Interrelationship of Activities
What is an Interrelationship of Activities and what different types exist?
The temporal, practical and temporal planning of activities
An interrelationship of activities defines the temporal, practical and logical relationship between two planning elements in a project, a plan, or a product development. Depending on the terminology used, planning elements can be activities, tasks, work packages, and so on. When defining relationships, two aspects must be taken into account:
- Binding and non-binding relationships. Binding relationships define a fixed point in time for an activity – sometimes as the start date, often as the completion date – or a factual or logical relationship. For example, software cannot be installed on a computer until it has been ordered and delivered by the purchasing department.
- External and internal relationships. In the case of external relationships, external specifications are made, for example, by customers or partners. The freedom in planning transactions is limited in comparison to the internal relationship.
Types of interrelationships between activities
There are basically four types of relationships that are used in Precedence diagrams or Gantt charts, for example:
- The normal sequence or Finish-to-Start relationship in which a successor activity begins when the predecessor activity has been completed. It is the most common in project management practice, hence the name “normal sequence”.
- The start sequence or Start-to-Start relationship where successors can start when the predecessor is started. The start sequence can – but does not have to – lead to parallel activities.
- The end sequence or Finish-to-Finish relationship in which a successor cannot be terminated until the predecessor has been terminated.
- The jump sequence or Start-to-Finish relationship in which a successor cannot be terminated until the predecessor has been started. The jump sequence is relatively rare in planning. Example: Invoicing cannot be completed until a computer has been shipped.