History
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Critical sequence was originally identified in the 1960s.[ citation needed ]
Critical chain project management (CCPM) is a method of planning and managing projects that emphasizes the resources (people, equipment, physical space) required to execute project tasks. [1] It was developed by Eliyahu M. Goldratt. It differs from more traditional methods that derive from critical path and PERT algorithms, which emphasize task order and rigid scheduling. A critical chain project network strives to keep resources levelled, and requires that they be flexible in start times.
Critical chain project management is based on methods and algorithms derived from Theory of Constraints. The idea of CCPM was introduced in 1997 in Eliyahu M. Goldratt's book, Critical Chain. The application of CCPM has been credited with achieving projects 10% to 50% faster and/or cheaper than the traditional methods (i.e., CPM, PERT, Gantt, etc.) developed from 1910 to 1950s. [2]
According to studies of traditional project management methods by Standish Group and others as of 1998, only 44% of projects typically finish on time. Projects typically complete at 222% of the duration originally planned, 189% of the original budgeted cost, 70% of projects fall short of their planned scope (technical content delivered), and 30% are cancelled before completion. [3] CCPM tries to improve performance relative to these traditional statistics.
With traditional project management methods, 30% of lost time and resources are typically consumed by wasteful techniques such as bad multitasking (in particular task switching), student syndrome, Parkinson's law, in-box delays, and lack of prioritization. [4]
In a project plan, the critical chain is the sequence of both precedence- and resource-dependent tasks 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 method.
Critical chain is an alternative to critical path analysis. Main features that distinguish critical chain from critical path are:
CCPM planning aggregates the large amounts of safety time added to tasks within a project into the buffers—to protect the due-date performance and 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). Event chain methodology can determine the size of the project, feeding, and resource buffers.
A project plan or work breakdown structure (WBS) is created in much the same fashion as with critical path. The plan is worked backward from a completion date with each task starting as late as possible.
A duration is assigned to each task. Some software implementations add a second duration: one a "best guess," or 50% probability duration, and a second "safe" duration, which should have higher probability of completion (perhaps 90% or 95%, depending on the amount of risk that the organization can accept). Other software implementations go through the duration estimate of every task and remove a fixed percentage to be aggregated into the buffers.
Resources are assigned to each task, and the plan is resource leveled, using the aggressive durations. The longest sequence of resource-leveled tasks that lead from beginning to end of the project is then identified as the critical chain. The justification for using the 50% estimates is that half of the tasks will finish early and half will finish late, so that the variance over the course of the project should be zero. [5]
Recognizing that tasks are more likely to take more time than less time due to Parkinson's law, Student syndrome, or other reasons, CCPM uses "buffers" to monitor project schedule and financial performance. The "extra" duration of each task on the critical chain—the difference between the "safe" durations and the 50% durations—is gathered in a buffer at the end of the project. In the same way, buffers are gathered at the end of each sequence of tasks that feed into the critical chain. The date at the end of the project buffer is given to external stakeholders as the delivery date. Finally, a baseline is established, which enables financial monitoring of the project.
An alternate duration-estimation methodology uses probability-based quantification of duration using Monte Carlo simulation. In 1999, a researcher[ who? ] applied simulation to assess the impact of risks associated with each component of project work breakdown structure on project duration, cost and performance. Using Monte Carlo simulation, the project manager can apply different probabilities for various risk factors that affect a project component. The probability of occurrence can vary from 0% to 100% chance of occurrence. The impact of risk is entered into the simulation model along with the probability of occurrence. The number of iterations of Monte Carlo simulation depend on the tolerance level of error and provide a density graph illustrating the overall probability of risk impact on project outcome.
When the plan is complete and the project is ready to start, the project network is fixed and the buffers' sizes are "locked" (i.e., their planned duration may not be altered during the project), because they are used to monitor project schedule and financial performance.
With no slack in the duration of individual tasks, resources are encouraged to focus on the task at hand to complete it and hand it off to the next person or group. The objective here is to eliminate bad multitasking. This is done by providing priority information to all resources. The literature draws an analogy with a relay race. Each element on the project is encouraged to move as quickly as they can: when they are running their "leg" of the project, they should be focused on completing the assigned task as quickly as possible, with minimization of distractions and multitasking. In some case studies, actual batons are reportedly hung by the desks of people when they are working on critical chain tasks so that others know not to interrupt. The goal, here, is to overcome the tendency to delay work or to do extra work when there seems to be time. The CCPM literature contrasts this with "traditional" project management that monitors task start and completion dates. CCPM encourages people to move as quickly as possible, regardless of dates.
Because task duration has been planned at the 50% probability duration, there is pressure on resources to complete critical chain tasks as quickly as possible, overcoming student's syndrome and Parkinson's Law.
