The trigger events build a link from HL7 transactions to the real world. Circumstances are described, in which a certain transaction is initiated. There is a many to one relation between trigger events and message types. Especially the ADT message is a superset of many messages which are though syntactically similar, distinct in their contents and purpose.
There is a classification of trigger events in the table of trigger event codes. However, there are more trigger events than are listed in the table 0003. From the view of the HL7 data base, the concept of event type codes is unfortunately degraded to merely a table of subselectors, which are defined only for those events, for which there is a many to one relation to message types. It is desirable to have a complete list of event codes, so that a message would be uniquely referred to by it's event code.
Until then we have to either refer to a message by specifying the message type and the event code (if there is one), or we have to merge the tables of message types and event codes into one such that any message type that has several event codes is removed from the merged table.