A processor is a unit of processing.  It has a clearly defined role in the system as a whole.

An object is a lump of data that the processor may act upon.

The nodes of a processor are linked to objects.

Interface to a processor:
	Most processors have a fixed number of named singular nodes.  Some processors may have named lists of nodes, bags of nodes or hashes of nodes.

A processor is a very high-level concept.  Each processor has many modes of operation.  Which one is used in a particular circumstance depends on:
	* the types of objects input and to be output
	* which nodes are incoming, which are outgoing

A processor is capable of more than simple action.  It also can propogate flow-control signals - 'pushes' and 'pulls' - through the network.  When a node is pushed, there no object is actually input.  What happens is that the processor tries to establish a pathway for objects to travel, if they are input on that port.  In a half-duplex channel, this 'push' is a request for control of the channel.

node states:
	closed | neutral | pulled | pushed | pulling | pushing | full

BEADS TIED TO STRINGS / CONVEYOR BELT MODEL