Health Level 7, set of international standards
Old version 2.x (non-XML):
MSH header segment
PID Patient identity
PV1 patient visit information
Tilde ~ default repetition separator
Caret ^ component separator
Pipe | field separator
Ampersand & for subcomponent separator
ADT-A01 message type and triggerm used when a patient is admitted
OBR
MSH (header) contains the type and trigger information
ACK is the expected response after system receives an HL7 message (as opposed to NACK?)