Sub-projects are smaller, interrelated projects that compose larger projects. If sub-projects belong to one and the same project or programme, they are dependent upon each other in some way. Dependency between sub-projects is called inter-project dependency. This kind of dependency creates logical and time-based links between structural elements of broader projects, portfolios and programmes.
Inter-project dependency determines the behavior and subordination of sub-projects within a single project framework. It identifies type of relationships between sub-projects and rules their connectedness to the root project. The process of managing inter-project dependency consists of these steps:
- Define the root or parent project that will be decomposed into smaller sub-projects
- Identify key activities that cause the life-cycle of the root project
- Allocate one or more sub-projects to each of the key activities
- Establish goals for every sub-project
- Break down every sub-project into smaller measurable activities (tasks and sub-tasks)
- Assign goals to tasks of every sub-project
- Understand how tasks of one sub-project relate to tasks of other sub-project(s) (for example, through using risk-based decomposition approach or critical path method)
- Develop a project decomposition matrix that includes sub-projects with their dependencies
- Identify controls for managing sub-projects and their dependencies
- Set milestones for sub-projects to monitor their status and performance.