Validating CDA Documents using the PCC Technical Framework

Appendix B - Validating CDA Documents using the Framework

Many of the constraints specified by the content modules defined in the PCC Technical Framework can be validated automatically by software. Automated validation is a very desirable capability, as it makes it easier for implementers to test the correctness of their implementations. With regard to validation of the content module, the PCC Technical Framework narrative is the authoritative specification, not any automated software tool. Having said that, it is still very easy to create a validation framework for the IHE PCC Technical Framework using a XML validation tool such as Schematron. Since each content module has a name (the template identifier), any XML instance that reports itself to be of that "class" can be validated by creating assertions that must be true for each constraint indicated for the content module. In the XML representation, the <templateId> element is a child of the element that is claiming conformance to the template named. Thus the general pattern of a Schematron that validates a specific template is shown below:

<schema xmlns="http://www.ascc.net/xml/schematron" xmlns:cda="urn:hl7-org:v3">
  <ns prefix="cda" uri="urn:hl7-org:v3" />
  <pattern name='ReferralSummary'>
    <rule context='*[cda:templateId/@root="1.3.6.1.4.1.19376.1.5.3.1.1.3]"'>
      <!-- one or more assertions made by the content module -->
    </rule>
  </pattern>
</schema>

Validating Documents

For document content modules, the pattern can be extended to support common document content module constraints as shown below:

<schema xmlns="http://www.ascc.net/xml/schematron" xmlns:cda="urn:hl7-org:v3">
  <ns prefix="cda" uri="urn:hl7-org:v3" />
  <pattern name='ReferralSummary'>
    <rule context='*[templateId/@root="1.3.6.1.4.1.19376.1.5.3.1.1.3]"'>
      <!-- Verify that the template id is used on the appropriate type of object -->
      <assert test='../ClinicalDocument'>
        Error: The referral content module can only be used on Clinical Documents.
      </assert>
      <!-- Verify that the parent templateId is also present. -->
      <assert test='templateId[@root="1.3.6.1.4.1.19376.1.5.3.1.1.2"]'>
        Error: The parent template identifier for medical summary is not present.
      </assert>
      <!-- Verify the document type code -->
      <assert test='code[@code = "34133-9"]'>
        Error: The document type code of a referral summary must be
        34133-9 SUMMARIZATION OF EPISODE NOTE.
      </assert>
      <assert test='code[@codeSystem = "2.16.840.1.113883.6.1"]'>
        Error: The document type code must come from the LOINC code 
        system (2.16.840.1.113883.6.1).
      </assert>
      <!-- Verify that all required data elements are present -->
      <assert test='.//templateId[@root = "1.3.6.1.4.1.19376.1.5.3.1.3.1"]'>
        Error: A referral summary must contain a reason for referral.
      </assert>
      <!-- Alert on any missing required if known elements -->
      <assert test='.//templateId[@root = "1.3.6.1.4.1.19376.1.5.3.1.3.8"]'>
        Warning: A referral summary should contain a list of history of past illnesses.
      </assert>
      <!-- Note any missing optional elements -->
      <assert test='.//templateId[@root = "1.3.6.1.4.1.19376.1.5.3.1.3.18"]'>
        Note: This referral summary does not contain the pertinent review of systems.
      </assert>
    </rule>
  </pattern>
</schema>

Validating Sections

The same pattern can be also applied to sections with just a few minor alterations.

