SNOMED CT® Release Format 1 (RF1) Guide - ihtsdo

24 | SNOMED CT Release Format 1 (RF1) Guide July 2012
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These extra components should behave as though they were components of SNOMED CT but they
should be distinguishable from components that are part of the SNOMED CT International Release.
• Globally unique identification of any terminology component that may be used outside the scope of a
limited local environment:
• The mechanism must allow several organizations to issue mutually exclusive Identifiers for components
of their Extensions.
• To avoid the risk of misinterpretation, this mechanism must be effective in various contexts including:
• Within the thesaurus;
• In patient records;
• In queries, decision-support protocols or knowledge bases.
• The mechanism must indicate when Concepts have moved, or are expected to move, between an
Extension and the International Release, or from one Extension to another.
• A shared understanding of the responsibility of an organization that creates an Extension and provides
it for the use of other organizations . These responsibilities include:
• Maintenance of the Concept, Descriptions, Relationships, and Subsets;
• Inactivation of these components as appropriate (duplication, ambiguous, outdated, etc.);
• Submission to an IHTSDO Member's National Release Centre for consideration as an addition to
a National Edition or to the International Release content.
2.1.4. Instance data
2.1.4.1. Introduction
This section describes the use of SNOMED CT to express clinical ideas in patient records, messages,
documents, decision support protocols, queries and other artifacts .
Applications need to create, manipulate and consistently interpret standard SNOMED CT representations in
instance data to support the entry, storage, retrieval and communication of clinical information.
2.1.4.2. Expressions
An expression is a structured combination of one or more concept Identifiers used to express an instance of
a clinical idea.
• Pre-coordinated expression: An expression containing a single concept Identifier is pre-coordinated.
The clinical idea it expresses is represented by the identified concept. The defining relationships of that
concept pre-coordinate its meaning.
• Post-coordinated expression: expression that contains two or more concept Identifiers is post-coordinated.
The concept Identifiers in a post-coordinated expression are related to one another in ways that build a
more specific clinical idea. The required meaning is expressed by post-coordinating several clinical ideas
each of which is represented by an identified concept.
Example: A post-coordinated expression can indicate the specific site of a finding even when that
specific combination of disorder and site is not represented by a single SNOMED CT Concept.
2.1.4.3. Terminology Bindings
Terminology binding is one part of the process of specifying constraints on the way that information is structured
and represented.
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