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Back  RFI # 1995: How do I read the BNF product?

Formal vs. Informal Help Informal Formal


Robert Sailors


I see in X12.6 Section Relational Conditions that there is a production:
<segment_unit_position_in_segment> ::= <digit> | <digit>
I would read this like "the position in the segment is a digit or a digit." This appears at least redundant. It implies to me that positions are single digits.

Relational conditions seem to be published in the X12 documents using two digits left-padded with zero. I expected to see
<segment_unit_position_in_segment> ::= <digit><digit>

There is a similar issue with the production for component_element_position_in_composite that immediately follows this.

Submitter Assigned Keywords

BNF Relational


Thank you for submitting this request. Your expectation regarding the segment definition "<segment_unit_position_in_segment>::=<digit> | <digit>" is correct. The pipe symbol appears to be erroneously introduced after version 5010. It will be corrected at the next available opportunity.
Submission 12/3/2014
Status Date 6/9/2015
Status F - Final
Primary References
Document X12.6