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2015-09-01 10:47

Identification of objects required by interoperability

Interoperability of healthcare data and systems requires specific methods of identification of objects represented in those systems.

The basic rule of interoperability is elimination or reducing the need of agreeing formats and protocols between parties attempting exchange of information. If particular object (e.g. patient, physician, document, event) is to be recognized by recipient of the document or message in the same way as by its author or sender, then identifiers being used have to be globally unique and verifiable outside the context of exchange.

Fortunately, it does not mean that legacy local identifiers have to be necessarily replaced by new global ones, but it requires unequivocal indication of the identification systems used. HL7 standards implement a method based on global system of object identification ISO OID. Identifier conformant to the standard consists of two parts: legacy local object identifier and unique OID node representing the identification system being used. Thereby, the composition of the legacy identifier and the identification system indicator becomes the new globally unique identifier. The proper use of such complex identifier requires that the legacy identifier namespace has been submitted to the official ISO OID registry and the OID node has been assigned and published.

For that reason, each implementation of HL7 standard requires publication of an OID registry, containing at least those OID nodes, that have been assigned while the implementation was developed. In Poland the ISO OID system was not popular so far. It was required in verification paths of qualified certificates, but in healthcare systems was not commonly used. The official rules of development for clinical documents in electronic form, being the polish national implementation guide of HL7 CDA standard developed by the National Centre for Healthcare Information Systems (CSIOZ), require usage of ISO OID based identification system. Thus, the CSIOZ has developed, published and maintains its own OID registry, containing all OID nodes required by the rules, specific for Polish healthcare system.

It is worth noting, that in practice it adopted up, as an exception from the general rule of building complex identifiers, usage of single-part identifier being just an OID node, for some object types like organizations and code systems. For organizations it allows to create and develop their own OID tree in the node identifying the organization. For code systems, like terminology dictionaries, the second part of the identifier is the actual code of the dictionary entry.


Roman Radomski, iEHR.eu

Expert in implementation of interoperability standards, certified by HL7 International, co-author of the Polish National Implementation Guide for HL7 CDA.