Predecessor and Successor are two types of dependent tasks that belong to one and the same project or process and that are performed under dependency rules. A predecessor task determines the start or finish date of its successor task.
Both types are available in any work breakdown structure that includes dependent activities. Dependency rules between tasks determine which of the tasks are predecessors and which ones are successors. Graphically it can be presented as a tree-like structure in which every higher level is the successor of its lower level, and vice-versa – every lower level is the predecessor of its higher level.
Essentially, dependency between tasks and sub-tasks is the predecessor-successor relationships. Such relationships are used in various project management methodologies. For example, CPPM (Critical Path Project Management) uses resource-based dependencies to identify predecessors and successors among tasks of critical path. PRINCE2 establishes the predecessor-successor relationships between project stages to ensure a smooth flow of project activities from one stage to another one.