Extensions Practical Guide

Search

SNOMED CT Document Library

    Loading...

Page tree

Versions Compared

Old Version 4

changes.mady.by.user Anne Randorff Højen

Saved on

compared with

New Version 5

changes.mady.by.user Anne Randorff Højen

Saved on

Key

  • This line was added.
  • This line was removed.
  • Formatting was changed.

Purpose 

Concepts may be added to an extension to provide new clinical ideas which are not represented in the International Edition. The primary reason for adding concepts to an extension is to represent meanings which are outside the scope of the International Edition, yet within the scope of SNOMED CT. These might be concepts which have local relevance, within a single country, territory or organization. Concepts may also be added to an extension to represent metadata about the extension, for example module concepts, reference set concepts, or new attributes.

For a more detailed introduction on the purposes for adding concepts to an extension, please refer to Section 3 Purpose.

Principles

Overview

Key principles for authoring concepts in an extension include

  • Concepts added to an extension must have a moduleId that includes the namespace identifier assigned to that extension producer by SNOMED International
  • An extension concept must comply with the logical design of SNOMED CT components and maintain referential integrity
  • Concepts added to an extension should conform to the policies stated in 5.3.2 Constraints on Concept Requests
  • Use caution when authoring an intermediate concept in an extension, i.e. a concept which is a supertype of a concept in the International Edition

Essential Descriptions and Relationships

A concept created in an extension must conform to the logical design of SNOMED CT concepts. An overview of the logical model is provided in . This means that every concept created in an extension must have:

  • At least one
    Concept
    ShowPartsterm
    t116680003 Is a
     relationship
  • At least one description of type
    Concept
    ShowPartsterm
    t900000000000003001 Fully specified name
  • At least one description of type
    Concept
    ShowPartsterm
    t900000000000013009 Synonym

Additional Descriptions and Relationships

Concepts created in an extension may also have additional descriptions and defining relationships.

Additional defining relationships may include

Concept
ShowPartsterm
t116680003 Is a
 relationships and attribute relationships. When specifying attribute relations for an extension concept it is important to ensure compliance with the SNOMED CT concept model. The concept model specifies the attributes that can be applied to particular types of concepts and it specifies the permitted values for each of these attributes. There are also additional rules on the cardinality and grouping of particular types of relationships. Please see the SNOMED CT Editorial Guide and the SNOMED CT Machine Readable Concept Model for details on the concept model rules. 


Retaining Referential Integrity

As discussed in module dependencies, all extensions have modules which depend on the modules in the International Edition. Extensions may also have modules which depend on the modules from other extensions. Despite the dependencies between modules from various editions, all concepts in an extension must be a subtype of the root concept,

Concept
t138875005 | SNOMED CT Concept|
. This ensures that a concept in an extension can be queried and retrieved in a similar way to any concept in the International Edition. Put another way, queries which use subsumption should be able to identify a concept which belongs to a module in an extension because it is a subtype of a concept from the International Edition.

...

The referential integrity of a concept in an extension is retained by the addition of at least one

Concept
ShowPartsterm
t116680003 |is a|
 relationship to a parent concept that is subsumed by
Concept
ShowPartsterm
t138875005 | SNOMED CT Concept|
. The parent may be a concept which is part of a module within the extension, another extension, or the International Edition. 

Leaf and Intermediate Extension Concepts

When an extension producer creates a new concept and states one or more

Concept
ShowPartsterm
t116680003 |is a|
 relationships to define that concept the immediate effect is to make the new concept a leaf concept in the SNOMED CT subtype hierarchy.  That is to say the new concept at this point has no known subtypes.

...

Note
iconfalse
titleNote

If an extension producer makes any changes or additions within their extension, which result in modification of the transitive closure of the International Edition, they must report this to SNOMED International. This will allow the issue that necessitated the change to be assessed and where appropriate resolved in the Internation Edition.

Examples

The following 3 examples illustrate the impact of adding extension concepts as leaf concepts or intermediate concepts (after classification). The impact is considered in terms of how each addition effects subsumption testing  using an example international concept 'G'. 

...

Illustration

Impact on hierarchy

The definition of a concept in an extension module may result in it being classified as an intermediate concept in the SNOMED CT polyhierarchy, as illustrated in the diagram above.

This scenario results in the creation of two new inferred

Concept
ShowPartsterm
t116680003 |is a|
relationships in the extension, i.e. the relationships G | is a | X and X | is a | E. The inferred relationship G | is a | E (green dotted line), which is present in the international edition, becomes redundant when classified together with the extension (therefore marked grey in the diagram).

Impact on subsumption

This type of intermediate extension concept does not change the results of subsumption testing between international concepts. It does, however, have an impact on which relationships from the international edition are non-redundant in the extension edition. In this example, the inferred relationship G |is a| E becomes redundant when combined with the inferred relationships from the extension.

Extension producers can handle this redundancy by:



Illustration

Impact on hierarchy

The definition of a concept in an extension module may result in it being classified as an intermediate concept in the SNOMED CT polyhierarchy , as illustrated in the diagram above .

This scenario results in the creation of three new inferred

Concept
ShowPartsterm
t116680003 |is a|
relationships in the extension, i.e. the relationships G | is a | X and X | is a | D and X | is a | E. The inferred relationship G | is a | E (green dotted line), which is present in the international edition, becomes redundant when combined with the inferred relationships from the extension. Furthermore, the definition of the extension concept X results in a modification of the definition of the international concept G, as G is now a subtype of the international concept D.

Impact on subsumption

This type of intermediate extension concept may change the results of subsumption testing for particular international concepts, when used within the local edition. Extension producers should therefore exercise extreme caution when introducing this type of concept addition.

When using the International Edition on its own, the concept G will not be treated as a subtype of the concept D. However, users of this example extension edition will see the international concept G as a subtype of the international concept D. This means that queries over international concepts stored in clinical data will lead to different results, depending on which edition is used. Therefore, intermediate concepts of this type may have serious consequences on the comparability and interoperability across SNOEMD CT Editions.

Process

Concepts added to an extension are represented in a concept file. These concepts are part of a module which includes the namespace identifier assigned to the extension producer by SNOMED International. Each concept also requires additional components and reference set members to be defined. At a minimum, the following components and derivatives should be created:

...

Pdf font sizer


File TypeProcess
Concept

A new concept identifier is allocated within the extension namespace.

The attributes of the new concept are set as follows:

  • id is set to the new concept identifier allocated within the extension namespace
  • effectiveTime is set to the date the extension will be published
  • active is set to 1 to indicate that the new concept will be active at the time of publication
  • moduleId is set to the conceptId of a module that is managed by the extension producer
  • definitionStatusId is set to state whether the concept is primitive or fully defined
Description

A description of type of

Concept
ShowPartsterm
t900000000000003001 |Fully specified name|
 and at least one description of type of
Concept
ShowPartsterm
t900000000000013009 |Synonym|
 is added.

For more information on creating descriptions, please refer to 5.4.23.1 Add Description in an Extension

Stated Relationship

At least one

Concept
ShowPartsterm
t116680003 |Is a|
 relationship to a parent concept is added. Note that concepts may have more than one
Concept
ShowPartsterm
t116680003 |Is a|
 relationship as SNOMED CT is polyhierarchical.

Optionally, one (or more) attribute relationship is added. The principles for adding these relationships are similar to that of adding the required subtype relationship.

Please refer to 5.4.34.1 Add Relationship in an Extension for more information about adding relationships.

Language Refset

The new descriptions of the concept are referenced in at least one language refset to indicate language preferences.


...