Duplicate Transmissions

Discussion: How should an HL7 Application (this is NOT a Messaging Infrastructure question) react to a duplicate Interaction ? For the purpose of this discussion, a duplicate interaction is defined as an interaction with one and the same Transmission.id as an interaction that has already been processed and responded to.

There are 2 basic options: HL7 either does or doesn't prescribe how systems should deal with duplicate transmissions. If HL7 prescribe the behaviour there are 3 ways of dealing with the duplicate transmission:

• Ignore it.
  • Simply ignoring a duplicate won't work at the HL7 layer, for we have a sending system that may be waiting for a response. It may have resend the message because (for one reason or other) it didn't receive a response.
• Reject it.
  • Rejecing a duplicate won't work at the HL7 layer, for we have a sending system that may be waiting for a response. It may have resent the message because (for one reason or other) it didn't receive a response. Sending a "reject" to the duplicate is better than just ignoring the duplicate, but doesn't really help the sender, other than to inform the sender that it should create a NEW interaction (different Transmission.ID) with the same contents.
• Send the same response (if any) as has been sent for the original interaction.
  • This fully satisfies the requirements of the sending system, but puts a burden on the recieving system, for it has to keep a record of all interactions it has sent.
  • For the Dutch implementation guide we wrote some quite complicated rules:
    • If the duplicate interaction has no receiver responsibilities, ignore it at the receivers end.
    • If the duplicate interaction has receiver responsibilities, then you need to respond with a duplicate of the response interaction as has been sent by the receiver when it originally received the interaction.
    • In order to detect duplicates and be able to send duplicate responses we now require that all systems have a 48-hour log of all messages sent/received. Maybe we need a shorter timeframe than 48 hours, time will tell.

Discussion

• Do we want HL7 to prescribe the way to deal with it ? No one size fits all solution.
• Does the way to deal with duplicates depend on message infrastructure used ? – No, that just affects the amount of lost messages.
• What is a valid reason to resend with the same message.id ? – should one always use a new Message.id on a resend ?
  • Replay messages obviously contains duplicate message.ids.
  • From sender perspective: no application response [although one was expected], what should a sender do ?
• Do we need a “this is a duplicate of message x” attribute ?

Business Process Duplicates

• Detection of duplicate order (via business ID) is different from a duplicate Transmission (message.id). How do we want to deal with this?