As you can see at this link, the ASAE Data Standards Committee has released a preliminary set of standards for constituent XML. According to the site,

"For those who understand XML standards, the various documents will be self-explanatory. For those not used to dealing with these types of documents, this document should provide at least a place to start as the documents are reviewed."

This work is incredibly important to making all of our lives easier when it comes to integrating multiple systems. Please review the page and the included documents and comment on them. Note that you need not be an ASAE member to comment.