Dr. Goldratt’s theory of constraint (TOC) stresses systematic project management by identifying the unpredictable elements impeding project completion and offers global resource allocation [1–3]. The notion of thinking globally and acting locally suggests using global safety time and reducing activity length. However, there is no real strategy for reducing activity time and exerting managerial control. The critical chain [4], when combined with the project buffer and the activity buffer, causes various issues that must be addressed.
Gantt chart, Critical Path Method (CPM), and Project Evaluation and Review Technique are three prominent project scheduling methodologies (PERT). Gantt charts or bar charts are typically used to display project progress, and they frequently include information such as activity listings, activity length, schedule dates, and progress-to-date. It is useful since they are simple to comprehend and modify. They are the most basic and least complex way of depicting progress and can be quickly expanded to indicate particular issues. However, there are significant disadvantages to using a bar chart. For starters, Gantt charts do not depict the interdependence of operations. The link between activities is critical for controlling project costs; Gantt charts have limited predictive power without this relationship. Second, the Gantt chart cannot depict the outcome of an early or late start inactivity. Finally, Gantt charts do not depict the uncertainty involved in executing the activity and hence cannot be subjected to sensitivity analysis [5].
The fundamental purpose of a CPM study of a project is to identify the critical path, which defines the project’s minimal completion time. Forward and backward pass processes are used in the computing analysis. The forward pass finds the earliest start time and earliest completion time for each network activity, whereas the backward pass calculates the latest start time and latest completion time for each activity. Each activity is expected to begin at its earliest start time during the forward pass computation. In other words, a new action can begin as soon as the previous one is completed. The completion of the forward pass establishes the project’s earliest completion date. The converse of the forward pass analysis is the backward pass analysis. The project begins at the most recent completion time and ends at the most recent start time of the first activity in the project network. Because critical route tasks have no float time, limited resources must be given to the first to minimize project delays [5].
By introducing variability in activity length into the project network, the project assessment and review approach may be thought of as an extension of CPM. As a result, the possible variability in activity length is taken into account by employing three time estimations for each activity. The PERT formulae are based on a simplification of the mean and variance expressions of a beta distribution. The mean is approximated by a simple weighted average of the three time estimations, with the end points considered to be equally likely and the mode four times as likely [5].
Theory of Constraint
TOC schedules the project using global safety time and emphasizes that a system must have a restriction. Otherwise, without the upper bound, its production would rise. As a result, TOC put the emphasis on the constraint that prevents the project from achieving its goals. The following five stages are utilized to apply the TOC expertise to project scheduling [6–10].
- Identify the project constraint.
- Exploit the project constraint.
- Subordinate everything else to the project constraint.
- Elevate the project constraint, and
- If, in the previous step, a new constraint has been uncovered, repeat the process
Several concerns must also be carefully controlled in order to effectively use the improved TOC approach to the project scheduling challenge. These are as follows:
- To avoid project delays due to unknown circumstances, all project members should be made aware of the project purpose and their personal responsibilities.
- Use specialized subcontractors to avoid novice technical concerns and concentrate on project control challenges.
- Use the learning curve effect to minimise activity time and project length [11].
- Analyze the utilisation efficiency of each resource and activity performance to ease the project control choice [11,12], but keep in mind the disparities about the project and activity flexible coefficients.
- Appropriate time-cost trade-off [13,14].
- Prepare a contingency plan by doing a risk analysis
References
[1] Lee RK. Project management—the theory of constraints way training course. 1997.
[2] Goldratt EM. What is the thing called theory of constraint and
how should it be implemented. North River Press, Inc., 1990.
[3] Goldratt EM. Critical chain. North River Press, Inc., 1997.
[4] O¨ zdamar L, Ulusoy G. A local constraint based analysis approach to project scheduling under general resource constraints. European Journal of Operational Research 1994;79:287–98.
[5] Weia, C.-C., Liub, P.-H., & Tsaic, Y.-C. (2002 ). Resource-constrained project management using enhanced. International Journal of Project Management 20, 561–567.
[6] Goldrat EM. The theory of constraints. North River Press, Inc., 1986.
[7] Goldratt EM. TOC approach for Harris, Video Tape. 1995.
[8] Verma R. Management science, theory of constraints/optimized production technology and local optimization. Omega 1997;25: 189–200.
[9] Gardiner SC, Blackstone JH. The evolution of theory of constraints. Industrial Management 1994:5–6.
[10] Gardiner SC, Blackstone JH. Dynamic buffering. International Journal of Production Research 1998;2:333–42.
[11] Kurtulus J, Davis EW. Multi-project scheduling: categorization
of heuristic rules performance. Management Science 1982;28: 161–72.
[12] Morse LC, McIntosh JO, Whitehouse GE. Using combinations of heuristics to schedule activities of constrained multiple resource project. Project Management Journal 1996:34–40.
[13] Amor J-P, Teplitz C. An efficient approximation for project composite learning curves. Project Management Journal 1998:28–42.
[14] Johnson RV. Resource constrained scheduling capabilities of commercial project management software. Project Management Journal 1992;XXII:39–43.
