Hi Thomas,
do I understand you correctly that you would like to write your own implementation to communicate with the UIM message bus?
Can you let me know what use case you are trying to implement?
We are always considering which APIs/SDKs are needed for the product and this might be a good input for us.
To come back to your initial question: There is no public facing documentation about the structure of PDS messages as far as I know. As you know, CA offers SDKs in various languages to abstract the exact structure of PDS for you.
best regards
Chris