See task relationships by using Task Path

When fine-tuning task relationships, you need to keep track of the predecessor tasks that affect the scheduling of their successor tasks. In complex plans, visually identifying predecessor and successor relationships is not always easy. This is especially true when a single task has multiple predecessors or successors.

The Task Path feature applies color formatting to the Gantt bars of the selected task’s predecessor and successor tasks. Task Path can also distinguish a task’s driving predecessors (the predecessor tasks that directly determine, or drive, the start date of the task) from that task’s other predecessors. (Predecessor tasks that can slip without rescheduling their successor tasks are said to have slack—see Chapter 10.) The Task Path feature can also do the same for driving successor tasks.

The distinct color highlighting applied to driving predecessor and successor tasks is especially useful when you’re focused on managing the overall duration of a sequence of linked tasks. Without Task Path formatting applied, determining the path of related tasks on a Gantt chart can be difficult. In Figure 9-1, you can see the standard formatting, which does not distinguish predecessor or successor tasks on a Gantt chart.

To identify the chain of a task’s predecessor tasks, turn on Task Path predecessor formatting, as displayed in Figure 9-2.

A task can have a long chain of predecessor tasks, but which of these directly drive the scheduling of the task? Task Path can visually distinguish these driving predecessors too, as shown in Figure 9-3.

Some predecessor tasks directly drive the scheduling of a task and are its driving predecessors. Other predecessor tasks might have some amount of slack between them and the selected task. With Task Path highlighting applied, you can more easily see which tasks are currently determining the scheduling of the selected task. Any schedule changes to these driving predecessor tasks affect the selected task.

In addition to predecessor highlighting, you can use Task Path to highlight the selected task’s successor tasks, illustrated in Figure 9-4.

Project applies a light purple highlight formatting to the Gantt bars of a task’s successor tasks.

To apply Task Path formatting to a task’s predecessor or successor tasks

1. In a Gantt chart view, select a task name.

2. On the Gantt Chart Format tab, in the Bar Styles group, select the Task Path button and then select the options you want.

To turn off all Task Path formatting

• On the Gantt Chart Format tab, in the Bar Styles group, select the Task Path button and select Remove Highlighting.

Adjust task link relationships

You might recall from Chapter 4, “Build a task list,” that Project uses four types of task dependencies, or relationships:

• Finish-to-start (FS) The finish date of the predecessor task determines the start date of the successor task.

• Start-to-start (SS) The start date of the predecessor task determines the start date of the successor task.

• Finish-to-finish (FF) The finish date of the predecessor task determines the finish date of the successor task.

• Start-to-finish (SF) The start date of the predecessor task determines the finish date of the successor task.

When you link tasks in Project by using the Link Tasks button on the Task tab, in the Schedule group, Project gives those tasks a finish-to-start relationship, by default. This is fine for many tasks, but you will most likely change some task relationships as you fine-tune a plan. For example, the following tasks require relationships other than finish-to-start:

• You can start setting pages as soon as you start illustration work on a book project (a start-to-start relationship, as Figure 9-5 shows). This reduces the overall time required to finish the two tasks because they are completed in parallel.

  

• Planning the editorial work for a book can begin before the manuscript is complete, but it cannot be finished until the manuscript is complete. You want the two tasks to finish at the same time (a finish-to-finish relationship, as Figure 9-6 shows).

  

Task relationships should reflect the sequence in which work needs to be performed. After you’ve established the correct task relationships, you can fine-tune your schedule by entering overlap (lead time) or delay (lag time) between the finish or start dates of predecessor and successor tasks.

When two tasks have a finish-to-start relationship:

• Lead time causes the successor task to begin before its predecessor task concludes.

• Lag time causes the successor task to begin sometime after its predecessor task concludes.

Consider an example of how lead and lag time affect task relationships. Assume that you initially planned three tasks—copyedit, author review, and copyedit incorporation—by using Project’s default finish-to-start relationships, shown in Figure 9-7.

Before task 2 can begin, you need to allow an extra day for the copyedited manuscript to be shipped to the author. You don’t want to add a day to the duration of task 1 because no real work will occur on that day. Instead, you enter a 1-day lag between tasks 1 and 2, as illustrated in Figure 9-8.

However, task 3 can start as soon as task 2 is halfway completed. To make this happen, you enter 50 percent lead time between tasks 2 and 3, illustrated in Figure 9-9.

You can enter lead and lag time as units of time, such as 2 days, or as a percentage of the duration of the predecessor task, such as 50%. Enter lag time in positive units, and enter lead time in negative units (for example, –2d or –50%). You can apply lead or lag time to any type of task relationship: finish-to-start, start-to-start, or any other type.

