Chuck Boeheim, of the Stanford Linear Accelerator, is the author of a wonderful program called PIPEDEMO, which "animates" a pipeline to illustrate the flow of data from stage to stage.
To use PIPEDEMO, you simply write a normal pipeline specification but change PIPE commands to PIPEDEMO and change CALLPIPE commands to REXX PDCALL. Running a few CMS Pipelines examples through PIPEDEMO is an excellent way to get a deeper understanding of how pipelines work. PIPEDEMO can also be a big help in understanding why one of your pipelines is not working. PIPEDEMO is itself a pipeline, of course, and is well worth reading as an example of skillful use of CMS Pipelines.
PIPEDEMO is currently supported by Christian Reichetzeder C.Reichetzeder@AKH-Wien.AC.AT.