Internal and External Dependencies are two kinds of logical relationships between two or more tasks that belong to either the same project or several different projects. Internal dependency means that tasks are dependent on each other within one and the same project. External dependency assumes that tasks of different projects or sub-projects are dependent on each other.
Internal dependency is used in those projects in which activities and tasks identify the amount of work to be done. In such projects their tasks logically relate to each other and never refer to non-related activities of other projects. Internally dependent tasks are performed and managed under the rules and conditions defined in their projects only. They are never subordinated to other, external projects and activities.
External dependency is often used either in one project that includes several sub-projects, or in multiple different projects. External dependency means that two or more tasks from different projects or sub-projects are dependent on each other. Such tasks may use common resources but have different goals, and vise-versa.