ExternalURI

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Contents

Introduction

Section 2.1.3 of CTS2 Core Model Specification differentiates persistent and local URI's. Local URI's resolve to "digital resources" that serve to describe external resources. Persistent URI's reference resources that the CTS2 information is about.

While CTS2 supports the ability to reference the same resource (Class, Property, Individual, Code System, Map, Document, ...) with more than one URI, it is still in everyone's best interest to use as few URI's for any given resource as is possible - ideally, one. To accomplish this goal, the CTS2 community has been actively pursuing the establishment of official URI's - ideally sanctioned by the body that is primarily responsible for publishing the terminologies themselves.

Ideally, an official, sanctioned URI will have the following characteristics:

  1. It will use the http protocol
  2. The host portion of the URI will be owned by the same organization that publishes the terminology, map, value set or other resource
  3. The URI will resolve to a page that will, at a bare minimum, confirm that the URI is, indeed, sanctioned by the publishing body.

The sections below describe the various URI schemes that are in various stages of being implemented:

URI Schemes

IHTSDO / SNOMED CT

The CTS2 Implementation Guide proposes the following additions:

WHO / ICD, etc.

The following documentation is not yet final and is awaiting verification from the WHO.

(to be continued)

HL7

To date, HL7 has used ISO Object Identifiers (OIDS) to reference code systems and value sets. Unfortunately, there is no sanctioned algorithmic way to reference versions of code systems, concepts in code systems or specific definitions (versions) of value sets without assigning a unique numeric identifier to each resource. While the OID approach works in structured data represented in the HL7 V3 or ISO 21090 data types, there is currently no way to represent a specific concept in a specific code system as a single URI. For this reason, we advocate the use of http URI's throughout.

Fortunately, HL7 is encountering the same issue as part of the MIF to OWL conversion project. More to come shortly

UMLS

An ideal URI would be created by the terminology publisher, as described in the previous sections. When this is not available, however, the next option is to use a URI generated by an authoritative resource that is knowledgeable about the terminology publisher and can act as a proxy for the actual publisher. The NLM fits this role perfectly when it comes to the medical terminologies that are published in the UMLS. The NLM has proposed the following identification scheme: