Project Management Scheduling Techniques

The methods used by project management software to schedule dates and times for tasks (and the resources assigned to them) are ingenious. You will need to understand the general concepts if you are to use Microsoft Project effectively. However, you don't need to master the details of how calculations are made. Although the applications of these methods are reviewed as needed in upcoming chapters, gaining an overview can be useful before you get into the details of planning and coordinating a project.

You Must Provide the Raw Data

You must provide accurate task information in order for Microsoft Project to calculate a schedule for a project. This usually requires a lot of guesswork, but without it, Project won't be as helpful to you. The less time you take in putting together reasonable task information, the less likely the computer projections will be reasonable. Start entering the data by following these steps:

• Enter a list of all the tasks that must be scheduled in order to complete the project. You must include either the duration of each task (how long it should take to do the work) or the total hours of work that the task requires. When this is combined with the resources you assign to the task, Project can calculate the work (if you estimate duration) or the duration (if you estimate the work).

• Include as milestones any major turning points in the project, such as the end of a major phase or a point where new decision making is called for.

• You must include any sequencing requirements (that is, dependencies) that will govern when the task can be scheduled. A sequencing requirement is a requirement that the scheduled date for a task has to be tied to the scheduled date for some other task. When you build a house, for example, you schedule the carpenters to start erecting the walls after the foundation has been finished. You link the date for starting the walls to the date when the foundation is scheduled to be finished.

• If a task must start or finish by a specific date, enter this requirement as a constraint on the scheduling of the task. For example, you might stipulate that a certain task can't start until the third fiscal quarter, due to cash-flow problems. Or, you might have a contract that requires that a task be finished by a specific date. When calculating a schedule of dates for tasks, Microsoft Project normally schedules each task to begin as soon as possible, considering the task's position in the sequence of tasks. However, Project takes note of your constraints and warns you if the schedule doesn't allow constraints to be met.

The Calendar Used for Scheduling

Microsoft Project uses its internal standard calendar to calculate a schedule for the tasks you enter. The default standard calendar has no holidays and assumes that work can be scheduled eight hours a day, from 8:00 a.m. to 5:00 p.m., Monday through Friday, with one hour for lunch . You must customize the standard calendar to make it represent the workdays and shifts of your organization. This standard calendar is used to schedule all tasks that do not have resources assigned to them.

How Project Calculates the Schedule

Project starts calculating a schedule when you enter the first task. With each added detail, the schedule is updated. The primary method used in project management software for scheduling is called the Critical Path Method (CPM). CPM calculates the overall duration of a project by chaining tasks together in their required sequences and then summing up the combined duration of all tasks in the chain.

Figure 1.2 illustrates a simple project that contains six tasks and a Project Finish milestone task. Tasks A, B, and C must be performed in sequence; Tasks X, Y, and Z must also be performed in sequence. Both sequences can occur at the same time; however, both sequences must finish in order for the project to be complete.

Figure 1.2. The longest sequence of tasks (the critical path) determines the finish date for the project.

If parallel task sequences are in progress at the same time, the overall duration of the project is the duration of the longest of these task sequences. In Figure 1.2, the sequence A-B-C takes 11 days, and the sequence X-Y-Z takes 9 days. Therefore, it takes 11 days to complete the project because this is the duration of the longest sequence.

You cannot complete the project on schedule unless the tasks on the longest sequence are finished on schedule. These tasks, known as critical tasks , are vital to keeping the overall project on schedule. A sequence of critical tasks is called a critical path . All tasks on the critical path must be finished on time as scheduled, or the finish date for the project will slip.

In Figure 1.2, Tasks A, B, and C are critical tasks, and the sequence A-B-C is the critical path. Tasks X, Y, and Z are not critical to finishing the project on time. You could delay the completion of any one of these tasks for up to two days without causing a delay of the overall project. The X, Y, and Z noncritical tasks are therefore said to have slack .

Critical tasks do not have slack. These tasks cannot be delayed if the project is to finish on schedule. So, having zero slack is one way to identify or define a critical task.

Why Should You Care About the Critical Path?

Identifying the critical tasks is an important time saver in managing a project. Suppose you need to shorten the duration of the overall project (sometimes called crashing the schedule ), and you're looking at the list of tasks to find some that you can finish more quickly than planned. (For example, you might add more resources to a task to finish its work sooner, or you might reduce the scope of a task or the quality of the work so that it takes less time to complete.) You don't have to look at each and every task in the project to find potential time savings; you can safely limit your analysis to ways to shorten the critical tasks and not worry about shortening the noncritical tasks. That's because reducing the duration of noncritical tasks would have no effect on the finish date. This knowledge can save you a great deal of time in trying to find ways to shorten a project's schedule.

How Resource Assignments Affect the Schedule

When you assign resources to tasks, the calculated schedule can change dramatically. Every resource has its own scheduling calendar, which shows when the resource is not available (such as maintenance downtime or vacations ) or when the resource is available in addition to the standard nonworking times for the organization. The project's base calendar is used to calculate schedules for tasks that have no resources assigned to them. When a resource is assigned, the task schedule changes to reflect the availability of the resource.

Changing the number of resources assigned to a task also affects its schedule. Some tasks have a fixed duration : No matter how many workers or resources you assign to the task, the duration remains unchanged. If you scheduled a task to deliver a small package to a customer in an outlying suburb, for example, you would assign a driver and a truck. You probably couldn't shorten the duration of the task by placing two drivers in the truck. In that case, the task would have a fixed duration. If, however, the task were to deliver a truckload of packages, a second driver could reduce the time it takes to load and unload the packages and thus reduce the duration of the task. If changing the number of resources assigned to a task leads to a change in the duration of the task, the task's duration is said to be resource driven (also called effort driven ). The schedule for the task is driven or determined by the number of resources assigned to the task.

Microsoft Project assumes that tasks are effort driventhat is, that they are not fixed-duration tasks. If a task has a fixed duration, you must define the task explicitly as fixed duration because Project assumes that you can shorten the duration of a task if you increase the resources assigned to do the work.