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Overview

The structure of an HL7 message is as follows:

Message --> Segments --> Composites --> Other composites or primitive data types.

You will encounter the generic term 'field' that will usually refer to either a whole composite or to a sub-field (single value). In this document, a whole composite is referred to as a field (...|DOE^JOHN^^^^MD|...) and a single value is referred to as a sub-field (...^JOHN^...).

Development Tip

If you decided to implement your HL7 connectivity without any tools, your HL7 parser will detect each field according to its number from the start of the appropriate segment. If you need a patient name, count five "|" (pipe) characters from the start of the PID segment:

PID||0475^^^2^ID1|45||DOE^JOHN^^^^MD|

You need to be careful about doing this since some vendors tend to omit a number of fields, especially in very long segments. Do not hard-code field numbers in your parser. In practice it may vary although it is strictly prohibited by the standard.

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