At this point, your tasks all have what you hope are realistic durations. What is not realistic is that the tasks might look like they’re all starting on the project start date. (See Figure 6-6.)
Figure 6-6. Until you enter task dependencies, start dates, or finish dates, all tasks appear to start on the project start date.
Although many tasks in a project are likely to begin on the project start date, most other tasks cannot begin until another task has finished. Sometimes, several tasks are dependent upon the completion of one task; sometimes, several tasks must finish before a single later task can begin.
So, the next step in creating your schedule is to link tasks that are dependent on each other. You can link the previous, or predecessor task, to its succeeding, or successor task, and thereby set up the task dependency between the two.
When your task dependencies are combined with your durations, your project plan starts to look like a real schedule. You can begin to see possible start dates and finish dates not only for the individual tasks, but also for major phases, milestones, and the project as a whole. When you create a link between two tasks, Project 2010 calculates the successor’s start and finish dates based on the predecessor’s start or finish date, the dependency type, the successor’s duration, and any associated resource assignments. There’s still more information and refinement to be done, but you’re getting closer to a schedule that starts to reflect reality.
The most typical link is the finish-to-start task dependency. With this link, the predecessor task must finish before the successor task can begin. To link tasks with the finish-to-start task dependency, follow these steps:
Display the Gantt Chart.
You can set task dependencies in any task sheet, but you can see the effects of the links immediately in the Gantt Chart.
In the task sheet, select the two tasks you want to link. Drag from the predecessor to the successor task if they are right next to each other. If they are not adjacent tasks, click the predecessor, hold down the Ctrl key, and then click the successor.
On the Task tab, in the Schedule group, click Link Tasks.
The tasks are linked in the chart area of the Gantt Chart as shown in Figure 6-7. In addition, the Predecessor field of the successor task lists the task number for its predecessor.
Note
When you edit the scheduling of a task—for example, its duration or a task dependency—you might affect other tasks that are linked with a task dependency to this task. When this happens, by default the changed cells are temporarily filled with a background color so that you can immediately see how your edit changed the scheduling for other tasks. This change highlighting changes or disappears when you make the next scheduling edit.
Note
For more information about change highlighting, see Highlighting the Ripple Effects of Schedule Changes.
Inside Out: Link in or out of order
When you drag across a series of tasks and then click Link Tasks, the tasks are linked in order from the task higher in the task list (lower Task ID number) to the task lower in the task list (higher Task ID number). It doesn’t matter whether you drag from top to bottom or bottom to top—the resulting links are the same. This is also true if you select adjacent tasks using the Shift key—the order of selection does not matter.
However, if you hold down Ctrl and click each task, the tasks are linked in precisely the order in which you select each individual task. Using this method, you can make a task lower in the list the predecessor of a task higher in the list.
Although the finish-to-start task dependency is the most common, there are four types of dependencies that help you model your task relationships. These dependency types are as follows:
Finish-to-Start (FS). As soon as the predecessor task finishes, the successor task can start.
Finish-to-Finish (FF). As soon as the predecessor task finishes, the successor task can finish.
Start-to-Start (SS). As soon as the predecessor task starts, the successor task can start.
Start-to-Finish (SF). As soon as the predecessor task starts, the successor task can finish. This type of link is rarely used, but still available if you need it.
Note
By default, when you move a task from one location to another in your task sheet or when you insert a new task, that task is automatically linked like its surrounding tasks. You can control this behavior. On the File tab, click Options, and then click Schedule in the left pane. Under Scheduling Options For This Project, select or clear the check box labeled Autolink Inserted Or Moved Tasks.
You’ve already seen that to quickly apply a Finish-To-Start task dependency, all you have to do is select the tasks in the task sheet, and then click the Link Tasks button. But what about applying one of the other types of task dependencies?
You can still work directly in the Gantt Chart—you just need to take it one step further. After linking the tasks, double-click the task link line in the chart area of the Gantt Chart. The Task Dependency dialog box appears, as shown in Figure 6-8. In the Type box, change the dependency type, and then click OK.
Figure 6-8. Double-click the task link line to open the Task Dependency dialog box and change the dependency type.
An alternative, which doesn’t require such a steady hand with the mouse, is to change the task dependency by using the Task Information dialog box. To do this, follow these steps:
Display the Gantt Chart or other task sheet view.
Link the tasks using the Link Tasks button as usual.
Click anywhere in the row for the successor task for the linked pair whose link type you want to change.
On the Task tab, in the Properties group, click Information.
You can also simply double-click the successor task to open the Task Information dialog box.
Click the Predecessors tab.
The Task Name field shows the name of the predecessor task to the current task, and the Type field shows that it’s a finish-to-start (FS) link.
Click in the Type field, and then click the arrow that appears in the field.
The four link types are listed in the drop-down menu that appears, as shown in Figure 6-9.
Click the link type you want, and then click OK.
The link between the Gantt bars is redrawn to reflect the new link type, and the notation in the Predecessors field is also updated.
Note
Not only can you link tasks within one project, you can link tasks in different projects. For more information, see Chapter 16.