According to proponents, monitoring is, in some ways, the greatest advantage of the Critical Chain method. Because individual tasks vary in duration from the 50% estimate, there is no point in trying to force every task to complete "on time;" estimates can never be perfect. Instead, we monitor the buffers created during the planning stage. A fever chart or similar graph can be created and posted to show the consumption of buffer as a function of project completion. If the rate of buffer consumption is low, the project is on target. If the rate of consumption is such that there is likely to be little or no buffer at the end of the project, then corrective actions or recovery plans must be developed to recover the loss. When the buffer consumption rate exceeds some critical value (roughly: the rate where all of the buffer may be expected to be consumed before the end of the project, resulting in late completion), then those alternative plans need to be implemented.
| | This section needs expansion. You can help by adding to it. (April 2010) |
Critical sequence was originally identified in the 1960s.[ citation needed ]
Project management is the process of supervising the work of a team to achieve all project goals within the given constraints. This information is usually described in project documentation, created at the beginning of the development process. The primary constraints are scope, time and budget. The secondary challenge is to optimize the allocation of necessary inputs and apply them to meet pre-defined objectives.
A real-time operating system (RTOS) is an operating system (OS) for real-time computing applications that processes data and events that have critically defined time constraints. An RTOS is distinct from a time-sharing operating system, such as Unix, which manages the sharing of system resources with a scheduler, data buffers, or fixed task prioritization in multitasking or multiprogramming environments. All operations must verifiably complete within given time and resource constraints or else fail safe. Real-time operating systems are event-driven and preemptive, meaning the OS can monitor the relevant priority of competing tasks, and make changes to the task priority. Event-driven systems switch between tasks based on their priorities, while time-sharing systems switch the task based on clock interrupts.
Project planning is part of project management, which relates to the use of schedules such as Gantt charts to plan and subsequently report progress within the project environment. Project planning can be done manually or by the use of project management software.
Eliyahu Moshe Goldratt was an Israeli business management guru. He was the originator of the Optimized Production Technique, the Theory of Constraints (TOC), the Thinking Processes, Drum-Buffer-Rope, Critical Chain Project Management (CCPM) and other TOC derived tools.
The critical path method (CPM), or critical path analysis (CPA), is an algorithm for scheduling a set of project activities. A critical path is determined by identifying the longest stretch of dependent activities and measuring the time required to complete them from start to finish. It is commonly used in conjunction with the program evaluation and review technique (PERT).
The theory of constraints (TOC) is a management paradigm that views any manageable system as being limited in achieving more of its goals by a very small number of constraints. There is always at least one constraint, and TOC uses a focusing process to identify the constraint and restructure the rest of the organization around it. TOC adopts the common idiom "a chain is no stronger than its weakest link". That means that organizations and processes are vulnerable because the weakest person or part can always damage or break them, or at least adversely affect the outcome.
Project management software are computer programs that help plan, organize, and manage resources.
The program evaluation and review technique (PERT) is a statistical tool used in project management, which was designed to analyze and represent the tasks involved in completing a given project.
In project management, resources are required to carry out the project tasks. These can be people, equipment, facilities, funding, or anything else capable of definition required for the completion of a project activity. The lack of a resource can therefore be a constraint on the completion of the project activity. Resources may be storable or not storable. Storable resources remain available unless depleted by usage, and may be replenished by project tasks that produce them. Nonstorable resources must be renewed for each time period, even if not used in previous periods.
Project portfolio management (PPM) is the centralized management of the processes, methods, and technologies used by project managers and project management offices (PMOs) to analyze and collectively manage current or proposed projects based on numerous key characteristics. The objectives of PPM are to determine the optimal resource mix for delivery and to schedule activities to best achieve an organization's operational and financial goals, while honouring constraints imposed by customers, strategic objectives, or external real-world factors. Standards for Portfolio Management include Project Management Institute's framework for project portfolio management, Management of Portfolios by Office of Government Commerce and the PfM² Portfolio Management Methodology by the PM² Foundation.
Critical Chain is a novel by Dr. Eliyahu Goldratt using the critical chain theory of project management as the major theme. It is really a teaching method for the theory.
A schedule or a timetable, as a basic time-management tool, consists of a list of times at which possible tasks, events, or actions are intended to take place, or of a sequence of events in the chronological order in which such things are intended to take place. The process of creating a schedule — deciding how to order these tasks and how to commit resources between the variety of possible tasks — is called scheduling, and a person responsible for making a particular schedule may be called a scheduler. Making and following schedules is an ancient human activity.
The following outline is provided as an overview of and topical guide to business management:
Event chain methodology is a network analysis technique that is focused on identifying and managing events and relationships between them that affect project schedules. It is an uncertainty modeling schedule technique. Event chain methodology is an extension of quantitative project risk analysis with Monte Carlo simulations. It is the next advance beyond critical path method and critical chain project management. Event chain methodology tries to mitigate the effect of motivational and cognitive biases in estimating and scheduling. It improves accuracy of risk assessment and helps to generate more realistic risk adjusted project schedules.
A glossary of terms relating to project management and consulting.
The project management triangle is a model of the constraints of project management. While its origins are unclear, it has been used since at least the 1950s. It contends that:
The following outline is provided as an overview of and topical guide to project management:
Drag cost is a project management metric developed by Stephen Devaux as part of the Total Project Control (TPC) approach to project schedule and cost analysis. It is the amount by which a project's expected return on investment (ROI) is reduced due to the critical path drag of a specific critical path activity Task or other specific schedule factor such as a schedule lag or other delaying constraint.
Spider Project is a project management software, developed by a company, called Spider Project Team.