Dependencies

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IP Statements

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<a name="hl7v2"></a>

Use of FHIRPath on HL7 Version 2 messages

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FHIRPath can be used against HL7 V2 messages. This UML diagram summarizes the Object Model on which the FHIRPath statements are written:

{: height="456",width="760"}

In this Object Model:

• The object graph always starts with a message.
• Each message has a list of segments.
• In addition, Abstract Message Syntax is available through the groups() function, for use where the message follows the Abstract Message Syntax sufficiently for the parser to reconcile the segment list with the structure.
• The names of the groups are the names published in the specification, e.g. 'PATIENT_OBSERVATION' (with spaces, where present, replaced by underscores. In case of doubt, consult the V2 XML schemas).
• Each Segment has a list of fields, which each have a list of "Cells". This is necessary to allow for repeats, but users are accustomed to just jumping to Element - use the function elements() which returns all repeats with the given index.
• A "cell" can be either an Element, a Component or a Sub-Components. Elements can contain Components, which can contain Sub-Components. Sub-Sub-Components are not allowed.
• Calls may have a simple text content, or a series of (sub-)components. The simple() function returns either the text, if it exists, or the return value of simple() from the first component
• A V2 data type (e.g. ST, SN, CE etc) is a profile on Cell that specifies whether it has simple content, or complex content.
• todo: this object model doesn't make provision for non-syntax escapes in the simple content (e.g. \.b\).
• all the lists are 1 based. That means the first item in the list is numbered 1, not 0.

Some example queries:

Message.segment.where(code = 'PID').field[3].element.first().simple()

Get the value of the first component in the first repeat of PID-3

Message.segment[2].elements(3).simple()

Get a collection with is the string values of all the repeats in the 3rd element of the 2nd segment. Typically, this assumes that there are no repeats, and so this is a simple value.

Message.segment.where(code = 'PID').field[3].element.where(component[4].value = 'MR').simple()

Pick out the MR number from PID-3 (assuming, in this case, that there's only one PID segment in the message. No good for an A17). Note that this returns the whole Cell - e.g. |value^^MR|, though often more components will be present)

Message.segment.where(code = 'PID').elements(3).where(component[4].value = 'MR').component[1].text

Same as the last, but pick out just the MR value

Message.group('PATIENT').group('PATIENT_OBSERVATION').item.ofType(Segment)
  .where(code = 'OBX' and elements(2).exists(components(2) = 'LN')))

Return any OBXs from the patient observations (and ignore others e.g. in a R01 message) segments that have LOINC codes. Note that if the parser cannot properly parse the Abstract Message Syntax, group() must fail with an error message.

FHIRPath Tooling and Implementation

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The list of known tooling and implementation projects for the FHIRPath language has been moved to the HL7 confluence site{:target="_blank"}

Cross Version Analysis

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Global Profiles

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