Critical Path Method (CPM) and Critical Chain

Critical Path Method (CPM) and Critical Chain Method (CCM). How is CCM an improvement over CPM?

The Concepts

The concept of paths and the slacks on the path have been around the management circles from the 1960s, with the concept of slack being defined as the amount of time an activity on a production line can be halted without affecting the project completion date. (Hansen, 1964) Likewise the critical path and the critical management of work flow are not new concepts. However the way they come to be viewed are new. The project planning begins with the concept of what is to be achieved, how it will be achieved and the time and method that will be used in completing the project. There are many variables that are to be considered that include dependence is, slack and the work flow and allocation of work and the performance appraisal. It also involves analysis of the slack time, and the way the work has bottle necks or dependencies.

This network of diagrams is based on the activity and the critical time involved in the completion. The critical path method uses the network diagram to split up the work in terms of modules indicating the flow of work through the network and the duration. Thus there can be parallel activities through two paths that end in creating a unit of turnout, or independently proceed to the goal. There could be smaller paths that are interconnected such that the performance of one precedes the other. This is to be charted in a network diagram and the directions of work is estimated as it is perceived to progress such that the critical path has the entire work in chunks of time and the total sum of the work time makes the longest of the critical path -- between the beginning and the end. The making of the critical path plan is the first step to create synergy between the various participants and for anticipating resistance and delay. (Schwalbe, 2006)

The critical path method is a system that can be a graphical model of work flow with anticipation of the interdependencies. The critical path methods have representations in a graphic form that can be a map on paper of the actual method of allotting work and the process of work flow. The disadvantages are that the diagrams are mostly stipulated but not often pragmatic and there are issues where situations that are frequently encountered are clumsier to represent and the critical path suffers from the flaw of non-representations of these events. It thus cannot show the elimination of activities that may not be necessary or useful. It is useful in eliminating noon critical activities and keeping the unit to the critical activities. (Schwalbe, 2006)

The critical chain method incorporates the allocation of resources in the system and thus is superior than the critical path because of the reasons that in the critical chain method not only are the scheduled allotted as per the system of the critical path, with the schedules calculated from the end date backwards, and the path defined, but the resources that are needed for each of the units are also anticipated and mapped. In some cases the resources allocation forms the priority for completion of that particular schedule. (Hill, 2011) The critical chain method is only an addition to the critical path in the allocation of resources to a critical path and analysis of where the overuse of the resources exists and where the resources have been allotted in surplus. In that view it is not possible to have a critical chain view of things without first creating the critical path which would be core to the system analysis.

The critical chain management concept is based on the Theory of Constraints -- TOC to project management, also as Critical Chain Scheduling and Buffer Management -- CC/BM, has recently emerged as one of the most popular approaches to project management. Though the method is good, it has been noted by researchers that there are benchmark problems. It is found that the 50% buffer rule for resources required buffer may not be apt in many cases and there is a great need for updating the baseline schedule and the critical chain provides the best intermediate estimates of the final project duration and yields the smallest final project duration. (Herroelen; Leus, 2001)