Places where you can enter lead or lag time include the Task Information dialog (available from the Task tab), the Predecessors column in the Entry table, the Task Form (displayed by selecting the Details command on the View tab in the Split View group), and the Task Dependency dialog (opened by double-clicking a link line between Gantt bars).

To change the type of task relationship between tasks

1. Select a successor task that you want to change.

2. On the Task tab, in the Properties group, select the Information button to open the Task Information dialog, which contains details about the currently selected task.

   Tip

   Double-clicking a task name is a quick way to open the Task Information dialog.

3. Select the Predecessors tab.

4. On the Predecessors tab, in the Type column for the predecessor task, select the relationship type you want between the tasks and then select OK.

5. Select OK to close the Task Information dialog.

To add lead or lag time between linked tasks

1. Select the successor task to which you want to add lead or lag time.

2. On the Task tab, in the Properties group, select the Information button.

3. In the Task Information dialog, select the Predecessors tab and then do either of the following:

   • In the Lag field for a predecessor task, enter the lead value you want. Lead values are entered as negative lag values. Lead can be a number of working days (for example, –2d) or a percentage of the duration of the predecessor task (for example, –25%).

   • In the Lag field for a predecessor task, enter the lag value you want. Lag values are entered as positive values. Lag can be a number of working days (for example, 3d) or a percentage of the duration of the predecessor task (for example, 50%).

Control task scheduling by using constraints

Every task that you enter into Project has some type of constraint applied to it. A constraint determines the degree to which an automatically scheduled task can be rescheduled. You can manage the constraint details of automatically scheduled tasks. When working with a manually scheduled task, however, you cannot change the constraint type or set a constraint date: Project doesn’t schedule manually scheduled tasks, so constraints have no effect. For more information about manually scheduled tasks and automatically scheduled tasks, see Chapter 4.

Constraints fall into three categories:

• Flexible constraints Project can change the start and finish dates of a task. Project’s default constraint type causes tasks to start as soon as possible. This type of flexible constraint is called As Soon As Possible, or ASAP. No constraint date is associated with flexible constraints. Project does not display any special indicator in the Indicators column for flexible constraints.

• Semi-flexible constraints With this type of constraint, a task has a start or finish date boundary. However, within that boundary, Project has the scheduling flexibility to change the start and finish dates of a task. For example, consider a task that must finish no later than June 20, 2025, but that could finish before this date. Semi-flexible constraints are sometimes called soft constraints or moderate constraints. When a semi-flexible constraint has been applied to a task, Project displays a special constraint indicator (which looks like a calendar) in the Indicators column.

• Inflexible constraints With this type of constraint, a task must begin or end on a certain date. For example, you can specify that a task must end on November 14, 2025. Inflexible constraints are sometimes called hard constraints. When an inflexible constraint has been applied to a task, Project displays a constraint indicator in the Indicators column. As Figure 9-10 shows, you can point to a constraint indicator to display the constraint details in a ScreenTip.

  

Project uses eight types of task constraints, as you can see in the following table:

These three constraint categories have different effects on task scheduling:

• Flexible constraints These constraints, such as As Soon As Possible (ASAP), allow tasks to be scheduled without any limitations other than their predecessor and successor relationships and the project’s start date (for ASAP task constraints) or finish date (for As Late As Possible, or ALAP, task constraints). With these constraint types, no fixed start or end dates are imposed on tasks. Use these constraint types whenever possible. See Figure 9-11 for a flexible ASAP constraint example.

  

  For example, consider a schedule in which tasks A and B are linked and task B has an ASAP constraint applied. As the duration of task A shrinks or grows, the start date of task B is automatically adjusted accordingly.

• Semi-flexible constraints These constraints, such as Start No Earlier Than or Start No Later Than (SNET or SNLT), limit the rescheduling of a task within the date boundary you specify. See Figure 9-12 for an illustration of an SNET constraint.

  

  With an SNET type of constraint, tasks A and B are linked and task B has an SNET constraint set to day 4. If task A’s duration decreases, the start of task B is unaffected. However, if task A’s duration extends, Project adjusts task B’s start date automatically.

• Inflexible constraints These constraints, such as Must Start On (MSO), prevent the rescheduling of a task, as shown in Figure 9-13. Use these constraint types only when absolutely necessary.

  

  In this example, tasks A and B are linked, and task B has an MSO constraint set to day 4. Whether task A’s duration decreases or increases, the start of task B is unaffected.

The type of constraint you apply to the tasks in your plans depends on what you need from Project. Use inflexible constraints only if the start or finish date of a task is fixed by factors beyond the control of the project team. Examples of such tasks include handoffs to clients and the end of a funding period. For tasks without such limitations, use flexible constraints. Flexible constraints provide the most discretion in adjusting start and finish dates, and they allow Project to adjust dates if your plan changes. For example, if you’re using ASAP constraints and the duration of a predecessor task changes from 4 days to 2 days, Project adjusts, or pulls in, the start and finish dates of all successor tasks. However, if a successor task has an inflexible constraint applied, Project cannot adjust its start or finish dates.

Keep a few other points in mind when applying constraints to tasks:

• Entering a finish date for a task (for example, in the Finish column) applies a Finish No Earlier Than constraint to the task.

• Entering a Start date for a task (for example, in the Start column) or dragging a Gantt bar directly on the Gantt chart applies a Start No Earlier Than constraint to the task.

• In many cases, entering a deadline date is a better alternative than entering a semi-flexible or inflexible constraint. You’ll work with deadline dates in Chapter 10.

• Unless you specify a time, Project schedules a constraint date’s start or finish time by using the Default start time or Default end time value that is set on the Schedule tab of the Project Options dialog. (To open this dialog, select the File tab to display the Backstage view, and then select Options.) The default start time is 8:00 AM. If you want a constrained task to be scheduled to start at a different time, enter that time along with the start date. For example, if you want to schedule a task to start at 10:00 AM on July 21, 2025, enter July 21 25 10AM in the Constraint date field.

• If you must apply semi-flexible or inflexible constraints to tasks in addition to task relationships, you might create what’s called negative slack. For example, assume that you have a successor task that has a finish-to-start relationship with its predecessor task. If you enter a Must Start On constraint for the successor task earlier than the finish date of the predecessor task, this results in negative slack and a scheduling conflict. By default, the constraint date applied to the successor task overrides the relationship. However, if you prefer, you can set Project to honor relationships over constraints. To do so, in the Project Options dialog, on the Schedule tab, clear the Tasks will always honor their constraint dates checkbox.

• If you must schedule a project from a finish date instead of a start date, some constraint behaviors differ. For example, the As Late As Possible constraint type then becomes the default for new tasks (instead of the As Soon As Possible constraint type). Pay close attention to constraints when scheduling from a finish date to make sure that you create the effect you intend.

To apply a task constraint

1. Select the name of the task to which you want to apply a constraint.

   Important

   The task must be automatically scheduled; task constraints do not apply to manually scheduled tasks.

2. On the Task tab, in the Properties group, select Information.

   Tip

   Double-clicking a task name is a quick way to open the Task Information dialog.

3. In the Task Information dialog, select the Advanced tab.

4. In the Constraint type box, select the constraint type you want.

5. All constraint types except As Soon As Possible and As Late As Possible require a constraint date. In the Constraint date box, enter or select the date you want, and then select OK.

To remove a task constraint

1. Select a task that has had a constraint applied.

2. On the Task tab, in the Properties group, select the Information button.

3. In the Task Information dialog, select the Advanced tab.

4. In the Constraint type box, select As Soon As Possible or (if scheduling from the project finish date) As Late As Possible and select OK.

   Tip

   The Constraint date will automatically return to NA after you select OK.

Interrupt work on a task

When initially planning project tasks, you might know that work on a certain task will be interrupted. Instead of listing a task twice to account for a known interruption in work, you can split the task into two or more segments. You might want to split a task in these situations:

• You anticipate an interruption in a task. This might be the case, for example, if the facility where a task must be performed will not be accessible midway through the task’s duration.

• A task is unexpectedly interrupted. After a task is underway, a resource might have to stop work on the task because some other issue has taken priority. When the other issue is resolved, the resource can resume work on the task.

As Figure 9-14 shows, you use the Split Task command and drag the mouse pointer within a Gantt bar to split the task into multiple segments.

After you split a task, Project draws a dotted line between the two segments of the task in Gantt chart views.

Keep a few other tips in mind when splitting tasks:

• You can drag a segment of a split task either left or right to reschedule the split.

• The time of the task split, represented by the dotted line, is not counted in the duration of the task. No work occurs during the split.

• You can hide the dotted line between segments by clearing the Show bar splits checkbox in the Layout dialog. (You can access this dialog by selecting the Layout button in the Format group on the Gantt Chart Format tab.)

• If the duration of a split task changes, the last segment of the task increases or decreases accordingly.

• If a split task is rescheduled (for example, if its start date changes), the entire task is rescheduled, splits and all. The task keeps the same pattern of segments and splits.

• Leveling resources or manually contouring assignments over time can cause tasks to split. You contour assignments in Chapter 11, “Fine-tune resource and assignment details,” and level resources in Chapter 12, “Fine-tune the Project plan.”

