The Triple Constraints
There were soon problems as people had different definitions of the “quality" side of the triangle. Dr. Barnes recognized that and attempted to redefine the triangle as “cost/time/performance." There was resistance to adopting this model as the more popular version “cost/time/scope" was beginning to take shape.
This is considered the classic project management triangle.
The amount of time it takes to complete a project is the time (schedule) leg of the triangle. The overall budget is the cost leg. The scope constraint is all of the work that must be completed to satisfy the project requirements.
When working with the triangle, it is initially drawn as an equilateral triangle where all sides are the same length. When using the graphic to communicate things that impact the project, one can show that anything that increases one constraint leg will impact the length of the other sides of the triangle.
Ideally, the equilateral triangle represents a project at its initial baseline state. Often, the word “quality" is written in the middle of the triangle. The initial triangle represents the concept that when all of the known cost, time and scope constraints are working together, the desired project quality will be achieved.
As the project moves forward, and sometimes before it even gets started, changes in the three constraints will occur, impacting the other two constraints. The customer increases the scope which generally means an increase in cost and time. An acceleration of the schedule (time) may result in an increase in costs and a reduction in scope. A reduction in the budget (cost) may require reducing the scope and extending the schedule (time).
Each of these impacts are easily communicated by redrawing the triangle to reflect the changes.
The value of using a graphic such as the project management triangle is in communicating the complexity of a project and the impact of various changes. While the concepts remain the same, the graphic has changed to meet the needs of the project manager to present the project status and facilitate discussions.
Variations of the classic project management triangle have been created to focus on unique projects and their challenges.