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Reference Set Types

This section describes four categories of reference set types, each of which contain several sub-types.

Each reference set type follows a pattern and that pattern is also represented in a machine readable form using a set of members (known as a Descriptor Template, for short). In most case, the same pattern may be used to define a number of different reference sets to serve a variety of purposes. However, there are also some highly specific reference set types that exist for a single specified purpose. These are the , and .

In each subsection, a reference set type is described under the following subheadings:

The purpose of the reference set;
The format of the reference set member record is detailed in a table;
The metadata supporting the reference set;
The machine readable reference set descriptor member records for the reference set type;

Content Reference Sets

Simple Reference Set

Purpose

A |Simple type reference set| allows a set of components to be specified for inclusion or exclusion for a specified purpose. This type of reference set represents an extensional definition of a subset of SNOMED CT components. Thus it can be used to fully enumerate a subset of concepts, descriptions or relationships.

See also Query specification reference set, which can be used to represent an intensional definition of a subset of SNOMED CT components. In an intensional definition, the members of the subset are specified by rules rather than by enumerations (e.g. all subtypes of a specified concepts).

Reference Set Data Structure

A Simple Reference Set does not have any additional fields.

Simple Reference Set - Data Structure

Field

Data type

Purpose

Mutable

PK*

Simple References Sets are subtypes of in the metadata hierarchy.

Simple Reference Sets in the Metadata Hierarchy

The table below shows the descriptor for a specific reference set that follows the pattern.

Refset Descriptor rows for the Simple Reference Set Type

refsetId

referencedComponentId

attributeDescription (Attribute description)

attributeType (Attribute type)

attributeOrder (Attribute order

Example Data for a Simple Reference Set

refsetId

referencedComponentId (Referenced component)

Attribute Value Reference Set

Purpose

An 900000000000480006 | Attribute value type reference set| allows a value from a specified range to be associated with a component. This type of reference set can be used for a range of purposes where there is a requirement to provide additional information about particular concepts, descriptions or relationships. For example, an |Attribute value type reference set| is used to indicate the reason why a concept has been inactivated.

Data Structure

An Attribute value reference set is a component reference set used to apply a tagged value to a SNOMED CT component. Its structure is shown in the following table.

Attribute Value Reference Set - Data Structure

Field

Data type

Purpose

Mutable

PK*

The metadata concepts shown below are examples of concepts that identify attribute value reference sets.

Attribute Value Reference Sets in the Metadata Hierarchy

^{_{< Not currently used}}

Concept Inactivation Values (with usage notes referring to the International Release)

^{_{< New introduced 2017-07-31}} ^{_{< NEVER used for descriptions in the International Release - may have been used in extensions}}

Description Inactivation Values (with usage notes referring to the International Release)

^{_{< New introduced 2017-07-31}} ^{_{< New introduced 2017-07-31}} ^{_{< NOT used for description inactivations after 2010-07-31}} ^_< ^{_{NOT used for description inactivations before 2016-07-31 or after 2017-07-31}} ^_< ^{_{NOT used for description inactivations before 2016-07-31 or after 2017-07-31}} ^{_{< NOT used for description inactivations before 2008-07-31 or after 2017-07-31}} ^{_{< NEVER used for descriptions in the International Release - may have been used in extensions}}

The tables below show the descriptors that define examples of reference sets that follow the pattern.

Refset Descriptor Rows for the Concept Inactivation Indicator Reference Set

refsetId

referencedComponentId (Referenced component)

attributeDescription (Attribute description)

attributeType (Attribute type)

attributeOrder (Attribute order)

Refset Descriptor Rows for the Description Inactivation Indicator Reference Set

refsetId

referencedComponentId (Referenced component)

attributeDescription (Attribute description)

attributeType (Attribute type)

attributeOrder (Attribute order)

Sample Rows from the Concept Inactivation Indicator Reference Set

refsetId

referencedComponentId (Referenced component)

valueId (Concept inactivation value)

Component Inactivation Reference Sets

The active field of each component version indicates whether a component is active or inactive. However, it does not provide any information about why a concept or description has been inactivated. The reason why a concept or description has been inactivated is indicated by a row in a component Inactivation reference set. The reason for inactivation may determine the appropriate way to deal with data in existing records, protocols or queries that use a concept or description after it has been inactivated.

The two component inactivation Reference Sets are shown in the table below.

Component Inactivation Reference Sets

Reference Set Id and Name

Note

The reason for inactivation is specified by a concept enumeration.

The permitted values for this enumeration for a concept are documented in the Editorial Guide pages on Concept Inactivation, and the type of historical association that should be applied is also provided.

