アローダイアグラムArrow Diagram

Learn in the textbookScope and Schedule Management

DefinitionAn arrow diagram (アローダイアグラム) is a scheduling chart that draws activities as arrows and the points between them as circles, linking them to show the order of activities and their durations on one page.

ExplanationThe arrows are called activity arrows and the circles at their ends nodes (結合点); an activity leaving a node cannot start until every activity entering it has finished. The path from start to finish with the largest total of days is the critical path (クリティカルパス), and that total is the shortest possible duration of the whole project (13 days in the figure, via A→B→dummy→E). The dotted line is a dummy activity that makes E wait for B; it takes no days and only expresses the order between activities.

AnalogyThink of cooking dinner: while the rice cooks, you make the soup and grill the fish. The tasks run side by side, yet nothing reaches the table until the slowest of them is done.

Memory hookArrow versus bar: the arrow diagram is named after its arrows, and the Gantt chart is built from bars. Pair the two shape words, arrows for connections and bars for duration.

Learn in the textbookSchedule Planning and the Arrow Diagram

DefinitionAn arrow diagram (アローダイアグラム) shows tasks as arrows and the breaks between tasks as circles called nodes, setting out the order of tasks and their durations.

ExplanationEach arrow stands for one task, its direction shows the order, and the number beside it gives the duration. Nodes mark where tasks start and end. An arrow that carries no actual work and only expresses an ordering is a dummy activity, drawn as a dotted line with a duration of 0.

Memory hookThe name comes from the English word arrow. True to the name, tasks are drawn as the arrows, not as the circles.