IT is very important to have a schedule of the project. The schedule is a management tool that will be used by everyone involved in the project. Project scheduling entails making a logical sequence between the tasks and then calculating the start and stop dates for each task, which are displayed as a diagram. To schedule the tasks or work packages, the following factors must be known.

What previous work the subsequent work packages depends, i.e. the task dependencies
The estimated durations of the work packages
The available float for the work packages, i.e. whether the work package must be carried out within a certain period or whether the time period in which the work must be done can float between two extremes
The combination of this information is used to determine what can be done and when it can be done. There are a number of well-known techniques for modeling project work. These are the gant chart, the project evaluation and review technique (PERT) and the critical path method (CPM).

The Gant Chart
The Gant chart is a diagrametric representation of the project which plots the tasks, people responsible for the tasks and the timeline. The basic format of the gant chart consists of a listing of tasks on the left hand side, followed by the start date, number of days to complete and the finish date. Each task is assigned one or more owners. To the right of the text listing is a bar or graphical representation of the time or duration of the tasks. The Gant chart is easy to read, showing only one set of start and finish dates. It provides a visual means to check the status of a task and excellent for summarizing the progress of a related group of tasks. It is an excellent tool for reporting because of its simplicity, visual orientation and summarization capabilities.

The Gant chart has a serious drawback. It is very difficult to determine the impact of a slip on one task on the rest of the project. The reason is that the chart in its original form does not show the interdependencies of the tasks. Nowadays, software programs do show the links between bars, overcoming this limitation. The gant chart, when augmented by notations to show dependencies is easier to produce and update.

PERT
The PERT chart uses a connected series of nodes to make explicit dependencies between tasks. In addition, the order of the tasks is given by the flow of the connections from left to right. But the horizontal dimension is not necessarily linear in time. The time resources required are given numerically, rather than appearing graphically. With PERT, it is possible to calculate the probability that an activity will be completed by a certain period of time.

Critical Path Management (CPM)
The critical path management (CPM) is similar to the PERT but includes an explicit indication of the critical path. The critical path is the sequence of tasks that defines the minimum amount of time required to complete the project. A delay in any one of these tasks will cause the entire project to be delayed. The CPM chart makes these paths explicit. Otherwise, the CPM shares the same characteristics with PERT and they are now customarily lumped together as one technique.

Network Diagrams
The network diagrams are used to show the sequence in which the activities are performed. The main advantage of using either the CPM or PERT is that you can tell whether it is possible to meet an important project completion date and exactly when various tasks must be completed in order to meet that deadline. You can also tell which tasks have floats and which do not have floats.
Engr. Obumeyan is a Chartered Chemical Engineer and is presently engaged as Consultant on the Abuja Light Rail Project.