Additionally, the inactivation reasons that may be stated for description inactivation are documented in this page: Description Inactivation

Related Links

See also the formal specification of .

Association Reference Set

Purpose

An 900000000000521006 |Association type reference set| represents a set of unordered associations of a particular type between components.

Data structure

An Association reference set is a reference set used to represent associations between components. Its structure is shown in the following table.

Association Reference Set - Data Structure

Field

Data type

Purpose

Mutable

PK*

The following metadata supports this reference set:

Association Reference Sets in the Metadata Hierarchy

- this has many subtypes

See for an example of the reference set description and data representation in an association type reference set.

Query Specification Reference Set

A allows a serialised query to represent the membership of a subset of SNOMED CT components. A query contained in the reference set is run against the content of SNOMED CT to produce a subset of concepts, descriptions or relationships. The query is referred to an intensional definition of the subset. It can be run against future releases of SNOMED CT to generate an updated set of subset members.

The members of the resulting subset may also be represented in an enumerated form as a Simple reference set. An enumerated representation of a subset is referred to as an extensional definition.

A Query Specification Reference Set is a String reference set containing query that represent intensional definitions of subsets of components. The result of running the query is an extensional representation of the subset of components which can be represented as a Simple Reference Set. Its structure is shown in the following table.

Query specification reference set - Data structure

Field

Ordered Component Reference Set

Purpose

An |Ordered component type reference set (foundation metadata concept)| allows a collection of components to be defined with a specified order. This type of reference set is therefore useful for creating ordered lists and to specify groups where the components that belong to the same group share the same order.

Data structure

An Ordered component reference set (an Integer Component reference set) is used to represent ordered lists and alternative hierarchies. Its structure is shown in the following table.

Ordered component reference set - Data structure

Field

Data structure

Purpose

Mutable

PK*

The following metadata in the "Foundation metadata concept" hierarchy supports this reference set:

Ordered Component Reference Sets in the Metadata Hierarchy

The tables below show the descriptor that defines the structure of the Ordered component type reference set pattern and an example of descriptor for a specific reference set that follows this pattern.

Refset Descriptor rows for an ordered reference set

refsetId

referencedComponentId

attributeDescription

attributeType

attributeOrder

Rational ordering of finger concepts using an ordered component reference set

refsetId

referencedComponentId

order (Attribute order)

Postcoordinated Expression Type Reference Set

Purpose

A 1119417006 |Postcoordinated expression type reference set (foundation metadata concept)| provides a standardized way to represent postcoordinated expressions. This representation is useful for the implementation of a postcoordinated expression repository.

Data structure

A 1119460002 |Postcoordinated expression type component (foundation metadata concept)| is a type of |Reference set (foundation metadata concept)| .

Postcoordinated expression type reference set reference set - Data structure

Field

Data type

Purpose

Mutable

PK*

The following metadata hierarchy supports this reference set:

Postcoordinated expression type reference set reference set in the Metadata Hierarchy

The tables below show the descriptor that defines the reference sets that follows the data structure of the .

Refset Descriptor rows for the postcoordinated expression type reference set.

refsetId

referencedComponentId

attributeDescription

attributeType

The International Edition of SNOMED CT includes two different types of the . These are the and . Both of these reference sets provide a standardized way of representing different types of SNOMED CT expressions, and are useful for the implementation of a postcoordinated expression repository.

The provides a standardized way to represent postcoordinated expressions as they were captured by the users, but in a canonical form. The provides a standardized way to represent postcoordinated expressions in a classifiable form. The classifiable form is a syntactically valid and concept model compliant representation of the close-to-user form expression, and serves as the input to the classifier, enabling compositional expressions to be classified with SNOMED CT content.

Map Reference Sets

Simple Map from SNOMED CT Reference Set
Simple Map to SNOMED CT Reference Set
Complex and Extended Map from SNOMED CT Reference Sets
Map to SNOMED CT with Correlation and Origin Reference Set

Simple Map to SNOMED CT Reference Set

Purpose

A 1187636009 |Simple map to SNOMED CT type reference set| supports the representation of simple maps from values in other code systems to SNOMED CT concepts. No constraints are put on the number of SNOMED CT concepts mapping to by a particular code. However, this type of reference set is usually only appropriate where there is a close "one-to-one" mapping between the coded values in another code system and SNOMED CT concepts.

Data structure

A 1187636009 | Simple map to SNOMED CT type reference set| is a String Reference Set used to represent maps from codes in another terminology, classification or code system to SNOMED CT concepts. Its structure is shown in the following table.