Suppose that you have a pair of tasks with a finish-to-start link. Then you realize that the successor really can’t start when the predecessor is finished—there needs to be some additional delay. This is usually the case when something needs to happen between the two tasks that isn’t another task.
For example, suppose the “Order equipment” task is the predecessor to the “Install equipment” task. Although the equipment cannot be installed until after the equipment is ordered, it still cannot be installed immediately after ordering. Some lag time is needed to allow for the equipment to be shipped and delivered. In such a case, the successor needs to be delayed. You can enter lag time in the schedule to accurately reflect this condition.
Lag time can be expressed as a percentage of the predecessor; for example, 75%, or as a specific time period; for example, 16h or 3ed.
To enter lag time for a linked task, follow these steps:
Display the Gantt Chart or other view with a task sheet.
Select the successor task that is to have the lag time.
On the Task tab, in the Properties group, click Information.
In the Task Information dialog box, click the Predecessors tab.
In the Lag field for the existing predecessor, type the amount of lag time you want for the successor. Use a positive number, and enter the lag time as a percentage or duration amount.
One way to make your project schedule more efficient is to overlap linked tasks where possible. Suppose you have a task that isn’t scheduled to begin until a previous task is finished. You realize that the predecessor doesn’t actually have to be finished—the successor can really begin when the predecessor is only 50 percent complete. The successor essentially gets a 50-percent head start, hence the term lead time. For example, “Construct walls” is the predecessor to “Plaster walls.” Although plastering cannot be done until the walls are constructed, the final wall does not need to be constructed before plastering of the first wall can begin. You can set an amount of lead time for the “Plaster walls” task.
Lead time is expressed as a negative value. If you think of it as reducing time in the schedule, the minus sign makes sense. Lead time can be expressed as a percentage of the predecessor; for example, -25%, or as a specific time period; for example, -4d or -1ew.
To enter lead time for a linked task, follow these steps:
Display the Gantt Chart or other view with a task sheet.
Select the successor task that is to have the lead time.
On the Task tab, in the Properties group, click Information.
In the Task Information dialog box, click the Predecessors tab.
In the Lag field for the existing predecessor, type the amount of lead time you want for the successor. Use a negative number, and enter the lead time as a percentage or duration amount.
Note
Although it might seem strange to use the Lag field to enter lead time, “lag time” and “lead time” are essentially the same idea. They express the amount of time that should pass before the successor task should start (or finish). Lag time adds time between the performance of predecessor and successor tasks, so it is expressed as a positive number. Lead time subtracts time between the performance of predecessor and successor tasks, hence the negative number.
To remove all predecessor and successor links on a task, follow these steps:
In any task view, click the task.
On the Task tab, in the Schedule group, click Unlink Tasks.
All predecessor and successor links to and from the selected task are removed.
To change or remove an existing task dependency by using the link line in the chart area of the Gantt Chart, follow these steps:
Display the Gantt Chart or other Gantt view.
In the chart area of the Gantt view, double-click the link line representing the link you want to change or remove.
In the Task Dependency dialog box, use the Type or Lag box to make the changes you want.
If you want to remove the link altogether, in the Type box, click None.
To change or remove an existing task dependency by using the Task Information dialog box, follow these steps:
Display the Gantt Chart or other view with a task sheet.
Select the successor task whose link you want to change.
On the Task tab, in the Properties group, click Information.
In the Task Information dialog box, click the Predecessors tab.
Click in the Type field for the predecessor you want to change, and then select the type of task dependency you want it to be: Finish-to-Start (FS), Start-to-Start (SS), Finish-to-Finish (FF), Start-to- Finish (SF), or None. If you select None, the link is removed entirely.
Caution
Removing a link from a task can move the scheduling of the task back to the project start date. Always check the new start and finish dates on a task when you have removed a link or changed the link type to be sure that the task is scheduled the way you expect.
Note
As with setting dependency types or entering lead or lag time, you can use the Predecessors field in the sheet area of the Gantt Chart to change or remove a link.
Note
To undo recent edits, click Undo on the Quick Access Toolbar in the upper-left corner of the Project 2010 window. Each time you click Undo, the previous edit is undone in the reverse order in which it was performed. You can also press Ctrl+Z to undo edits.
To redo an edit that you’ve undone, click Redo on the Quick Access Toolbar. You can also press Ctrl+Y.
When more details are needed, the following views can give you a closer look at the task dependencies in your project:
The Gantt Chart shows task dependencies with link lines between the Gantt bars. In fact, all Gantt views show task dependencies this way.
The Network Diagram shows each task as an individual node with link lines between them. The Descriptive Network Diagram shows the same view, but the nodes are larger and provide more detail.
The Relationship Diagram shows the predecessors and successors of a single selected task. This view is particularly useful for a large project or any project with complex linking.
The Task Details Form, Task Form, and Task Name Form can show predecessors and successors of a single selected task as part of a combination view. For example, you can display the Gantt Chart in the upper pane, and one of the task forms in the lower pane. In fact, the Task Entry view is the built-in combination view of Gantt Chart and Task Form. By default, these forms show assigned resource information in the left grid, and the predecessor information in the right grid. To show predecessor and successor information in the form, first click the form pane and then on the Format tab, in the Details group, click Predecessors & Successors.
