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An innovative approach to the issues raised by literal storage of is to implement an repository. Each unique used in the system is stored in a referenced database table and assigned an internal unique (e.g. a UUID). When an is used in a clinical record entry the unique id is used to reference the in the repository.


  • The can have a fixed size whereas a in of variable and indeterminate size. This significantly improves storage and index efficiency.
  • The repository can also be used to store representations of each and to relate these to the original . This optimizes performance for normalization during retrieval.
  • The repository could also be processed by a and a table of all the used in the application could then be generated. retrieval would then be highly optimized by using the to test a single join between each predicate and the candidate .

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Both are equally close to the objective of minimizing . A rule is needed to determine which of these is preferred. There is no obvious right or wrong solution to this but a simple rule that places the attributes in an order will, if applied consistently, allow all representations to be reduced to a single minimized form.


If the retrieval criteria are expressed in a similar form, a relatively simple query can interrogate the record for all entries with a matching set of and specified characteristics.