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In some situations, however, the specific concepts or values are not known at the time of authoring. In these cases, one or more slots may be used within an expression or expression constraint to create an expression template or expression constraint template (respectively). Slots provide a placeholder in the expression or expression constraint, whose specific value can be completed at a subsequent time using a concept recorded within an information model, entered into a data entry form, or sourced by some other means. When each slot in the template has been replaced with a specific value, the result should be a syntactically correct expression or expression constraint. SNOMED CT templates can be used for a number of purposes, including to define reusable patterns for authoring and validating precoordinated concept definitions and postcoordinated expressions.
History
The SNOMED CT Template Syntax (v1.0) was first published in July 2017. In 2020, the syntax was updated (v1.1) to support boolean attribute values.
Purpose
The purpose of this document is to define and describe a consistent mechanism for SNOMED CT templates, which can be used to convert any computable SNOMED CT language into a SNOMED CT template language. For example, by using the syntax provided in this document, SNOMED CT compositional grammar can be used as an expression template language, and the SNOMED CT expression constraint Language can be used as an expression constraint template language. This guide also provides examples and guidance to assist in the processing of templates.
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- Compositional Grammar: designed to represent SNOMED CT expressions;
- Expression Constraint Language: designed to represent a bounded set of clinical meanings represented using SNOMED CT; and
- Query Language: designed to express computable queries over SNOMED CT content.
This document provides a specification, examples and general guidance to assist in the representation and processing of SNOMED CT templates.
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This document defines the SNOMED CT template syntax and describes how and where it may be implemented. Chapter 2 begins by describing some key use cases in which SNOMED CT templates can be used. Chapter 3 then describes the requirements used to guide the definition of this syntax. In Chapter 4, the logical model of the template syntax is presented, while Chapter 5 defines the ABNF serialisation of the logical model. Chapter 6 explains how to apply the SNOMED CT template syntax to other computable languages, and provides the syntax for the expression template language (ETL). In chapter 7, we explain the steps involved in processing an expression template to create a set of populated expressions. And finally, in chapter 8, we present some examples of SNOMED CT expression templates that conform to the syntaxes defined in Chapters 5 and 6.
Glossary
The following table contains the definition of terms used within this document. Please refer to the IHTSDO Glossary for additional SNOMED CT definitions.
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Definition
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Augmented Backus-Naur Form (ABNF)
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A language used to define the formal syntax of another language (as defined by Internet Standard 68, RFC 5234).
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The set of rules that govern the way in which SNOMED CT expressions are represented as a plain text string.
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A set of rules that determines the permitted sets of relationships between particular types of concepts.
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A structured combination of one or more concept identifiers used to express a clinical idea.
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Expression Constraint
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A computable rule that can be used to define a bounded set of clinical meanings.
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Representation of a clinical meaning using a combination of two or more concept identifiers is referred to as a postcoordinated expression.
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Representation of a clinical meaning using a single concept identifier is referred to as a precoordinated expression.
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A SNOMED CT file structure consisting of a set of references to SNOMED CT components.
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Substrate
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The SNOMED CT content over which an expression constraint is evaluated or a query is executed.
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