The Project Management Triangle (called also Triple Constraint) is a model of the constraints of project management

Project management

Project management is the discipline of planning, organizing, securing, and managing resources to achieve specific goals. A project is a temporary endeavor with a defined beginning and end , undertaken to meet unique goals and objectives, typically to bring about beneficial change or added value...

. It is often used to illustrate that project management success is measured by the project team's ability to manage the project, so that the expected results are produced while managing time and cost.

Overview

Like any human undertaking, projects need to be performed and delivered under certain constraints. Traditionally, these constraints have been listed as "scope

Scope (project management)

In project management, the term scope has two distinct uses: Project Scope and Product Scope.Project Scope"The work that needs to be accomplished to deliver a product, service, or result with the specified features and functions."Product Scope...

," "time," and "cost". These are also referred to as the "Project Management Triangle," (also known as the "Iron Triangle") where each side represents a constraint. One side of the triangle cannot be changed without affecting the others. A further refinement of the constraints separates product "quality" or "performance" from scope, and turns quality into a fourth constraint.

Dr. Martin Barnes created the 'project management triangle' in the 1970s. 45 years later, Barnes is still active in project management serving as President of APM

Association for Project Management

The Association for Project Management is a registered charity in the United Kingdom, which aims to develop and promote the professional disciplines of project management and programme management, through a programme called the "Five Dimensions of Professionalism"...

. He is also a founding member of the Association, an honorary fellow and past chairman Quoted from.

The time constraint refers to the amount of time available to complete a project. The cost constraint refers to the budgeted amount available for the project. The scope constraint refers to what must be done to produce the project's end result. These three constraints are often competing constraints: increased scope typically means increased time and increased cost, a tight time constraint could mean increased costs and reduced scope, and a tight budget could mean increased time and reduced scope.

The discipline of Project Management is about providing the tools and techniques that enable the project team (not just the project manager) to organize their work to meet these constraints.

Another approach to Project Management is to consider the three constraints as finance, time and human resources. If you need to finish a job in a shorter time, you can throw more people at the problem, which in turn will raise the cost of the project, unless by doing this task quicker we will reduce costs elsewhere in the project by an equal amount.

Time

For analytical purposes, the time required to produce a deliverable

Deliverable

Deliverable is a term used in project management to describe a tangible or intangible object produced as a result of the project that is intended to be delivered to a customer . A deliverable could be a report, a document, a server upgrade or any other building block of an overall project.A...

 is estimated using several techniques. One method is to identify tasks needed to produce the deliverables documented in a work breakdown structure

Work breakdown structure

A work breakdown structure , in project management and systems engineering, is a deliverable oriented decomposition of a project into smaller components. It defines and groups a project's discrete work elements in a way that helps organize and define the total work scope of the project.A work...

 or WBS

WBS

WBS may refer to:* WebChat Broadcasting System, a virtual community* Warwick Business School, the largest academic department of the University of Warwick* Ward-Beck Systems, Canadian manufacturer of Audio and Video equipment...

. The work effort for each task is estimated and those estimates are rolled up into the final deliverable estimate.

The tasks are also prioritized, dependencies between tasks are identified, and this information is documented in a project schedule. The dependencies between the tasks can affect the length of the overall project (dependency constrained), as can the availability of resources (resource constrained). Time is different from all other resources and cost categories.

According to PMBOK the Project Time Management processes include :

1. Activity Definition
2. Activity Sequencing
3. Activity Resource Estimating
4. Activity Duration Estimating
5. Schedule Development
6. Schedule Control

Activity Definition (detail)

1a. Activity Definition Inputs

Enterprise environmental factors, Organizational process assets, Project Scope statement, Work Breakdown Structure, WBS Dictionary, Project Management Plan

1b. Activity Definition Tools

Decomposition, Activity Templates, Rolling Wave Planning, Expert Judgment Collection, Planning Components

1c. Activity Definition Outputs

Activity list, Activity scope attributes, Milestones list, Change Requests

Activity Sequencing (detail)

2a. Activity Sequencing Inputs

Project Scope Statement, Activity List, Activity Attributes, Milestones List, Approved change requests

2b. Activity Sequencing Tools

Precedence Diagramming Method (PDM), Arrow Diagramming Method

Arrow Diagramming Method

An arrow diagramming method is a network diagramming technique in which activities are represented by arrows.It is used for scheduling activities in a project plan....

