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Structure of traditional coding and classification schemes

All the major medical coding and classification schemes, such as the International Classification of Diseases and the Read Clinical Classification, are based on the enumerative classification of concepts and terms . These schemes are constructed entirely by experts enumerating all the possible concepts that are to be represented within the scheme. A concept is represented by an atomic code with an associated rubric that corresponds to the term. The classificatory relationships between the concepts are usually represented in the structure of the codes — for example the code A1234 might be classified under the code A1230. More recent developments have separated the parent-child relationship from the actual code-symbol into a separate piece of information, but the relationships are still created manually.

These relationships are constructed entirely by human judgement and effort, based on reading the rubrics and applying expert medical knowledge. Thus the classification of the terms is also achieved by the enumeration of relationships. The result is a static structure that embodies a particular set of choices and goals. Furthermore the medical reasoning and knowledge that went into building the scheme is locked up inside the rubrics, and can not be used by any automatic system. A clinician may be able to make sense of the words ‘acute myocardial infarction’ but a computer can not.

Such an approach was appropriate when the context was limited to summary descriptions, a single purpose, and interpretation by skilled humans, in a single language. It was feasible for experts to define a list of required terms, and classify these in a way that aligned well with the intended purpose for the scheme. However the demand for large numbers of complex concepts, arranged in multiple ways, and capable of automatic interpretation and possible transmission in alternative languages has revealed fundamental problems with enumerative classifications.

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