PERT/CPM

Introduction

The reticular analysis enables design and planning of a project, at all levels of details, regarding the duration of each activity, the order of priority, the review of the program when changes or delays happen and finally the cost of the project.

The methods of reticular analysis which are used to optimize the design and planning of a project are PERT and CPM. These methodologies were developed independently of each other in late 50s. Researchers have used PERT method for handling problems with stochastic activities times while they have used CPM method for problems with deterministic times.

Essentially, this difference resulted because these two methods encountered problems of different nature during the period they were developed. There were also differences in the way in which the two methods depicting activities with a network form.

In PERT networks, the activities were represented with edges while in CPM networks the nodes symbolized the activities.

In any case, these differences do not exist anymore. The way of representation of the activities is based on the user selection while the methodology is merged in a common method which is called PERT/CPM method. According to this, all the networks which are obtained by this method, they are called PERT/CPM networks.

Usage

Discussion

The key questions that can be answered and moreover the general the information which can be acquired by the project manager and by extension, the execution group by constructing the PERT/CPM network are the followings:

• The graphical representation of the activities and in particular, accurate graphical representation of the sequence of prerequisite activities.
• The estimation of the total time that the work will last.
• The identification of the critical activities. In other words, all these activities that must not be delayed because then, the completion of the project will be delayed.
• The identification of non-critical activities. In other words, all these activities which have delay margins without affecting the project.
• For each non-critical activity, the slack time can be detected. In other words, this is the maximum possible margin delay of an activity without charge of the total time of the project.
• The identification of the probability of the project completion within a certain period of time and in particular in cases where the duration times of activities are estimations.
• The ability to monitor the temporal evolution of the project, the allocation of resources and the possibility of revising the program by changing times, identifying new critical activities and reallocating resources.
• The definition of the possibility to reduce the project completion time (crashing), by the determination of the required resources and the activities which need to be fed.