The Segment Grammar allows you to define the segments that a particular message consists of and how they should be grouped. This is the external format of the message as it is received or sent from other applications. An example of a message's segment grammar is shown below:

MSH
PID
OBR
OBX

Each segment contains information of a specific type. For example, using the above example:

• MSH contains information about the sender and receiver of the message, the type of message, etc.
• PID contains information about the patient such as their name, address, etc.
• OBR contains information about the observation request such as the physical examination or assessment.
• OBX contains information about the observation results.