CDA to CDA transformation

In InterSystems CDA XSLT work, the documents returned here explain these items mainly through examples of custom and preprocessing transforms.

• match is used on xsl:template to define which node a template applies to. Examples shown include matching the root CDA document, any node, text nodes, or a very specific effectiveTime path, such as:

  • match="/hl7:ClinicalDocument"
  • match="node()"
  • match="text()"
  • match="*" in custom extension templates. [1][2][3]

• select is used to choose nodes or values for processing. The examples show it being used with:

  • xsl:apply-templates select="@*" to process attributes
  • xsl:apply-templates select="node()" to process child nodes
  • xsl:copy-of select="@*" to copy attributes
  • xsl:value-of select="hl7:low/@value" to extract an attribute value
  • xsl:variable name="input" select="/hl7:ClinicalDocument" or select="exsl:node-set($inputRTF)/hl7:ClinicalDocument" to define variables from node selections. [1][4][2]

• variable is used to store intermediate results. The preprocessing example shows replacing a direct input variable with:

  • xsl:variable name="inputRTF" to hold the result of applying templates in a custom mode
  • xsl:variable name="input" to convert that result into a node set using exsl:node-set(...).
    
    The debugging section also shows capturing the value of a variable with <xsl:value-of select="$variable"/>. [1][4][2]

• attribute is used to work with XML attributes. The examples show:

  • selecting attributes with @*
  • copying attributes with xsl:copy-of select="@*"
  • reading an attribute such as hl7:low/@value
  • creating an attribute using:
    

    <xsl:attribute name="value">
      <xsl:value-of select="hl7:low/@value"/>
    </xsl:attribute>
    

  • debugging a CDA attribute value with select="/hl7:ClinicalDocument/hl7:id/@root". [1][2]

• copy is used to reproduce nodes. The preprocessing template shows:

  • xsl:copy to copy the current node
  • xsl:copy-of select="@*" to copy all attributes
  • then xsl:apply-templates select="node()" to continue recursively through children.
    
    The debugging section also states that calling the copy template with mode="copy" returns the current XPath tree. [1][2]

• mode is important in InterSystems CDA customization. The preprocessing examples use a custom mode such as mo:MyMODEname so that special preprocessing templates are called separately from the main transform. The top-level transform is then modified to call:

  <xsl:apply-templates select="/hl7:ClinicalDocument" mode="mo:MyMODEname"/>
  

  This lets you run a preprocessing pass before the standard transform uses the resulting document. The customization guide also shows other modes such as ImportCustom-Container, ImportCustom-Procedure, currentXPathWithPos, currentXPath, and copy. [1][4][2]

• For custom CDA transformations in general, the documented pattern is:

  1. create a Custom subdirectory,
  2. create a custom XSL with the same name,
  3. import the original XSL with <xsl:import href="../<filename>"/>,
  4. copy the template you want to override,
  5. change its logic,
  6. restart productions to activate it. [2]

• For CDA structure, the returned material also notes that the root node is <ClinicalDocument>, with header, sections, and entries beneath it, and transformations for sections and entries are driven by support files. That helps explain why template match expressions often target specific CDA paths. [3]

Important: If you plan to customize transformations and InterSystems IRIS for Health is running in a Docker container, the container must point to a durable directory. For more information on durable directories, see Running InterSystems Products in Containers. [2]

If you want, I can next turn this into a small CDA XSLT example showing each of match, select, variable, attribute, copy, and mode in one sample transform.

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