General information on FHIR Messaging

Messaging is a means of coupling applications in a loosely manner, similar to what is known from HL7 v2 messaging.

FHIR messaging is not yet specified in the same way as RESTful interactions are, especially the definition of events (i.e. the CodeSystem of message-events) and the definition of the message content (i.e. pre-defined messageDefinition) are not detailed out. This leaves a certain degree of freedom to the application developers implementing FHIR messaging and results in less plug-and-play interoperability than in the RESTful interaction part of the FHIR specification.

However, certain aspects are specified by the FHIR standard:

• The message being sent from a source application to a destination application is a Bundle of type “message”.
• Several resources are bundled in this message, the first is the MessageHeader, the others are business resources and depend on the type of message.
  • In the MessageHeader the event of the message is specified (in messageHeader.event). The associated valueSet is an example binding in FHIR R4.
  • The MessageDefinition resource specifies which other resources are communicated as part of the message.