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2.4 HL7 MESSAGES

This section and sections 2.5 through 2.9 define the components of messages and provide the methodology for defining abstract messages that are used in later chapters. A message is the atomic unit of data transferred between systems. It is comprised of a group of segments in a defined sequence. Each message has a message type that defines its purpose. For example the ADT Message type is used to transmit portions of a patient’s ADT data from one system to another. A three character code contained within each message identifies its type. These are listed in the Message Type list, Appendix A.

The real-world event that initiates an exchange of messages is called a trigger event. (See Section 2.2.1, "Trigger events" for a more detailed description of trigger events.) Appendix A contains the codes that represent all defined trigger events. These codes represent values such as A patient is admitted or An order event occurred. There is a one-to-many relationship between message types and trigger event codes. The same trigger event code may not be associated with more than one message type; however a message type may be associated with more than one trigger event.

All message types and trigger event codes beginning with the letter "Z" are reserved for locally defined messages. No such codes will be defined within the HL7 Standard.

This section defines the components of messages and provides the methodology for defining abstract messages that is used in later chapters.

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