An Apex application is represented by a DAG, which expresses processing logic as operators (vertices) and streams (edges). Streams are unbounded sequences of pieces of data, also called events or tuples. The logic that can be executed is arranged in the DAG in sequence or in parallel.
The resulting graph must be acyclic, meaning that any given tuple is processed only once by an operator. An exception to this is iterative processing, also supported by Apex, whereby the output of an operator becomes the input of a predecessor (or upstream operator), introducing a loop in the graph as far as the streams are concerned. ...
