Difference between AFPDS and IPDS

Back in the old days (system 36) I used a subroutine subr50
to create IPDS files on the system 36, 38 and AS400
for creating forms and adding graphics to spooled files.

At some point IBM introduced AFP into the midrange world,
and now there are many references to IPDS and AFPDS
and sometimes these terms are interchanged (incorrectly). I
speak to many clients that reference AFP spooled files as
IPDS spooled files and visa versa. 
IPDS and AFP are not the exact same thing.
There are printers that support IPDS and AFP data streams
There are printers that support APFDS data streams but do
not support IPDS data streams.
On the CRTPRTF command you can specify either *AFPDS or
*IPDS.
Some times a printer device description is configured as
Advanced Function Printing *Yes sometime *NO and many times
they will both work sometimes this will cause problems
printing
 
I was asked more then once what is the difference and I
always struggle to explain to a client what the exact
difference is. 
I have had customers that wanted to convert their "AFP"
spooled files to PDF and the program they were using would
not convert them. Come to find out their "AFP" spooled files
were actually IPDS spooled files, changing them to AFP
spooled files (Advanced Function Printing = *YES) and they
convert fine.

My belief has been that IPDS exists only for backward
compatibility and most if not all new software would be
written using AFPDS rather then IPDS except that there are
some programmers that do not understand the difference and
that they should be specifying AFPDS. 

My questions:
1) Does anyone have a good definition of the difference
between AFPDS and IPDS?
2) When should IPDS be used instead of AFPDS to create
printer devices and spooled files?


Allen