Thank you, Robert Cemper.

In fact, I now do something like your line of inline sql: I retrive my messages from the general EnsLib.HL7.Message database using their id. Although I liked the idea of setting up my own table, I suspect this is not how the system is intended to be used.

I surely did not want to mess with The Enslib message class. The documentation also hinted to some (can't judge if dirty) tricks to do this, but I'd rather not risk crashing the whole system...

Instead of subclassing I now use routing of messages by means of their values (message type, certain textual data) to distinguish different messages.

I hope this works out. What is COS, by the way?