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Vocabulary  Work Group | Maturity Level: 5 | Ballot Status: Trial Use |
4.2.1.0.1 Summary 
| Source | SNOMED CT is used in FHIR international standards and resources. SNOMED CT is owned, maintained and distributed by SNOMED International |
| System | |
| Version | Where a code system version is used, it should be specified as a URI that represents a specific SNOMED CT Edition published on a particular date (e.g. the International Edition or a National Edition, with a version date), following the SNOMED CT URI Specification |
| Code | The following SNOMED CT artifacts are valid in the code element for the http://snomed.info/sct namespace: Concept |
and Expressions (grammar Identifiers are not valid as codes in FHIR, nor are other alternative identifiers associated with SNOMED CT Concepts. Note: when SNOMED CT terms must be exchanged, use the Description Id Extension. | |
| Display | The correct display for a SNOMED CT concept is one of the |
terms associated with that concept. The best display is the preferred term in the relevant language or dialect, as specified in the associated language reference set |
. SNOMED CT synonyms may be case sensitive. |
SNOMED International does not define terms for expressions. If a SNOMED terminology producer publishes human-readable terms for expressions in an expression repository, this term may be used as the display. Similarly, if a SNOMED terminology producer publishes an official template for generating terms from an expression, a term generated using the template may be used as the display. If no term or description template has been published, the full expression with terms embedded may be used. Note that Display is not intended to contain terms entered by the user that have not been officially published by a SNOMED CT Terminology Producer. | |
| Inactive | Inactive codes are identified using the 'inactive' property (see below). |
| Subsumption | SNOMED CT Subsumption testing for concepts is based on the |is a| relationship defined by SNOMED CT. |
| Filter Properties | Several filter properties are defined, as described below. |
This specification publishes a canonical SNOMED CT code system resource. See also the SNOMED CT Usage Summary.
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where [sctid] is the concept id that identifies the given SNOMED CT edition (based on the identifier of the most dependent module), and "YYYYMMDD" is the date of release. Examples of sctids that identify a specific edition are are listed here.
4.2.1.0.3
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SNOMED CT Expressions
A SNOMED CT Expression is a structured combination of one or more clinical concepts, stated using Compositional Grammar Syntax.
Expressions may optionally contain display terms.
TODO Advice on the following (requested from LP in comments): What is the guidance when we need to refer to the language refset? what is the guidance when and if we want to define a display term for an expression? What if another term than the preferred term is selected for the display term?
Any number of terms in additional languages and dialects can be specified for a given code in the "Designation" field (eg ValueSet.compose.include.concept.designation ) where the particular language refset to be referred to can be mapped from the language code field "Language"(eg ValueSet.compose.include.concept.designation.language) and the type of the term (ie FSN, Synonym, Definition) is held in the "Use" field ValueSet.compose.include.concept.designation.use.
4.2.1.0.4 Copyright and Licenses Note that many implementations are in the habit of simply using the date of release in the form YYYYMMDD (e.g. "20140531"), and assuming that the edition is known. However this is not always safe, so implementations that populate the version element must use the URI form.
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In addition to the standard properties, the following properties are defined for SNOMED CT:
| Property Name | Data Type | Comments |
| inactive | boolean | Whether the code is active or not (defaults to false). This is derived from the active column in the Concept file of the RF2 Distribution (by inverting the value) |
| sufficientlyDefined | boolean | True if the description logic definition of the concept includes sufficient conditions. This is derived from the definitionStatusId value in the Concept file of the RF2 distribution (i.e. If 900000000000073002 |Sufficiently defined concept definition status| then true). |
| moduleId | code | The SNOMED CT concept id of the module that the concept belongs to |
| . | ||
| normalForm | string | Generated Necessary Normal form expression for the provided code or expression, with terms. See http://snomed.org/nnf |
| normalFormTerse | string | Generated Necessary Normal form expression for the provided code or expression, conceptIds only. |
In addition, any SNOMED CT relationships, where the relationship type is subsumed by 410662002 |Concept model attribute|, also automatically become properties. For example, the laterality property is represented using the conceptId for 410662002 |Laterality|:. Properties that represent SNOMED CT concept model attributes are referred to using their concept id, rather than their human readable term.
For example, the laterality property is represented using the concept id '272741003', rather than the term 'laterality':
| Property Name | Data Type | Comments |
| 272741003 | code | The value of the laterality attribute in the definition of the given code or expression. |
The equivalent URI for the Laterality property is |
Note that when a $lookup operation is performed on a SNOMED CT concept, servers SHALL return the full URI for the edition and version being used (see above) in the version property. Other properties are at the discretion of the server and the client.
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<ValueSet xmlns="http://hl7.org/fhir">
<text>
<status value="generated"/>
<div xmlns="http://www.w3.org/1999/xhtml">
[Some HTML that describes this value set as all concepts in the reference set identified by conceptid]
</div>
</text>
<url value="[edition/version]?fhir_vs=refset/[sctid]"/>
<version value="[edition/version]"/>
<name value="SNOMED CT Reference Set [conceptid]"/>
<description value="All SNOMED CT concepts in the reference set [concept id or preferred description]"/>
<copyright value="This value set includes content from SNOMED CT, which is copyright © 2002+ International Health Terminology Standards Development Organisation (IHTSDO), and distributed by agreement between IHTSDO and HL7. Implementer use of SNOMED CT is not covered by this agreement"/>
<status value="active"/>
<compose>
<include>
<system value="http://snomed.info/sct"/>
<filter>
<property value="concept"/>
<op value="in"/>
<value value="[conceptid]"/>
</filter>
</include>
</compose>
</ValueSet>4.2.1.0.
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10 Implicit Concept Maps
Implicit concept maps are those whose specification can be predicted based on the grammar and/or content of the underlying code system, and the known structure of the URL that identifies them. This allows a single URL to serve as a concept map definition that defines a mapping between two sets of concepts, and which can serve as the basis for the $translate operation. SNOMED CT has two common sets of implicit concept maps defined:
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We've added a new section for Expressions. Bringing other text on the page into line with SNOMED International's definition of what constitutes valid SNOMED CT compositional grammer, we've removed advice about including or not including text definitions - both are considered equally valid, although there may be an argument for including the orginal text selected by the end user.
SNOMED CT Properties
The following property has been removed since "NormalForm" covers this case in that SNOMED CT Expressions are considered valid with our without terms. These can be added or stripped out as required, locally and programmatically, for display purposes.
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New Sections - works in progress
These have been removed into their own pages while the text is agreed. Since they are additional guidance, there is no reason to think that anything being added will 'break' the above.
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