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What is a 'message'?
In health informatics, the term 'message' is used in a fairly specific way to mean a packet of information sent between two applications, containing predefined content. Historically messages have been defined by HL7, EDIFACT, ASTM and other standards organisations. Each message definition specifies the structure and contents for a particular transmission. Historically messages have been used for pharmacy orders, lab orders and results among other things. Messages have always been manually defined by groups of people within standards organisations. Semantically, they carry requests, replies, many of which are 'changes in state'. For example, an HL7v2 message is defined containing a blood film result in such a way that the complete result can be sent, or just one or two analytes, marked as corrections with respect to a previous message carrying the complete result. The same scheme is used for microbiology results, due to the culturing time and the need to generate intermediate results.