The Control/Query chapter of this Standard defines the generic rules that apply to all messages. Subsequent sections define functionally specific messages to be exchanged among certain applications. The specific aspects of message definition that are addressed herein are:
a) the form to be used in functional chapters for describing messages. This includes their purpose, their contents, and the interrelationships among them. This form is called an abstract message definition because it is purely a level 7 (application) definition.
b) the HL7 encoding rules for converting an abstract message into a string of characters that comprise an actual message
c) the programming procedures required to exchange messages using the HL7 specifications
d) the anticipated relationship with lower level protocols
e) certain message segments that are components of all messages
f) a single message, the acknowledgment message, that may be used unchanged in multiple applications