To split a task into multiple segments

1. If the task’s Gantt bar is not visible in the chart portion of the Gantt chart view, select the task name and then, on the Task tab, in the Editing group, select Scroll to Task.

2. On the Task tab, in the Schedule group, select the Split Task button (which looks like a broken Gantt bar) to display a ScreenTip and change the mouse pointer to task-splitting mode.

3. Move the mouse pointer over the Gantt bar of the task (but don’t select) until the start of the split you want appears in the ScreenTip.

4. Select, and then drag the mouse pointer to the right until the start date that you want for the new segment appears in the ScreenTip. Release the mouse button.

To reschedule the second segment of a split task

• Drag the second or later segment of the task to the new start date that you want.

To rejoin two segments of a split task

• Drag the start of the later segment to the finish of the earlier segment until the two segments rejoin into one segment.

Adjust working time for individual tasks

Occasionally, you want a specific task to occur at a time that differs from the working time of the project calendar. Or perhaps you want a task to occur at a time outside the assigned resource’s normal working time, as determined by the resource’s calendar. To accomplish this, you apply a task calendar to such tasks. As with the project calendar, you specify which base calendar to use as a task calendar. You might need a task calendar in these situations:

• You’re using the Standard base calendar as your project calendar, with 8:00 AM to 5:00 PM as your normal working hours, and you have a task that must run overnight.

• You have a task that must occur on a specific weekday.

• You have a task that must occur over a weekend.

Project treats tasks differently from resources: It doesn’t create calendars as you create tasks. (If you need a refresher on resource calendars, see Chapter 5, “Set up resources.”) When you need a task calendar, you assign a base calendar to the task. This base calendar might be one that Project provides or a new base calendar that you create.

For tasks that have both a task calendar and resource assignments, Project schedules work during the working times that are common between the task calendar and resource calendars. If the calendars have no common working time, Project alerts you when you apply the task calendar or assign a resource to the task.

When you apply a task calendar to a task, you can choose to ignore resource calendars for all resources assigned to the task. Project then schedules the resources to work on the task according to the task calendar, not their own resource calendars (for example, to work 24 hours per day).

To create a new base calendar

1. On the Project tab, in the Properties group, select the Change Working Time button to open the Change Working Time dialog.

2. In the Change Working Time dialog, select Create New Calendar to open the Create New Base Calendar dialog shown in Figure 9-15.

   

3. In the Name box, enter the name of the new base calendar and then do either of the following:

   • To create a new calendar with working times of Monday through Friday, 8:00 AM to 5:00 PM, select Create new base calendar.

   • To create a new calendar that initially matches an existing base calendar, select the Make a copy of option and then select the base calendar you want from the list.

4. Select OK.

5. To enter the working time details for this new calendar, in the Change Working Time dialog, on the Exceptions and Work Weeks tabs, enter the specific working time exceptions or global changes you want for this calendar.

6. Select OK to close the Change Working Time dialog.

To apply a base calendar to a task

1. Select the name of the task to which you want to apply the base calendar.

2. On the Task tab, in the Properties group, select the Information button to open the Task Information dialog displayed in Figure 9-16.

3. Select the Advanced tab.

4. In the Calendar box, select the base calendar from the list of available base calendars.

   

5. Select Scheduling ignores resource calendars to schedule assigned resources to follow the specified task calendar.

6. Select OK to close the dialog. Project applies the base calendar to the task; for this task, the base calendar is its task calendar. A calendar icon appears in the Indicators column, reminding you that this task has a task calendar applied to it.

7. To see the calendar details, point to the calendar icon. A ScreenTip appears, showing the calendar details, as Figure 9-17 shows.

   

Control task scheduling by using task types

You might recall from Chapter 6, “Assign resources to tasks,” that Project uses the following formula to calculate a task’s work value:

Duration × Assignment Units = Work

Each value in this formula corresponds to a task type. A task type determines which of the three values remains fixed if the other two values change. You can change a task’s type to better control its scheduling as you change its work, duration, or assignment units values.

The default task type is fixed units: if you change a task’s duration, Project recalculates work. Likewise, if you change a task’s work, Project recalculates the duration. In either case, the units value is not affected.

The two other task types are fixed duration and fixed work. For these task types, when Project responds to schedule changes, it records the highest units value per assignment in a field called Peak.

For a fixed-work task:

• You can change the assignment units value; Project recalculates the duration.

• You can change the duration value; Project recalculates peak units. The assignment units value is not affected.

For a fixed-duration task:

• You can change the assignment units value; Project recalculates work.

• You can change the work value; Project recalculates peak units. The assignment units value is not affected.

