Note that this page has been copied from http://build.fhir.org/snomedct.html purely for the purpose of review and consolidating feedback. It would be acceptable to modify this document however, so we have a 'complete' draft to return to HL7. We'll be able to track the changes through Confluence document history.
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 |
SNOMED International is |
the international organization |
which publishes the international release of SNOMED CT |
. SNOMED International member countries may also distribute their own SNOMED CT edition, which contains the international release plus local extension content and derivatives. | |
| System | |
| Version | Where a version is used, it should be a |
URI that represents the specific distribution (International Release, or National Release and version), 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 IDs , Expressions (grammar ) and SNOMED Legacy codes .SNOMED CT Terms (Description Ids) are not valid as codes in FHIR, nor are other alternate identifiers associated with SNOMED CT Concepts using the RF2 identifier infrastructure. Expressions SHOULD NOT contain terms, only concept IDs (note that 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 synonyms for the concept. The best display is the preferred term in the relevant language reference set (if applicable). Preferred terms are case sensitive. The Fully Specified Name is not an appropriate choice. The source of preferred name comes from a Language Reference Set. SNOMED CT does not define displays for expressions; if no display has been associated with the expression through a value set or other mechanism, the full expression syntax with preferred terms embedded may be used |
| Inactive | Inactive codes are identified using the 'inactive' property (see below) |
| Subsumption | SNOMED CT Subsumption testing is based in the |is a| relationship defined by SNOMED CT |
| Filter Properties | Several properties are defined as described below |
This specification publishes a canonical SNOMED CT code system resource. See also the SNOMED CT Usage Summary.
Note: The IHTSDO glossary SNOMED International glossary explains some of these SNOMED CT specific terms.
...
where [sctid] is the concept id of the SNOMED CT distribution (e.g. 32506021000036107 for Australia), and the tail is the date of release (by custom, this is usually the last day of the month). Note that many implementations are in the habit of simple using the date of release in the form YYYYMMDD (e.g. "20140531"), and assuming that the distribution is known. However this is not always safe, so implementations that populate the version element SHOULD must use the full URI form.
4.2.1.0.3 Copyright/License Issues
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The IHTSDO URI specifications uses the namespace http://snomed.info/sct for the code system, and the URI http://snomed.info/id for the individual concepts in the code system. This means that when a SNOMED CT concept is converted from the system::code pair, where the system is http://snomed.info/sct, to the RDF ontological form, the representation is http://snomed.info/id/[concept-id]. Expressions are represented the same way, except that for this use, expressions SHALL not contain whitespace, terms, or comments.
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In addition to the standard properties, the following properties are defined for SNOMED CT:
| 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 (i.e., if the concept is not primitive - found in the value of definitionStatusId in the concept file). |
| moduleId | code | The SNOMED CT concept id of the module that the concept belongs to. |
| normalForm | string | Generated Normal form expression for the provided code or expression, with terms |
| normalFormTerse | string | Generated Normal form expression for the provided code or expression, conceptIds only |
In addition, any SNOMED CT relationships where the relationship type is subsumed by Attribute (246061005) automatically become properties. For example, laterality:
| Laterality | code | In this case, the URI (See the code system definition) is http://snomed.info/id/272741003, which can be used to unambiguously map to the underlying concept |
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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For implementer convenience, some of the property filters are documented in terms of the SNOMED CT Query Language Expression Constraint Language, but this does not imply that its use is required.
4.2.1.0.6.1 By Subsumption
| Description | Select a set of concepts based on subsumption testing |
| Property Name | concept |
| Operations Allowed | is-a |
| Values Allowed | [concept id] |
| Comments | Includes all concept ids that have a transitive is-a relationship with the concept Id provided as the value (including the concept itself) |
| Example | Administration Methods |
<< [concept] (or the long form: descendantOrSelfOf [concept]) |
4.2.1.0.6.2 By Reference Set
| Description | Select a set of concepts based on their membership of a SNOMED CT reference set |
| Property Name | concept |
| Operations Allowed | in |
| Values Allowed | [concept id] |
| Comments | Includes all concept ids that are active members of the reference set identified by the concept Id provided as the value |
^ [concept] (or the long form: memberOf [concept]) |
4.2.1.0.6.3 By SNOMED Query Expression
| Description | Select a set of concepts based on a formal expression statement |
| Property Name | constraint |
| Operations Allowed | = |
| Values Allowed | [expression] |
| Comments | The result of the filter is the result of executing the given SNOMED CT Expression (Expression Constraint Language) . Example: "compose": {
"include": [
{
"system": "http://snomed.info/sct",
"filter": [
{
"property": "constraint",
"op": "=",
"value": "<< 30506011000036107 |Australian product|: 700000101000036108 |hasTP| = 17311000168105 |Panadol|"
}
]
}
]
}
|
4.2.1.0.6.4 By whether post-coordination is allowed
| Description | Specify whether post-coordination is allowed or not |
| Property Name | expressions |
| Operations Allowed | = |
| Values Allowed | true or false |
| Comments | Expressions, if allowed, are subject to the same rules as pre-coordinated concepts. (Note: simple reference sets do not include expressions, but Query specification reference sets might). |
| Example | Administration Methods |
n/a |
4.2.1.0.7 Implicit Value Sets
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Association Reference Sets are part of the core SNOMED CT distribution. The following standard Association Reference sets are mapped to implicit Concept Maps:
| Name | Concept Id | Relationship |
| POSSIBLY EQUIVALENT TO | 900000000000523009 | inexact |
| REPLACED BY | 900000000000526001 | equivalent |
| SAME AS | 900000000000527005 | equal |
| ALTERNATIVE | 900000000000530003 | inexact |
If any concept map resources exist with an identifier that conforms to the URL pattern specified below, the content of the resource must conform to the template provided. Canonical references to concept maps are allowed to reference these concept maps directly by referring to their URI.
...
Simple Map Reference Sets (reference sets which are descendants of 900000000000496009 "Simple map") also define an implicit concept map. However, at this time, these cannot be converted to Concept Maps because there is no source for the target code system. Another reference set has been proposed to IHTSDOSNOMED International, and this section will be revisited once it is adopted.