SNOMED CT canonical CodeSystem resource

The FHIR specification has an incomplete canonical CodeSystem resource at http://build.fhir.org/codesystem-snomedct.html(or the earlier / published version: https://www.hl7.org/fhir/codesystem-snomedct.html )

This is something SNOMED International should really take ownership of, complete it, host it and keep it up to date...but obviously this group can help with all of that (except the hosting!).

I've included a table below which indicates the elements and their values in the current resource. The other thing to consider is the HTML rendering and what it should say, the current one you can see at https://www.hl7.org/fhir/codesystem-snomedct.html is in the current resource as generated text from the resource.

Ideally this should be hosted at http://snomed.info/sct and behave as a proper FHIR endpoint (e.g. respond appropriately to JSON and XML accept headers).

Please comment on the appropriateness of the current values and suggested changes.

Element	Value	Discussion

Element

Value

Discussion

id

snomedct

Specified by individual server, so we could leave blank here.

url

http://snomed.info/sct

We'd expect this to redirect to the most recent international release.

version

This probably should be a specific URI to the particular edition/version but not defined in the Canonical form.

Suggest we mandate this field if this document is specifying a template. RH had concerns about this since concepts couldn't then be referred between different versions. Note that the context here is an instance of a Code System resource from at Term Server perspective, not individual concepts as used a medical record where the SCTID plus description provides meaning.

identifier

system	urn:ietf:rfc:3986
value	urn:oid:2.16.840.1.113883.6.96

This is the SNOMED OID used in other specifications eg CDA.

name

SNOMED CT

While this is the canonical value, each server would specify the particular edition they're making available.

title

SNOMED CT (all versions)

Not required?

status

active

experimental

false

publisher

IHTSDO

Change to SNOMED International

contact

telecom

system	url
value	http://ihtsdo.org

Changes to snomed.org

description

SNOMED CT is the most comprehensive and precise clinical health terminology product in the world, owned and distributed around the world by The International Health Terminology Standards Development Organisation (IHTSDO).

@Peter Williams check current text

copyright

© 2002-2018 International Health Terminology Standards Development Organisation (IHTSDO). All rights reserved. SNOMED CT®, was originally created by The College of American Pathologists. "SNOMED" and "SNOMED CT" are registered trademarks of the IHTSDO http://www.ihtsdo.org/snomed-ct/get-snomed-ct

@Peter Williams check current text. Next release will take year up to 2019.
That URL is now https://www.snomed.org/snomed-ct/get-snomed

caseSensitive

false

Definition of element here is "If code comparison is case sensitive" which because SCTIDs are numeric, it's not.

hierarchyMeaning

is-a

Suggest improving the documentation for this element, is somewhat ambiguous. "Properties of parent apply to child" is certainly true.

compositional

true

"True If code system defines a post-composition grammar."

versionNeeded

false

"This flag is used to signify that the code system has not (or does not) maintain the definitions, and a version must be specified when referencing this code system."

content

not-present

We're not expecting to include all of SNOMED-CT in this resource.

filter

code

description

operator

value

concept

Filter that includes concepts based on their logical definition. e.g. [concept] [is-a] [x] - include all concepts with an is-a relationship to concept x, or [concept] [in] [x]- include all concepts in the reference set identified by concept x

is-a

in

A SNOMED CT code

expression

The result of the filter is the result of executing the given SNOMED CT Expression Constraint

=

A SNOMED CT ECL expression (see ecl)

expressions

Whether post-coordinated expressions are included in the value set

=

true or false

RH notes that the distinction between plural and not is subtle in text and substantial in effect.

Could use "constraint" for the first instance. However, is likely already in use. ML confirms and in fact this field was previously called "constraint".

"PostCoordination" a suggested alternative for 2nd which is the more problematic of the two.

ML: Is "expressions" more relevant to an expansion profile? PW: Changing "are" to "should be" would make intention clearer.

@Dion McMurtrie contact GG to track down where "expressions" came from and confirm the use case is? Has been there for some time. Posted on chat.fhir.org at https://chat.fhir.org/#narrow/stream/89-snomed/topic/SNOMED.20CT.20filters

property

code	uri	description	type
inactive	http://snomed.info/field/Concept.active	Whether the code is active or not (defaults to false). Not the same as deprecated	boolean
definitionStatusId	http://snomed.info/field/Concept.definitionStatusId	Either of the codes that are descendants of 900000000000444006	code
parent	http://hl7.org/fhir/concept-properties#parent	A SNOMED CT concept id that has the target of a direct is-a relationship from the concept	code
child	http://hl7.org/fhir/concept-properties#child	A SNOMED CT concept id that has a direct is-a relationship to the concept	code
moduleId	http://snomed.info/field/Concept.moduleId	The SNOMED CT concept id of the module that the concept belongs to.	code
normalForm	http://snomed.org/longnormalform	Generated Normal form expression for the provided code or expression, with terms	string
normalFormTerse	http://snomed.org/canonicalnormalform	Generated Normal form expression for the provided code or expression, conceptIds only	string

We need URI values for parent / child and Normal Form here.

If / when the URI standard is extended to include ECL then parent / child would arrive that.

ML: parent and child are general properties that are not SNOMED specific, these are FHIR specified properties. Have inserted FHIR URIs here.

Suggestion that normalFormTerse is changed to Canonical Normal Form, and normalForm changed to Necessary Long Normal Form (and use these terms in the description column also, with sufficient text to explain the difference between the two).

URI is, also, optional.

Noted the impact on implementers in changes here, so name changes noted above will not be recommended at this time.

@michael lawley to take up the URIs for Normal Forms with the SNOMED Languages Group.

However in any event, the description should be updated here.

@Dion McMurtrie to update description text.

property (cont)

There is also listed the attributes used in SNOMED CT, a couple of examples to express the pattern are

code	uri	type
Due to	http://snomed.info/id/42752001	code
Associated with	http://snomed.info/id/47429007	code

Code should be the SCTID rather than term.

@Rob Hausam How is this list defined? Descendants of "Attribute" ?

Perhaps more relevant to use attributes currently in use in the International Edition.

FSN should be populated in the description column.

Additional elements worth considering populating are

date - date of last change to the resource
purpose - why is this code system defined
valueSet - Canonical URL for the value set with the entire code system

DM suggested date was worth populating to show when the resource last changed.

Boiler plate text for purpose?

"SNOMED CT (Systematized Nomenclature of Medicine -- Clinical Terms) is a standardized, multilingual vocabulary of clinical terminology that is used by physicians and other health care providers for the electronic exchange of clinical health information."

https://searchhealthit.techtarget.com/definition/SNOMED-CT

The URL for the entire code system is a notional valueset that contains all versions of all editions. It would not change from instance to instance and is immutable.

Another thing to consider is whether the valueSet, if it can exist, if theoretically expanded would return all of SNOMED CT International Edition or the SNOMED CT "Universal" Edition - i.e. which does this CodeSystem resource represent?

To be defined for the individual code systems. Could state the implicit value set endpoint for the server.