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D.1.1 Overview

This appendix gives examples of BNF representations of abstract message definitions at the segment level for HL7, version 2.2. It does not specify the field-level or data-type definitions nor does it define the message exchange protocol. It is not the only possible set of BNF productions capable of describing these messages, since the choice of tokens for certain segments and messages is to some extent arbitrary (e.g., should the EVN segment have a single token, or many?), as are the forms used to define recursion.

In the definitions that follow an attempt has been made both to follow the general use of message definitions given in the various chapters and to resolve questions of ambiguity.

For more information on BNF, see Compiler Design in C ; Allen I. Holub; Prentice Hall; Englewood Cliffs, New Jersey; 1990.

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