You can change a task type at any time. Note that characterizing a task type as fixed does not mean that its duration, assignment units, or work values are unchangeable. You can change any value for any task type.

Which is the right task type to apply to each of your tasks? It depends on how you want Project to schedule that task. See Figure 9-18 for a summary of changing values and the results based on task type.

These pointers summarize how changing values causes a recalculation:

• If you have a fixed-duration task, work is recalculated, unless you change work— then Project recalculates peak units.

• If you have a fixed-units task, duration is recalculated, unless you change duration—then Project recalculates work.

• If you have a fixed-work task, duration is recalculated, unless you change duration—then Project recalculates peak units.

Changing a task type has no immediate effect on a plan. To better see the effect of task types, consider an example of how task types determine the way tasks are rescheduled in response to a change in duration, work, or assignment units.

Consider the new book plan, which can be shown in a customized Task Usage view (with the addition of the Peak field) with the Task Form visible. With this view combination, you can see work, duration, assignment units, and peak values. This example focuses on task 8, Copyedit. As Figure 9-19 shows, its task type is fixed units, the default task type.

Task 8, with the default task type of Fixed Units, has a total work value of 240 hours, a resource assignment units value of 200% (that’s the equivalent of two full-time copyeditors), and a duration of 15 days. When you increase the task’s duration to 20 days, you can observe the effects on the other values.

After the task’s duration is changed to 20 days, Project increases the work to 320 hours. Change highlighting is applied to the Work and Finish date values as shown in Figure 9-20.

As expected, the assignment units values did not change with this fixed-units type of task.

Now look at what happens when you start with the original 15-day duration task and 240 hours of work but this time make it a fixed-duration task and change its work value. After you change the task’s work to 320 hours, Project updates peak units but keeps the duration the same, as Figure 9-21 shows.

The copyeditors’ increased peak units value of 267% appears in the Peak field. This value accounts for the schedule change, while Project preserves the original assignment units value of 200%, as shown in the Task Form.

Changing a task’s default task type lets you “lock in” how Project handles one of the three assignment calculation variables as either of the other two variables changes. However, you always have the final word on how a task responds to changed assignment calculation variables with the Actions button displayed in Figure 9-22. (If you need a refresher on the Actions button, see Chapter 6.)

As you fine-tune your plans in Project, you might find times when you simply need to use the Actions button to make a quick adjustment to Project’s response to a schedule change. Other times, you might want to change a task type to more consistently control how Project handles its scheduling.

To view or change a task type

1. Select the name of the task whose task type you want to change. The task must be automatically scheduled; task types do not apply to manually scheduled tasks.

2. On the Task tab, in the Properties group, select Information.

3. In the Task Information dialog, select the Advanced tab.

4. In the Task type field, do either of the following:

   • Note the current task type.

   • Select the new task type that you want.

     Tip

     If desired, you can modify the effort-driven setting along with the task type in this dialog. To confirm your choice, be sure to select the checkbox until it is empty (with Effort driven off) or checked (with Effort driven on). As a reminder, this setting can be changed only for fixed units and fixed-duration task types.

5. Select OK to close the Task Information dialog.

See task schedule details by using the Task Inspector

The Task Inspector succinctly reveals the scheduling factors that affect the selected task, as Figure 9-23 shows. These factors include predecessor task relationships, resource calendars, task calendars, or a combination of factors. In some cases, the Task Inspector includes options to resolve schedule issues such as resource overallocation. You resolve resource overallocations in Chapter 12.

For example, consider a task, Proof and review (task 22), whose predecessor is task 20, Cover design. The Inspector shows that Project has proposed two actions to resolve the resource overallocation: Move task to resources’ next available time and View overallocated resources in Team Planner.

You can select items recommended in the Inspector that have a hyperlink to get details about those items. For example, you can select the assigned resource’s name under Calendars to see that resource’s calendar. You don’t need to use the Task Inspector to change task details, but it can be a handy tool.

To display schedule details of a task with the Task Inspector

1. Display a task-centric view such as a Gantt chart view.

2. On the Task tab, in the Tasks group, select Inspect to open the Inspector pane.

3. Select a task. In the Inspector you can view the scheduling factors that affect the selected task.

Skills review

In this chapter, you learned how to

• See task relationships by using Task Path

• Adjust task link relationships

• Control task scheduling by using constraints

• Interrupt work on a task

• Adjust working time for individual tasks

• Control task scheduling by using task types

• See task schedule details by using the Task Inspector

Practice tasks

The practice files for these tasks are located in the ProjectDesktopSBSCh09 folder. For practice file download instructions, see the introduction to this book.