Pick List to Invoice Number translation

I'd like to build a process that creates a file of pick list numbers and their 
resulting invoice numbers.  In our environment, a pick list can contain lines 
from one or more orders.  A separate invoice is produced for each order on the 
pick list, once the pick is complete and confirmed.

I've looked at a program that can display the pick list associated with a given 
order and, essentially, I'd like to reverse the process.  Conceptually, it 
looks like I need to read selected WHP77 records to find the correct event 
number (EVNO77) associated with a pick list number (ACNO77).   Having obtained 
the event number, I should then be able to read INP57 using the event number to 
find the corresponding Customer Order number(s) and despatch note sequence 
number.  Finally, knowing that, I should be able to read OEP65 using Customer 
Order number and despatch note sequence number to obtain the corresponding 
invoice number.  

Assuming that's correct logic, my dilemma is how do I determine which WHP77 
records represent pick list "events"?

(Santa: can I have a book, for Christmas, that explains the S21 database, field 
meanings and how files are related?)!!

==Kevin Brunk
The Butler Company 


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