First, lets list the HL7 delimiters taken from the CDC HL7 Version 2.5.1 Implementation Guide for Immunization Messaging: Delimiters: Delimiter characters are used to separate segments, fields and components in an HL7 message. The delimiter values are given in MSH-2 and used throughout the message. Applications must use agreed upon delimiters to parse the message. Messages used in this Guide SHALL use the following delimiters: <CR> = Segment Terminator; | = Field Separator; ^ = Component Separator; & = Sub-Component Separator; ~ = Repetition Separator; \ = Escape Character. Now lets look at an example using sample data: On line two in the above example notice how the HPath changes from PID-3[1].4 when the cursor is positioned on the first "GEHC" versus PID-3[2].4 when positioned on the second "GEHC" Because the tilde is the Repetition Separator, the instance for PID-3 is incremented from 1 to 2. I think this can be better explained by another example. In this example I simply removed the tilde ("~"). Which in this case doesn't makes sense but just to illustrate: Above results in a HPath of PID-3[1].8. Reading the HPath from right to left, lets compare the HPath for the second "GEHC", using the CDC specs: PID-3[2].4 = Get the forth (.4) component of the second ([2]) repetition of the third (-3) field in the first PID (PID) segment. PID-3[1].8 = Get the eighth (.8) component of the first ([1]) repetition of the third (-3) field in the first PID (PID) segment. Note that PID and PID[1] are equivalent. We could write PID-3[2].4 as PID[1]-3[2].4 For more examples on using HPath see the section "HL7 - Node Path Syntax" in chapter "Node Paths" of the reference manual that ships with QIE.
