How should an HL7 grammar define repetition
- Eliot Muir
Analytics
Chameleon has a data model for defining repetition on segments which was a little redundant:
<message_grammar id="4">
<name>NK1</name>
<is_optional>True</is_optional>
<is_repeating>True</is_repeating>
<ignore_segment_order>True</ignore_segment_order>
<max_repeats>0</max_repeats>
<type>segment</type>
<segment_ref>2</segment_ref>
</message_grammar>Notice how we have True for “is_repeating” yet max_repeats is set to 0.
This a bit of a design problem in that we have a redundant data model - we are describing the same property in a two ways and we end up with a contradiction:
The is_repeating property is true - which means that we have repeating segment.
But the max_repeats is set to 0 which says that the segment is not repeating.
How can we describe the properties of optionality and repetition in a simplest model that we can with as little ambiguity as possible in our new schema model with only one node type?
What about
min - if this zero then it means the node is optional
max
0 has no meaning
-1 means no limit
N means N repeats
I wonder about the value of restricting the number of repeats since in practice having limits on the messaging format doesn’t get a lot of value - it’s just annoying if an HL7 parser rejects a message because it exceeds the number of repeats or has one less. What is we did this instead:
IsRequired -
true - means the field is required
IsRepeating
What about
IsOptional
Just means we can skip over it, but we’re not going to reject a message
IsRepeating