Developing the Project Schedule

A project schedule includes the sequence of activities, the relationships between the activities, and the timing of each activity. There are two major tools used to schedule projects: Gantt Charts and networks, including PERT and CPM. Henry Gantt invented the chart that bears his name to present the sequence and time required for a project’s activities.

What the traditional Gantt Chart can’t show, however, is the relationship between activities. Some activities (called parallel activities) aren’t related at all. The pretest (refer to Figure 2.6) can be developed at the same time that travel arrangements are being made. Other activities can’t begin until another activity is partially or wholly completed. Activities that must occur before the current activity are its predecessors, and an activity and its predecessors are related in series. The relationship between activities directly influences the project timeline. Materials must be published before they can be duplicated, and they must be duplicated before they can be shipped; therefore, publishing and duplicating are predecessors of shipping. If the materials aren’t published at the time specified in the project schedule, duplicating and shipping might be delayed.

Project uses a modified Gantt Chart that includes links to show activity relationships, as shown in Figure 2.6. The link lines clearly indicate series and parallel relationships between the activities.

Figure 2.6: Project’s modified Gantt Chart shows activities and relationships.

While Project’s linking feature handles the shortcomings of the traditional Gantt Chart, there are two other methods you can use to schedule projects. These methods were developed long before the creation of Microsoft Project, or even microcomputers.

PERT (an acronym for Program Evaluation and Review Technique) and CPM (Critical Path Method ) are network-scheduling methods. PERT was created by the U.S. Navy to manage an ambitious project: building the first nuclear submarine. At nearly the same time, CPM was developed by Remington Rand Corporation’s J.E. Kelly and M.R. Walker of DuPont Corporation to manage maintenance projects in chemical manufacturing facilities. PERT is more mechanistic because it was designed with an emphasis on using mathematics to manage uncertainty. CPM was designed for a very certain environment. Over the past three decades, the two methods have been modified through continued use and are now quite similar.

Both PERT and CPM use network diagrams (also called precedence diagrams) to represent the relationships among activities. On a network diagram, each activity is represented by a separate network node.

One advantage of using Project is evident when you begin to schedule activities: Gantt Charts and network diagrams are easily created by simply switching to a different view. A Project network diagram for the first four tasks in the Gantt Chart (refer to Figure 2.6) is shown in Figure 2.7.

Figure 2.7: A network diagram is another way to view tasks and relationships.

Simple projects can be easily scheduled and managed with Gantt Charts. In Chapter 8, we’ll show you how to use Gantt Charts to schedule a project. For complex projects or projects with a great number of unknowns, we recommend PERT. PERT is more than a diagram; it’s a method to manage project uncertainty, and is a useful tool whenever you do anything innovative or risky.