Simple map to SNOMED CT reference set - Data structure

Field

Data type

Purpose

Mutable

PK*

The following metadata hierarchy supports this reference set:

Simple Map to SNOMED CT Reference Sets in the Metadata Hierarchy

The tables below show the descriptors that define examples of reference sets that follow the pattern.

Refset Descriptor rows for Simple map to SNOMED CT type reference set

refsetId

referencedComponentId (Referenced component)

attributeDescription (Attribute description)

attributeType (Attribute type)

attributeOrder (Attribute order)

Sample Content from a Simple Map to SNOMED CT Reference Set

refsetId

referencedComponentId (mapTarget)

mapSource

Simple map with correlation from SNOMED CT to SNOMED CT type Reference Set

A supports the representation of simple maps from SNOMED CT concepts to SNOMED CT concepts. No constraints are put on the number of SNOMED CT concepts to which each SNOMED CT concept is mapped.

A is a Component - Component reference set used to represent maps from SNOMED CT concepts to SNOMED CT concepts. Its structure is shown in the following table.

Simple map with correlation from SNOMED CT to SNOMED CT type reference set - Data structure

Field

Data type

Purpose

Metadata Reference Sets

Description Format Reference Set

The specifies the text format and maximum length of each supported description type. This permits additional description types to be specified in future in addition to the three existing description types ( synonym, fully specified name and textual definition).

The is a C-I ( component- Integer) reference set which is used to specify the length and format of the terms in descriptions of this description type. Its structure is shown in the following table.

Description format reference set - Data structure

Field

Data type

Purpose

Mutable

MRCM Module Scope Reference Set

An specifies the set of MRCM reference sets that should be applied to the content in each module. Within a SNOMED CT Edition, the MRCM rules applied to the included modules must be consistent, to ensure data integrity within an edition is maintained.

An is structured as shown in the following table.

Field

Data type

Purpose

Mutable

PK*

Module Dependency Reference Set

Purpose

The |Module dependency reference set| represents dependencies between different SNOMED CT release modules. In each case, the dependency indicates which targetEffectiveTime of each particular module a given sourceEffectiveTime of the dependent module requires.

Data structure

The 900000000000534007 |Module dependency reference set| is a String - String reference set which is used to represent dependencies between modules, taking account of module versioning. Its structure is shown in the following table.

Field

Data type

Purpose

Mutable

PK*

Each row in the release files for components and reference set members has a . This refers to the module that the component is maintained in. Each module is either part of the SNOMED International Release or part of a single SNOMED CT Extension. The has a partition-id which indicates whether it is part of the SNOMED International Release and, if not, its namespace identifier indicates the SNOMED CT Extension that it belongs to.

A module is simply a collection of SNOMED CT components maintained as a unit by a single organization. It is the organization 's responsibility to organize the components in each extension that it is responsible for into one or more modules, in a way that best fits its business needs.

A module is represented by a descendant of in the metadata hierarchy. The immediate subtype descendants of represent groups of modules maintained by an organization and subtypes of these can be used to arrange that organizations modules into a number of groups. For example, all modules maintained by SNOMED International will be children of .

At any point in time a component must be in one, and only one module. It is possible for components and reference set members to be moved between modules (subject to constraints explained elsewhere). In this case, a new row is added to the release file with the same but with a new and a new .

Each extension must include one or more modules. Each module must be part of either the SNOMED International Release or one and only one extension. A module may not move from one extension to another over time. If components or reference set members in a module are to be moved from an extension to the SNOMED International Release or to another extension, they must either be added to an existing or newly created module maintained by the destination organization.

The does NOT represent dependencies between module. Instead, module dependencies are modeled using the .

At the point of release, if any component within a module has changed, then a new row must be added to the for each dependency of that module. The of the added rows must set to the date of the new release. The updated records indicate that some components within the module have been updated in this release. If there have been no additions, updates or inactivations of components or reference set members within a module, then a new records need not be added unless there is a requirement to declare that the unchanged module is compatible with a later release of the module(s) on which it dependents.

The recommended practice is for the column to contain the same identifier for all versions of the dependencies between the same pair of modules. This approach means that at any given time only one version of each module has effective dependencies. The dependencies of earlier versions can be reviewed by reviewing a snapshot for the effectiveTime of the earlier release.

The effectiveTime of at least one row for each pair of modules should be the same as the sourceEffectiveTime. Otherwise, there will be a period of time when a snapshot view will not show the dependencies. However, it is theoretically possible for an additional row to be added with a later effectiveTime in cases where an otherwise unchanged release of an extension, declares itself to be compatible with an updated release of the target module (in this case the effectiveTime and targetEffectiveTime are changed but the sourceEffectiveTime remains unchanged.

