The reason that there are Paths is to carry Flows. In the case of Roadway Paths, the flow is of traffic—a number of vehicles per hour; in the case of Rivers or Canals, the flow is water; in the case of Power Lines the flow is of electricity.
In Figure 22-8, Flow is defined as a quantity of material (or energy) that passes through a Path during a specified period of time. Attributes of Flow include Start Date [and Time], End Date [and Time] and Quantity. The Quantity is in terms of a Unit of Measure.
Figure 22-8: Flows
Because there are many kinds of Flows that can pass through even the same kind of Path, Flow Type describes the kind of ...