NACHA - the Electronic Payments Association - manages the development,
administration and governance of the ACH Network for electronic payments.
Payment
messages are defined by the ACH Record Format Specifications section of the NACHA Operating Rules
and Guidelines.
A NACHA message is referred to as a file, and consists of a File Header record, repeating batches and a File Control record. A batch consists of a Batch Header record, repeating entries and a Batch Control record. An entry consists of an Entry Detail record optionally followed by Addenda records.
DFDL schemas for NACHA 2013 are available on the 
GitHub DFDLSchemas web site.
Last updated Friday, 21 July 2017