A module dependency only needs to be inactivated if the dependency is found to be erroneous. This is because, the module dependency is specific to a particular version of the source and target module. Therefore, if that dependency was valid at the outset it remains valid indefinitely in respect of those specified module versions, even if the dependencies between subsequent versions differ.

Module version dependencies are represented using a single . Thus all module dependency rows have the same refsetId ().

It is the responsibility of the organization owning and maintaining a dependent module to identify all modules on which it depends. They do this by adding rows to the within the dependent module. Because these added member must be in the dependent module, the moduleId of the reference set member record is also the identifier of the dependent (source) module.

The column not only indicates that this reference set member is in the specified module, it also indicates that this is the module that is the source of the dependency. As a result, in this reference set the moduleId column is immutable (i.e Mutable=NO). This is an exception to the usual rule and implies that a member of this reference set cannot move from one module to another.

The target module on which the source module depends is identified by the . Like the source module this is also immutable and this implies that if a module ceases to be dependent on another module, a new row inactivating the dependency can be added but the same member cannot be used to represent a different dependency (even if that dependency is a direct replacement of the inactivated dependency). However as noted above,

A module version may depend on one or more other module versions, and many module versions may have a dependency on a single module version. Cyclic module version dependencies are not allowed. If module-A depends on module-B, then module-B cannot depend on module-A.

Dependencies are not transitive and this means that dependencies cannot be inferred from a chain of dependencies. If module-A depends on module-B and module-B depends on module-C, the dependency of module-A on module-C must still be stated explicitly.

Any release should consist of a set of module versions that are certified as being compatible. Each release should also identify other module versions that it is dependent on even when these are outside the scope of the release. For example, the dependencies of modules in an Extension on the International Release must be stated.

Dependencies are specified between module versions, not just dependencies between modules. Therefore, it is possible to specify a dependency from a module released on one date to an earlier version of another module. The version of the dependent module is specified by the and the version of the module on which it depends is specified by the .

The following metadata in the "Foundation metadata concept " hierarchy supports this reference set

The table below shows the descriptor that defines the structure of the .

refsetId

referencedComponentId (Referenced component)

attributeDescription (Attribute description)

attributeType (Attribute type)

attributeOrder (Attribute order)

Example : The table below holds example entries for the in a snapshot view of the January 2014 SNOMED CT International Release .

This SNOMED CT International Release contains three modules:

which has no dependencies;
which depends on the ; and
which depends on both the other modules.

In this case all the 2014-01-31 modules depend on 2014-01-31 versions of the other modules. However, in some case a module may depend on an earlier version of another model (e.g. an extension module may be releases after the SNOMED CT International Release to which it applies).

Dependencies are not transitive. The fact that is dependent on may seem to imply a dependency on . However, in practice all dependencies must be explicitly specified, not just immediate dependencies.

moduleId

refsetId

referencedComponentId (Dependency target)

sourceEffectiveTime (Source effective time)

targetEffectiveTime (Target effective time)

Complex and Extended Map from SNOMED CT Reference Sets

Purpose

A 447250001 |Complex map from SNOMED CT type reference set| supports the representation of maps where each SNOMED CT concept may map to one or more codes in a target scheme. This type of reference set supports the general set of mapping data required to enable a target code to be selected at run-time from a number of alternate codes. It supports target code selection by accommodating the inclusion of machine readable rules and/or human readable advice. An 609331003 |Extended map from SNOMED CT type reference set| adds an additional field to allow the categorization of maps.

Data structure

A 447250001 |Complex map from SNOMED CT type reference set| is an Integer - Integer - String - String - String - Component reference set. The pattern is currently used for the map to ICD-9-CM. Its structure is as shown in the following table, with one exception - the table below includes an additional field (mapCategoryId) which is not used for this type of map.

An 609331003 |Extended map type reference set (foundation metadata concept)| follows the same pattern but adds one additional column. It is an Integer - Integer - String - String - String - Component - Component reference set and this pattern is currently used for maps to ICD-10. Its structure is shown in the following table, and includes the mapCategoryId.

Table: Complex and Extended map from SNOMED CT type reference sets - Data structures

Field

Data type

Purpose

Mutable

PK*

Values for are allocated on a sequential basis (for each refsetId and referencedComponentId combination) during authoring starting at 1. However, distributed mapGroup are not necessarily sequential, as some mapGroup may be created and removed during a mapping process between releases. For maps where each SNOMED CT concept only maps to at most one of a group of alternate target codes, the mapGroup field are usually be set to '1'.

