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Hour 4. Starting the Scheduling Process > Understanding How Tasks are Scheduled

Understanding How Tasks are Scheduled

As soon as you enter a new task in your project, Microsoft Project immediately places it on the schedule calendar. Exactly where it gets placed depends on whether your project is scheduled from a fixed start date or from a fixed finish date. These and the other factors controlling the scheduling of tasks are in the following list, which includes several new terms. They will be defined more precisely in the extended coverage for each factor—in most cases, later in this hour.

  • Tasks are usually scheduled to start as soon as possible, which means as soon after the start of the project as the other factors listed here will allow. (You learned how to set the start date for the project in the previous hour.) If your project is scheduled from a fixed finish date, tasks are scheduled to finish as late as possible, which means as close to the end of the project as possible. For example, if you start a new project file and give the project a fixed start date of January 8, 2001 (see Figure 4.1), then as you add tasks they are all initially scheduled to start as soon as possible after January 8, 2001.

  • Microsoft Project includes a built-in calendar that defines working days and nonworking days (such as weekends and holidays). The calendar also defines the times of day when work can be scheduled. For the most part, tasks are scheduled only during the working times defined in the calendar. The Gantt Chart shades the nonworking days in the timeline area. As you can see in Figure 4.4, if you select a start date for your project that falls on a Saturday, Project schedules tasks to start on the following Monday, the first working day after the start of the project. Similarly, if you entered a time of day for the start of your project that is not a working hour on the calendar, Project would schedule tasks to begin in the first working hour thereafter. You will see more about working times in this hour.

    Figure 4.4. Tasks are scheduled only on working days.

  • Some tasks take longer to complete than others, and you give Project that information by your entry in the Duration field. When you first create a task, Project assigns a default duration of one day, and schedules the finish date at the end of one full working day. If you later enter a different duration estimate for the task, Project reschedules the finish date. If, however, your project has a fixed finish date then Project would not adjust the finish date, but would move the start date to an earlier time period.

    In Figure 4.5, the duration estimates for the project have been entered. Some task bars are longer, others are shorter, and the task finish dates reflect the duration values.

    Figure 4.5. Adding duration estimates to tasks causes Project to adjust their scheduled dates.

  • Normally, Project assumes that once work begins on a task, it continues uninterrupted (except for nonworking days) until the task is finished. However, you can introduce arbitrary splits that interrupt the scheduled work on a task. In other words, you can schedule a task to start, stop, and start again at intervals of your choosing, and as often as you choose. For example, if an employee is unavailable or a piece of equipment breaks down (hopefully not vice versa), you could interrupt the task schedule until a replacement is available. In Figure 4.5, Task 13 shows a split that was introduced because the person doing that task will be away at a conference during that time.

  • If there is a fixed date defined for the individual task, it overrides Project's attempt to schedule the task as soon or as late as possible. For example, in the project in Figure 4.5, the start date for Meet with bankers (Task 9) has been fixed at January 15, 2001, because the business plan created in Task 7 won't be finished until that date. After you add this fixed date constraint to the Task, its scheduled start date shifts to the fixed date. Using constraints is covered in Hour 7, "Working with Deadlines and Constraints."

  • Most of the time, the start or finish of a task is dependent on the start or finish of some other task. For example, in a residential construction project, the start of the Frame Walls task must wait until the finish of the Prepare Foundation task. You define this dependency in Project by linking tasks. In Figure 4.6, Task 18 (Assemble first batch) is linked to Task 4 (Test prototype) and should not be started until Task 4 is finished; you shouldn't attempt to start assembling your new product until the prototype testing is successfully completed. Linking tasks is covered in Hour 6, "Linking Tasks in the Correct Sequence."

    Figure 4.6. The appropriate sequence for working on tasks is defined by linking tasks.

  • When you assign resources to work on tasks, it can affect the schedule in a number of ways. Changing the number of people or machines assigned to a task can affect the task's duration and, therefore, the task's finish date. For example, if you double the number of people working on a task, it usually means the task is finished more quickly. The availability of the resources also affects the schedule for the task; work must be scheduled around vacations and other nonworking times for the resources, which could lengthen the schedule for the task. And, if the same resource is assigned to two overlapping tasks, you might have to delay the work on one task while the resource works on the other task. Resource assignments are covered in Hours 11, "Defining Resources and Costs," 12, "Mastering Resource Scheduling in Microsoft Project," and 13, "Assigning Resources and Costs to Tasks."



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