Todavía usas un diagrama de Gantt

Gantt (Bar) Charts and Microsoft Project® (MSP) One of the oldest but still one of the most useful methods of presenting project schedule information is the Gantt chart, developed around 1917 by Henry L. Gantt, a pioneer in the field of scientific management. The Gantt chart shows planned and actual progress for a number of tasks displayed as bars against a horizontal time scale. It is a particularly effective and easy-to-read method of indicating the actual current status for each of a set of tasks compared to the planned progress for each item of the set. As a result, the Gantt chart can be helpful in expediting, sequencing, and reallocating resources among tasks, as well as in the valuable but mundane job of keeping track of how things are going. In addition, the charts usually contain a number of special symbols to designate or highlight items of special concern to the situation being charted. Although the 3rd edition of PMBOK now calls these "bar charts," we will continue calling them Gantt charts here. There are several advantages to the use of Gantt charts. First, even though they may contain a great deal of information, they are easily understood. While they do require frequent updating (as does any scheduling/control device), they are easy to maintain as long as task requirements are not changed or major alterations of the schedule are not made. Gantt charts provide a picture of the current state of a project. Gantt charts, however, have a serious weakness. If a project is complex with a large set of activities, it may be very difficult to follow multiple activity paths through the project. Gantt charts are powerful devices for communicating to senior management, but networks are usually more helpful in the hands-on task of managing the project. Another significant feature of Gantt charts is that they are as easy to construct as a network. We use the example in the previous subsection to demonstrate how to construct such a chart. As is true of many things, it is important for the student to be able to understand just what it is that networks and Gantt charts show (and what they do not show) before using MSP or other software to draw complex networks and Gantt charts that the student will have to understand and use. Drawing networks and charts by hand is a quick way to develop that understanding. Once understanding is gained, however, software is easier, faster, and given a project of a size that reflects reality, far more cost effective. Consider the example in Figure 8-7 that was just used to illustrate how to draw a network. If we open MSP we see the form that is used to enter action plan (or WBS) data into the program. (You may have to close the MSP help box to see the whole form.) Entering the data is straightforward. We begin by entering an activity named "START." We assign it a duration of 0 days which makes it a "milestone" rather than a true "activity." We now enter activity a with a duration of five days, and then continue with the rest of the activities. At the end of the list, we add FINISH with zero days duration, the project ending milestone. The software automatically assigns a WBS (ID) number to each activity as you enter it. You may delete or add columns if you wish. If you do not enter a specific start date, the MSP will default to the present date for its start date. As you enter data from the action plan, MSP will draw an AON network and a Gantt chart automatically. (The Gantt chart will be visible to the right of the action plan information.) If the activity names and durations are entered without noting the appropriate predecessor information, all activities will be assumed to start on the same start date. As the predecessor information is entered, the proper relationships between the activities are shown; see Figures 8-11 and 8-12. Figure 8-11: MSP plan and Gantt chart for sample project in Figure 8-4. Figure 8-12: An MSP PDM/CPM network for sample project in Figure 8-4. Our concern so far has simply been to show the technological dependencies in a network or Gantt chart. A glance at the AON network or the Gantt chart shows something interesting. If we sum up the activity times for all activities in the action plan, we see that there are 30 days of work to schedule. But, as the network and chart show, the project is scheduled to start on January 21, 2002 and will be completed on February 14, 2002. That is 25 days, not 30. Further, MSP defaults to a work calendar with a five-day week. (Note that Saturday and Sunday are lightly shaded on the Gantt chart to indicate they are nonwork days.) If the calendar is adjusted to a seven-day week, the project will require only 19 days to be completed. It can be finished as early as February 8. Calculation of project duration has not yet been discussed, though it will be very shortly. Calculation-by-hand is not at all difficult, but MSP can do it faster and easier. It is important, however, to remember that software makes assumptions about such things as the number of days worked in a week, the number of hours per day that are worked, and several other matters that will be considered later. These assumptions may be changed if one wishes, but they must be considered every time the software is used to map a project. This example illustrates both the strength and weakness of the Gantt chart. Its major strength is that it is easy to read. All popular project management software will prepare Gantt charts, and most have some options available for customization. On balance, ease of construction and ease of use have made the Gantt chart the most popular method for displaying a project schedule. Nonetheless, a PDM/ADM network is still most useful for the PM to exercise control over the schedule, and the viewer may be misled if the Gantt chart is not read carefully or if it does not contain all appropriate information (Wilkens, 1997). In many ways, the Gantt chart is similar to the project master schedule described in Chapter 5. Both are types of bar charts and are used similarly. The major difference is that the Gantt chart is intended to monitor the detailed progress of work, whereas the master schedule contains only major tasks and is oriented toward overall project management rather than precise control of the detailed aspects of the project.