 (ADM), Schedule Network templates, Dependency degeneration, Applying leads and lags

2c. Activity Sequencing Outputs

Project Schedule Network diagrams, Activity List Updates, Activity Attributes Updates, Request Changes

Activity Resource Estimating (detail) :

3a. Activity Resource Estimating Inputs

Enterprise Environmental factoring, Organizational process assets, Activity list, Activity attributes, Resources Availability, Project Management Plan

3b. Activity Resource Estimating Tools

Expert Judgment Collections, Alternative Analysis, Publishing estimating data, Project management software implementation, Bottom up estimating

3c. Activity Resource Estimating Outputs

Activity resource requirements, Activity attributes, Resource breakdown structure, Resource calendars
Request change updates.

Activity Duration Estimating (detail):

4a. Activity Duration Estimating Inputs

Enterprise environmental factors, organization process assets, Project scope statement, activity list, activity attributes, activity resource requirements, resource calendars, project management plan, risk register, activity cost estimates

4b. Activity Duration Estimating Tools

Expert judgment collection, analogous estimating, parametric estimating, three point estimating, reserve analysis

4c. Activity Duration Estimating Outputs

Activity duration estimates, activity attribute updates and estimates

Schedule Development (detail):

5a. Schedule Development Inputs

Organizational process assets, Project scope Statement, Activity list, Activity attributes, project Schedule Network diagrams, Activity resource requirements, Resource calendars, Activity duration estimates, project management plan, risk register

5b. Schedule Development Tools

Schedule Network Analysis, Critical path method, schedule compression, what if scenario analysis, resources leveling, critical chain method, project management software , applying calendars, adjusting leads and lags, schedule model

5c. Schedule Development Outputs

Project schedule, Schedule model data, schedule baseline, resource requirements update, activity attributes, project calendar updates, request changes, project management plan updates, schedule management plan updates



Schedule Control (detail):

6a. Schedule Control Inputs

Schedule management plan, schedule baseline, performance reports, approved change requests

6b. Schedule Control Tools

Progressive elaboration reporting, schedule change control system, performance measurement, project management software, variance, analysis, schedule comparison bar charts

6c. Schedule Control Outputs

Schedule model data updates, schedule baseline. performance measurement, requested changes, recommended corrective actions, organizational process assets, activity list updates, activity attribute updates, project management plan updates

Due to the complex nature of the Process Group called 'Time' the unique project management credential PMI-SP (PMI Scheduling Professional) was created.

Cost

To develop an approximation of a project cost depends on several variables including: resources, work packages such as labor rates and mitigating or controlling influencing factors that create cost variances tools used in cost are, risk management

Risk management

Risk management is the identification, assessment, and prioritization of risks followed by coordinated and economical application of resources to minimize, monitor, and control the probability and/or impact of unfortunate events or to maximize the realization of opportunities...

, cost contingency

Cost contingency

When estimating the cost for a project, product or other item or investment, there is always uncertainty as to the precise content of all items in the estimate, how work will be performed, what work conditions will be like when the project is executed and so on. These uncertainties are risks to the...

), cost escalation

Cost escalation

Cost escalation is defined as changes in the cost or price of specific goods or services in a given economy over a period of time. This is a similar to the concepts of inflation and deflation except that escalation is specific to an item or class of items , it is often not primarily driven by...

, and indirect costs . But beyond this basic accounting approach to fixed and variable costs, the economic cost that must be considered includes worker skill and productivity which is calculated using various project cost estimate tools. This is important when companies hire temporary or contract employees or outsource work.

Cost Process Areas

• Cost Estimating is an approximation of the cost of all resources needed to complete activities.
• Cost budgeting aggregating the estimated costs of resources, work packages and activities to establish a cost baseline.
• Cost Control - factors that create cost fluctuation and variance can be influenced and controlled using various cost management tools.

