Triple Constraints & Task Dependency

Project Management


The discipline of organizing and managing resources (e.g. people) in such a way that the project is completed within defined scope, quality, time and cost constraints.

The application of knowledge, skills, tools and techniques to project activities to meet project requirements.

Traditional Triple Constraints

Time: The time to complete the project reflected in your project schedule.

Money: The project budget, based on the cost of the resources: the people, equipments, materials required to do the tasks.

Scope: The goals and tasks of the project and the work required to complete them.

Task – Definition

Task is an activity that has a beginning and an ending.

Each task is scheduled using the formula

Duration = Work / Resource effort (Units)

Work = Duration * Units

Fixed Work

Work is fixed & changes in Duration & Units does not affect the work to be done.

Fixed Duration

Total span of active working time (Start to finish of a task, as defined by the project & resource calendar) required for completing a task.

Fixed Units

Assigned units (resources) is a fixed value irrespective of changes in work or duration.

Task Dependency

Duration = Work / Resource effort

Duration is the actual amount of time that passes before the task is done.

Work is the effort required over a period of time to do the task.

Resource effort is the amount of effort resources are assigned to the task and their allocation.

For example, if:

Three painters work two days on a task, with an effort of 8 hours per day, the work for each resource is 16 hours: (2 days * 8 hours)

The total effort of the resources is 24 hours per day: (3 painters * 8 hours)

The total work for the task is 48 hours: (2 days * 8 hours * 3 painters)

The duration is 2 days: 48 hours / (3 painters * 8 hours)

Understanding this formula is important to understanding how changes you make to tasks affect the project schedule.

Task Dependency [Predecessor]

Finish-to-Start(FS)

Task (B) cannot start until Task (A) finishes

Finish-to Finish(FF)

Task (B) cannot finish until Task (A) finishes

Start-to-Start(SS)

Task (B) cannot start until Task (A) starts

Start-to-Finish(SF)

Task (B) cannot finish until Task (A) starts.