Guide to HL7 V2 message parsing and management of character escaping with reference to backward compatibility

This technical report describes HL7 V2 message parsing and management of character-escaping with reference to backward compatibility.

HL7 V2 was created before XML was developed. As a result, HL7 V2 established its own encoding formats to allow complex hierarchical data structured to be encoded into text strings. It was also designed to allow backward and forward compatibility. Unlike XML, it does not add the field names to the message, and prior out-of-band metadata is required to read the values in the message. This makes it less readable by humans (compared with XML) but results in very small messages and is highly efficient. It requires careful parser implementation to use this format.

This report brings together the relevant information into one document to allow high-quality implementation of HL7 V2 parsers.

Main sections:

· Scope

· HL7 message encoding

· HL7 message structure

· Segments

· Datatypes

· Parsing HL7 V2

· Dealing with reserved characters and delimiters

· Free text formatting

· Unicode characters