Project Management Cost Estimating Tools

• Analogous Estimating

Using the cost of similar project to determine the cost of the current project

• Determining Resource Cost rates
  The cost of goods and labor by unit gathered through estimates or estimation.
• Bottom Up estimating
  Using the lowest level of work package detail and summarizing the cost associated with it. Then rolling it up to a higher level aimed and calculating the entire cost of the project.
• Parametric Estimating
  Measuring the statistical relationship between historical data and other variable or flow.
• Vendor Bid Analysis
  taking the average of several bids given by vendors for the project.
• Reserve Analysis
  Aggregate the cost of each activity on the network path then add a contingency or reserve to the end result of the analysis by a factor determined by the project manager.
• Cost of Quality Analysis
  Estimating the cost at the highest quality for each activity.

Project managers often use project management software

Project management software

Project management software is a term covering many types of software, including estimation and planning, scheduling, cost control and budget management, resource allocation, collaboration software, communication, quality management and documentation or administration systems, which are used to...

 to calculate the cost variances for a project.

Scope

Requirements specified to achieve the end result. The overall definition of what the project is supposed to accomplish, and a specific description of what the end result should be or accomplish. A major component of scope is the quality of the final product. The amount of time put into individual tasks determines the overall quality of the project. Some tasks may require a given amount of time to complete adequately, but given more time could be completed exceptionally. Over the course of a large project, quality can have a significant impact on time and cost (or vice versa).

Together, these three constraints have given rise to the phrase "On Time, On Spec, On Budget." In this case, the term "scope" is substituted with "spec(ification)."

Evolution of the Project Constraint Model

Traditionally the Project Constraint Model recognised three key constraints; "Cost", "Time" and "Scope". These constraints construct a triangle with geometric proportions illustrating the strong interdependent relationship between these factors. If there is a requirement to shift any one of these factors the at least one of the other factors must also be manipulated.
With mainstream acceptance of the Triangle Model, "Cost" and "Time" appear to be represented consistently. "Scope" however is often used interchangeably given the context of the triangle's illustration or the perception of the respective project. Scope / Goal / Product / Deliverable / Quality are all relatively similar and generic variation examples of this, while the above suggestion of 'People Resources' offers a more specialised interpretation.
This widespread use of variations implies a level of ambiguity carried by the nuance of the third constraint term and of course a level of value in the flexibility of the Triangle Model. This ambiguity allows blurred focus between a project's output and project's process, with the example terms above having potentially different impetus in the two contexts. Both "Cost" and "Time" represent the top level project's inputs.
The ‘Project Diamond’ model engenders this blurred focus through the inclusion of "Scope" and "Quality" separately as the ‘third’ constraint. While there is merit in the addition of "Quality" as a key constraining factor, acknowledging the increasing maturity of project management, this model still lacks clarity between output and process. The Diamond Model does not capture the analogy of the strong interrelation between points of the triangles however.
More recently the Project Management Book of Knowledge (PMBOK 4.0) offered an evolved model based on the triple constraint with 6 factors to be monitored and managed . This is illustrated as a 6 pointed Star that maintains the strength of the triangle analogy (two overlaid triangles), while at the same time represents the separation and relationship between project inputs/outputs factors on one triangle and the project processes factors on the other.
PMBOK 4.0 6 Point Star variables:

Triangle 1

• Scope
• Cost
• Time

Triangle 2

• Risk
• Quality
• Resources

When considering the ambiguity of the third constraint and the suggestions of the "Project Diamond"; it is possible to consider instead the Goal or Product of the project as the third constraint, being made up of the sub factors "Scope" and "Quality". In terms of a project's output both "Scope" and "Quality" can be adjusted resulting in an overall manipulation of the Goal/Product. This interpretation includes the four key factors in the original triangle inputs/outputs form. This can even be incorporated into the PMBOK Star illustrating that "Quality" in particular may be monitored separately in terms of project outputs and process. Further to this suggestion, the use of term "Goal" may best represent change initiative outputs, while Product may best represent more tangible outputs.