Since HL7 messages are not bound to one specific transport protocol, it doesn't define a specific addressing scheme. Instead HL7 defines two fields per address the one called the Application and the other the Facility. Where not otherwise stated, we use these fields as follows:
Particularly we presume the notion that one facility has one or more applications. The example facility used here is `060_IOP' and applications are `ABL', `CVGATEWAY', `ADT', `CLI', and `TEST'. Other HL7 interfaces might interpret these data items differently, however, the interpretation used here corresponds at least to the interpretation used by the CareVue system.
Each message has a sending application/facility and a receiving application/facility. The fields are optional, even though addresses are essential to message routing. Since the routing problem is not yet generally addressed, neither here nor in HL7, and since ProtoGen applications use direct addressing (IP addresses, files or devices), the application/facility names do not have uniform functions.