activityonnode

Activity on Node (AON) is a project network diagram technique used in critical path method (CPM) scheduling. In AON, each node represents a single activity, typically labeled with the task name and its duration. Directed edges connect nodes to show precedence relations, where an edge from a predecessor to a successor indicates that the successor cannot start until the predecessor finishes. The resulting network encodes the sequence constraints of a project and serves as the basis for timing calculations.

AON is often contrasted with Activity on Arrow (AOA), where activities are depicted as arrows and events as nodes. In AOA, complex dependencies sometimes require dummy activities to maintain logic. Because AON places durations directly on the activity nodes, it is generally regarded as more intuitive and easier to read for many planners, especially in complex projects.

Construction and analysis of an AON network typically involve: listing activities with their durations and immediate predecessors, drawing a network of nodes and directed connections, and performing forward and backward passes to determine early start, early finish, late start, and late finish for each activity. From these values, slack or float is computed, and the critical path—composed of activities with zero slack—is identified. The critical path determines the minimum project duration and highlights activities that require close management.

Applications of AON span construction, manufacturing, software development, and other projects requiring clear visualization of task sequencing. Limitations include the assumption of fixed activity durations and dependencies, and potential complexity in very large projects where additional techniques or tools may be used to manage resources and uncertainties.