- The use of (often implicit) resource dependencies. Implicit means that they are not included in the project network but have to be identified by looking at the resource requirements.
- Lack of search for an optimum solution. This means that a “good enough” solution is enough because:
- As far as is known, there is no analytical method of finding an absolute optimum (i.e. having the overall shortest critical chain).
- The inherent uncertainty in estimates is much greater than the difference between the optimum and near-optimum (“good enough” solutions).
- The identification and insertion of buffers:
- project buffer
- feeding buffers
- resource buffers.
- Monitoring project progress and health by monitoring the consumption rate of the buffers rather than individual task performance to schedule.
Critical Chain Overview (CCPM)
Critical Chain Project Management (CCPM) is a method of planning and managing projects that puts the main emphasis on the resources required to execute project tasks. It was developed by Eliyahu M. Goldratt. This is in contrast to the more traditional Critical Path and PERT methods, which emphasize task order and rigid scheduling. A Critical Chain project network will tend to keep the resources levelly loaded, but will require them to be flexible in their start times and to quickly switch between tasks and task chains to keep the whole project on schedule.
With traditional project management methods, 30% of the lost time and resources are typically consumed by wasteful techniques such as bad multi-tasking, Student syndrome, In-box delays, and lack of prioritization.
In project management, the critical chain is the sequence of both precedence- and resource-dependent terminal elements that prevents a project from being completed in a shorter time, given finite resources. If resources are always available in unlimited quantities, then a project’s critical chain is identical to its critical path.
CCPM aggregates the large amounts of safety time added to many subprojects in project buffers to protect due-date performance, and to avoid wasting this safety time through bad multitasking, student syndrome, Parkinson’s Law and poorly synchronized integration.
Critical chain project management uses buffer management instead of earned value management to assess the performance of a project. Some project managers feel that the earned value management technique is misleading, because it does not distinguish progress on the project constraint (i.e. on the critical chain) from progress on non-constraints (i.e. on other paths).