<schema xmlns="http://www.ascc.net/xml/schematron" xmlns:cda="urn:hl7-org:v3">
  <ns prefix="cda" uri="urn:hl7-org:v3" />
  <pattern name='ReasonForReferralUncoded'>
    <rule context='*[templateId/@root="1.3.6.1.4.1.19376.1.5.3.1.3.1"]'>
      <!-- Verify that the template id is used on the appropriate type of object -->
      <assert test='section'>
        Error: The coded reason for referral module can only be used on a section.
      </assert>
      <assert test='false'>
        Manual: Manually verify that this section contains narrative providing the
        reason for referral.
      </assert>
      <!-- Verify that the parent templateId is also present. -->
      <assert test='templateId[@root="1.3.6.1.4.1.19376.1.5.3.1.3.1"]'>
        Error: The parent template identifier for the reason for referral 
        module is not present.
      </assert>
      <!-- Verify the section type code -->
      <assert test='code[@code = "42349-1"]'>
        Error: The section type code of the reason for referral section must be 42349-1
        REASON FOR REFERRAL.
      </assert>
      <assert test='code[@codeSystem = "2.16.840.1.113883.6.1"]'>
        Error: The section type code must come from the LOINC code 
        system (2.16.840.1.113883.6.1).
      </assert>
  </pattern>
  <pattern name='ReasonForReferralCoded'>
    <rule context='*[templateId/@root="1.3.6.1.4.1.19376.1.5.3.1.3.2"]'>
      <!-- The parent template will have already verified the type of object -->
      <!-- Verify that the parent templateId is also present. -->
      <assert test='templateId[@root="1.3.6.1.4.1.19376.1.5.3.1.3.1"]'>
        Error: The parent template identifier for the reason for referral 
        module is not present.
      </assert>
      <!-- Don't bother with the section type code, as the parent template caught it -->
      <!-- Verify that all required data elements are present -->
      <assert test='.//templateId[@root = "1.3.6.1.4.1.19376.1.5.3.1.4.13"]'>
        Error: A coded reason for referral section must contain an simple observation.
      </assert>
      <!-- Alert on any missing required if known elements -->
      <!-- Note any missing optional elements -->
    </rule>
  </pattern>
</schema>

A similar pattern can also be followed for Entry and Header content modules, and these are left as an exercise for the reader.

Phases of Validation and Types of Errors

Note that each message in the Schematrons shown above start with a simple text string that indicates whether the message indicates one of the following conditions:

• An error, e.g., the failure to transmit a required element,
• A warning, e.g., the failure to transmit a required if known element,
• A note, e.g., the failure to transmit an optional element.
• A manual test, e.g., a reminder to manually verify some piece of content.

Schematron supports the capability to group sets of rules into phases by the pattern name, and to specify which phases of validation should be run during processing. To take advantage of this capability, one simply breaks each <pattern> element above up into separate patterns depending upon whether the assertion indicates an error, warning, note or manual test, and then associate each pattern with a different phase. This is shown in the figure below.

<schema xmlns="http://www.ascc.net/xml/schematron" xmlns:cda="urn:hl7-org:v3">
  <ns prefix="cda" uri="urn:hl7-org:v3" />
  <phase id="errors">
    <active pattern="ReasonForReferralUncoded_Errors"/>
    <active pattern="ReasonForReferralCoded_Errors"/>
  </phase>
  <phase id="manual">
    <active pattern="ReasonForReferralUncoded_Manual"/>
  </phase>
  <pattern name='ReasonForReferralUncoded_Errors'>
    <rule context='*[templateId/@root="1.3.6.1.4.1.19376.1.5.3.1.3.1"]'>
      <assert test='section'>
        Error: The coded reason for referral module can only be used on a section.
      </assert>
      <assert test='code[@code = "42349-1"]'>
        Error: The section type code of the reason for referral section must be 42349-1
        REASON FOR REFERRAL.
      </assert>
      <assert test='code[@codeSystem = "2.16.840.1.113883.6.1"]'>
        Error: The section type code must come from the LOINC code 
        system (2.16.840.1.113883.6.1).
      </assert>
    </rule>
  </pattern>
  <pattern name='ReasonForReferralUncoded_Manual'>
    <rule context='*[templateId/@root="1.3.6.1.4.1.19376.1.5.3.1.3.1"]'>
      <assert test='false'>
        Manual: Manually verify that this section contains narrative providing the
        reason for referral.
      </assert>
  </pattern>
  <pattern name='ReasonForReferralCoded_Errors'>
    <rule context='*[templateId/@root="1.3.6.1.4.1.19376.1.5.3.1.3.2"]'>
      <assert test='templateId[@root="1.3.6.1.4.1.19376.1.5.3.1.3.1"]'>
        Error: The parent template identifier for the reason for referral not present.
      </assert>
      <assert test='.//templateId[@root = "1.3.6.1.4.1.19376.1.5.3.1.4.13"]'>
        Error: A coded reason for referral section must contain an simple observation.
      </assert>
    </rule>
  </pattern>
</schema>

Using these simple "templates" for template validation one can simply create a collection of Schematron patterns that can be used to validate the content modules in the PCC Technical Framework. Such Schematrons are expected to be made available as part of the MESA test tools that are provided to IHE Connectathon participants, and which will also be made available to the general public after connectathon.