Saturday, March 1, 2008

Controlling Project Schedules

Another input to project schedule control is the project schedule. Project schedules are a set of planned dates for performing activities and meeting project milestones.

Project schedules are not considered complete until they have been approved. The approved schedule is known as the schedule baseline. A schedule baseline is a fixed project schedule that is the standard by which project performance is measured.

The schedule baseline is only adjusted when the project's scope has been significantly altered as, for example, when the project scope has changed.

When baselining a schedule, you need to consider project activities, dependencies, estimates, constraints, assigned resources, and resource availability.
  • Activities - Before baselining a schedule, it must be as complete as possible with regard to identifying all of the project's activities. If you overlook an activity, the schedule may need to be altered in order to add the activity later.
  • Dependencies - Network logic must be included in the schedule. Dependencies from other projects should also be considered. If, for example, you plan to start Project C on March 1st, but the resources will not be available until Project B is complete, this dependency must be built into the schedule.
  • Estimates - Estimates for activity duration and work effort must be reasonable. If you allot only 60 hours for a 100-hour activity in an attempt to cut costs, you are setting an unreasonable estimate which will affect the effectiveness of your entire schedule.
  • Constraints - All known constraints must be accounted for. If an employee needed to complete the project is only available for three months, you must account for this constraint in the schedule and make every effort to utilize this resource within the time he is available.
  • Assigned resources - Resources must be assigned to activities in a realistic manner, for example allowing for vacations and down-time. Resource requirements must be reviewed and compared to known capacity.
  • Resource availability - The scheduled dates must take resource availability into account, which means the schedule must be leveled manually or automatically. If you know that a supplier can only deliver its resources at the end of phase one, you should not schedule the activity until then.
The schedule can be baselined and used to measure project progress once you have carefully considered these project schedule inputs. Then with a baselined schedule in hand, you can begin the process of deciding which method to use to present the project schedule data.
Tom, the new project manager for Askme Consulting, is beginning his first project: constructing a new office complex in Manhattan. He is reviewing the work breakdown structure developed in the initial planning and estimating stage of the project proposal. Tom and his management team meet to determine the most appropriate method of presenting the schedule for this extensive project. The team needs to determine the types of information required when reporting the project's progress and predicting its future.

The methods they are considering are: the milestone chart, project network diagram (PND), time-scaled network diagram, and Gantt chart. The method they choose will depend on the variables they need to monitor and control as the project progresses.
  • A milestone chart is a summary-level schedule identifying the major activities or deliverables of the project. It can become the skeleton for the master schedule. A milestone typically marks the end of an event or the completion of an activity. For example, the first milestone activity for the Askme Consulting project is architecture/design. The second milestone activity is the foundation work.
  • A project network diagram (PND) is a schematic display of the project's activities and the logical relationship between them.
  • A time-scaled network diagram is a variation of the PND. The positioning and length of the activity represent its duration.
  • A Gantt chart is a graphic display of schedule-related information. A typical Gantt chart displays activities, dates, and durations. Gantt charts are the most convenient, commonly used, and easily understandable method of data presentation for project planning, resource scheduling, and status reporting.
Once you are familiar with the various methods of displaying project schedule data, you can use the information for conducting performance analysis. The Critical Path Method (CPM) plays a vital role in this analysis process. Critical Path (CP) is a series of activities that determines the earliest possible completion date for the project.
CP is the longest full path in the project. CP activities have little or no float. As activities are completed, the critical path may be altered. The CP can be determined for the entire project, a milestone activity or a sub-project.

The CPM is used to predict project duration by analyzing which sequence of activities or path has the least amount of scheduling flexibility or float. The early start and finish dates for each activity appear above the node on a Project Network Diagram. The late start and finish dates for each activity are below the node.

Early dates are calculated by means of a forward pass using a specified start date. Late dates are calculated by doing a backward pass, starting from a specified completion date. The most effective way to ascertain the critical path is to perform a forward and then a backward pass through the project.

To perform a forward pass, look at the first activity and determine its earliest possible start date. This is called early start. Continue this process for every activity.

To perform a backward pass, start at the last activity and determine the latest each activity can start without affecting subsequent activity. This is called late start.

Once you have completed the forward and backward passes, you must examine the results. If early and late start dates for an activity are the same, the activity is on the critical path. If there is a difference between the dates, the activity has float time and can be placed on the non-critical path.

Project schedules help you plan dates for performing activities and meeting project milestones. Schedule baselines and critical paths are important aspects of the schedule because they help in project schedule control. Together, these project scheduling tools and methods help project managers to monitor and measure project progress.

No comments: