icon on the Standard toolbar.
When the Task Information dialog box appears, select the Advanced tab.
Under Constrain Task, type or select the deadline date.
Click OK.

Project notes a deadline in the Gantt chart with a down-pointing arrow. If the deadline is before the scheduled end date, the arrow appears in the middle of the Gantt chart bar.