5.3 Encoding
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## 5.3 Encoding

A full discussion of the representation of data types and vocabulary is outside the scope of this document; for more information, see the HL7 V3 specifications on Abstract Data Types R1 and XML Data Types R1 referenced in the CDA Specification.

### Note

1. Many Data Types encode their values in attributes, rather than character data. For example, the URL Data Type encodes its value in the value attribute within the element tag, e.g., <reference value="http://xyz.org">. Within this specification, the attribute(s) that hold the value are not identified, except where specific constraints apply.

2. The Consolidated CDA specification includes extensive examples of valid and invalid encodings, which may be useful for implementers.

3. The specification of a representation of Data Types for use in Business Name-based report production logic is outside the scope of this Standard.

### 5.3.1 Translation Code Element

HL7 Data Types CD (Concept Descriptor) and CE (Coded With Equivalents) allow a translation code element, which allows the encoding of the same concept in an alternate coding system. This supports the encoding of both an originally entered (local) code, and a code specified for cross-system interoperability.

This Part follows the convention used in the Consolidated CDA Implementation Guide specification, which specifies the standard interoperable code in the root, whether it is original or a translation. The HL7v3 Data Types R1 standard included by CDA formally specifies the original code (as initially entered in an information system application) to be placed in the root.

### Note

This discrepancy is resolved in HL7v3 Data Types R2 to follow the convention used here, and the HL7 Structured Documents Working Group has approved the "pre-adoption" of the Data Types R2 approach in CDA implementations.

Example 5.3.1-1. Translation code example

    <code code='206525008'
          displayName='neonatal necrotizing enterocolitis 'codeSystem='2.16.840.1.113883.6.96'
          codeSystemName='SNOMED CT'>
        <translation code='NEC-1'
          displayName='necrotizing enterocolitis'
          codeSystem='2.16.840.1.113883.19'/>
    </code>

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