Values for will be allocated on a sequential basis (within each map group) starting from '1'. For maps that do not require run - time alternatives, the mapPriority field is set to '1'.

The and fields enable run-time selection (within vendor's software) from a number of alternative map records within a mapGroup. Where there are no alternatives maps these columns of the release files will be empty (zero length string). Where alternative maps exist one or both of columns will be populated where relevant information is available.

Where both fields are populated, and a vendor's system is capable of processing a machine readable rule, this should take priority over the human readable advice. Where neither field is populated, a vendor's system should allow the end-user to select the appropriate target code from the alternates.

For more details on this topic in relation to the ICD-10 maps released as part of the SNOMED CT International Edition please see the .

The specific grammar and content of the rules for resolving complex mapping cases depends on the nature of the target code system or classification. In general, each map is accompanied by a rule which is tested against other data and can be evaluated to return one of the following values:

True - in which case the map target applies;
False - in which case the map target does not apply;
Indeterminate - in cases where there is insufficient accessible data to determine whether the map target applies. In this case manual resolution of the map using the map advice provided will be required.

The mapping rules assume access to a number of variables, that can be bound to appropriate attributes in the vendor's system information model. These include the age and gender of the patient and information about coexisting situations (e.g. records of other disorders, procedures or events in the same patient record).

Detailed definitions of the mapping rules used forms part of individual specifications for maps to particular target code systems and classifications. This will initially be provided separately and will accompany the release of the relevant mapping files. For example, the set of rules used for mapping to ICD-10 are included in the .

The following metadata supports this reference set:

List: Complex and Extended Map from SNOMED CT References Sets in the Metadata Hierarchy

The tables below examples of the descriptors for specific reference sets that follow the and patterns.

Table: Refset Descriptor Rows for a Complex Map from SNOMED CT Reference Set

refsetId

referencedComponentId (Referenced component)

attributeDescription (Attribute description)

attributeType (Attribute type)

attributeOrder (Attribute order)

Refset Descriptor Rows for an Extended Map from SNOMED CT type Reference Set

refsetId

referencedComponentId (Referenced component)

attributeDescription (Attribute description)

attributeType (Attribute type)

attributeOrder (Attribute order)

Sample Content from an Extended Map from SNOMED CT Reference Set

refSetId

referencedComponentId (Map source concept)

mapGroup (Map group)

mapPriority (Map priority)

mapRule (Map rule)

mapAdvice (Map advice)

mapTarget (Map target)

correlationId (SNOMED CT source code to target map code correlation value)

mapCategoryId (Map category value)

Reference Set Types

Content Reference Sets

Simple Reference Set

Purpose

Reference Set Data Structure

Attribute Value Reference Set

Purpose

Data Structure

Component Inactivation Reference Sets

Association Reference Set

Purpose

Data structure

Query Specification Reference Set

Ordered Component Reference Set

Purpose

Data structure

Postcoordinated Expression Type Reference Set

Purpose

Data structure

Map Reference Sets

Simple Map to SNOMED CT Reference Set

Purpose

Data structure

Simple map with correlation from SNOMED CT to SNOMED CT type Reference Set

Metadata Reference Sets

Description Format Reference Set

MRCM Module Scope Reference Set

Component Inactivation Reference Sets

Metadata Reference Sets

Content Reference Sets

Association Reference Set

Purpose

Data structure

Simple Reference Set

Purpose

Reference Set Data Structure

Map Reference Sets

Reference Set Types

Metadata

Example Descriptors and Data

Metadata

Reference Set Descriptor and Example Data

Descriptor Template

Example

Postcoordinated Expression Type Reference Set

Purpose

Data structure

Ordered Component Reference Set

Purpose

Data structure

Simple Map to SNOMED CT Reference Set

Purpose

Data structure

Attribute Value Reference Set

Purpose

Data Structure

Description Format Reference Set

Simple map with correlation from SNOMED CT to SNOMED CT type Reference Set

Query Specification Reference Set

MRCM Module Scope Reference Set

Metadata

Reference Set Descriptor and Example Data

Descriptor Template and Examples

Postcoordinated Expression Type Reference Set Examples

Metadata

Reference Set Descriptor and Example Data

Descriptor Template

Ordered reference set example

Metadata

Reference Set Descriptor and Example Data

Descriptor template and examples

Refset Examples

Metadata

Reference Set Descriptor and Example Data

Descriptor Template

Purpose

Data structure

Metadata

Reference Set Descriptor and Example Data

Descriptor