One implication of this idea is that Purchase and Sales Orders for dependent demands are unnecessary baggage. Similarly, Jeff Sutherland suggested that when a hospital patient is admitted, the diagnosis triggers many dependent requirements for tests, facilities, skills, etc. Another example is backflushed payments for components when the end item is sold. However, all of the example systems cited above have analogs to these objects, usually organized in roughly the same way. Petri nets are a form of finite state machine with places, transitions and tokens.
Transitions can fire when the required tokens inhabit the required places.
In the schema below, Stock Flows are places, Activities are transitions, Resources are tokens, and Events move the tokens from one place to another. Timed should be obvious. These are meant to illustrate the required granularity. The REA model considers all economic resources as subtypes with significant shared behavior. Conversion Transforming input Resources into output Resources.