A flow is a sequence of steps. Steps have a main input and a main output, but for ‘Create’ flows the first step does not have a main input part. This is shown schematically in the following figure:

In the figure the first flow is a flow that creates parts. This means that at the moment the flow starts and enters the first step, the user has to specify the number of parts that need to be created. From that moment on the parts will exist in the system.

The flow that ‘Grabs’ the parts is not creating parts but transforming an existing Part A into a Part B.

Examples of flows that create parts are flows that put parts into inventory. If there is no order flow, or any other preceding flow, these flows have to create the parts in the system. From there on the parts will live their lives and the system will always keep a record and a history for these parts.

In general most of the flows in the system will grab parts that already exist in the system. An exception could be Assembly Flows.