Overview

In this section, we discuss a range of topics that were considered in the design of the SNOMED CT MRCM, including:

• How the MRCM will be authored and quality checked;,
• How the MRCM will be used to support the use cases described in Chapter 2;. Use Cases,
• How the MRCM will be versioned when corrections or enhancements are made; , and
• How the MRCM can be extended and adapted for use with SNOMED CT extensions;

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Authoring and Quality Checks

The MRCM has been designed to include minimal redundancy, to make the authoring and maintenance of these rules less error-prone. For example, by using separate reference sets to represent the attribute domains and ranges, each range does not need to be repeated for each of the attribute's domains.

To support implementers who prefer to process string-based representations of the rules, three MRCM attributes have been provided that concatenate information from other fields (as per the table below). These attributes have been populated automatically (rather than authored manually) to avoid inconsistencies between the structural and string-based representations of the rules.  

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MRCM Reference Set

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Attribute

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Autopopulated From

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MRCM domain reference set

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domainTemplateForPrecoordination

D.domainConstraint, AD.grouped, AD.attributeCardinality, AD.attributeInGroupCardinality, AR.rangeConstraint

The MRCM attributes that may be generated from other attributes are:

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WHERE D. referencedComponentId = AD.domainId AND AD. referencedComponentId = AR.domainId

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MRCM domain reference set

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domainTemplateForPostcoordination

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In addition, the quality of the international SNOMED CT MRCM is checked using a range of mechanisms, including:

• Manual review, supported by the inclusion of human-readable terms for each concept identifier in the reference sets;
• Automated testing, including checks for the following:
  • All MRCM reference sets conform to the associated Descriptor Template,
  • All concept identifiers refer to active concepts in the relevant SNOMED CT international edition,
  • All concept identifiers refer to concepts from a value set appropriate for that field,
  • All parsable strings (e.g. expression constraints) are syntactically valid (based on the associated ABNF syntax) and refer to concepts that are active in the relevant SNOMED CT international edition,
• Feedback from direct use by SNOMED International staff in the SNOMED CT authoring tools, and
• Feedback from the SNOMED CT member, vendor and user communities.

Supporting Use Cases

Another important consideration in the design of the MRCM is how it can best be used to support the range of anticipated use cases. In this section, we describe the ways in which the MRCM design supports each of the use cases presented in 2. Use Cases.

Precoordinated Content Development

As described in 2. Use Cases, one of the key use cases for the SNOMED CT MRCM is to assist with the consistent authoring and validation of SNOMED CT concepts. 

To support the authoring and validation of SNOMED CT precoordinated content, the following MRCM process can be used:

1. Identify the parents of the concept being authored;
   • Please note - Either proximal primitive parents or proximal parents may be selected, depending on the authoring approach used;
2. Determine which domains the parent concepts belong to using the 

   Concept
   ShowParts term t 723589008 |MRCM domain reference set|

   . 
   • If the proximal parent modelling approach is used, the stated parents should be tested for membership in each domain using the domainConstraint;
   • If the proximal primitive parent modelling approach is used, the stated parents should be tested for membership in each domain using the proximalPrimitiveConstraint and all required refinements in the proximalPrimitiveRefinement should match at least one defining relationship stated on the concept being authored;
     
     • Please note - If any of the proximal parents belong to a given domain, then the authored concept belongs to that domain.
     • Please note - Irrespective of the modelling approach used, the concept being authored can be tested for membership in a domain by checking if its inferred parents (i.e. after classification) are valid against the associated domainConstraint.
3. Determine the set of valid attributes for the given domains using the 

   Concept
   ShowParts term t 723604009 |MRCM attribute domain reference set|

    and allow defining relationships to be added from this set;
4. For each attribute used to define the concept, ensure that the grouping and cardinality are valid according to the rules specified in 

   Concept
   ShowParts term t 723604009 |MRCM attribute domain reference set|

    for the given attribute and parent domain;
5. Determine the valid range for each defining attribute using the rangeConstraint in 

   Concept
   ShowParts term t 723592007 |MRCM attribute range reference set|

   .

Please note that when the above process is being applied to the authoring of new precoordinated content, then only rules with a contentType 

An alternative approach to authoring and validating precoordinated concepts is to use the domainTemplateForPrecoordination from the

Other features provided by the MRCM that are helpful for precoordinated content development include:

• The 

  Concept
  ShowParts term t 723589008 |MRCM domain reference set|

   and the 

  Concept
  ShowParts term t 723604009 |MRCM attribute domain reference set|

   use domains defined in terms of a single top-level hierarchy. This enables concepts being authored to be tested for subsumption with each domain concept, using techniques that are relatively simple to implement (e.g. using a transitive closure table).

• The 

  Concept
  ShowParts term t 723592007 |MRCM attribute range reference set|

   includes a set of attribute rules that combine the domain, grouping, cardinality and range constraints into a single expression constraint, which can facilitate the efficient implementation of content validation.

• The ruleStrengthId attribute in the 

  Concept
  ShowParts term t 723604009 |MRCM attribute domain reference set|

   and the 

  Concept
  ShowParts term t 723592007 |MRCM attribute range reference set|

   allows both mandatory rules (resulting in errors) and optional rules (resulting in warnings) to be specified.

• The contentTypeId attribute in the 

  Concept
  ShowParts term t 723604009 |MRCM attribute domain reference set|

   and the 

  Concept
  ShowParts term t 723592007 |MRCM attribute range reference set|

   allows the scope of each rule to be restricted to a particular type of SNOMED CT content, including:

  • Concept
    ShowParts term t 723596005|All SNOMED CT content|

     – for rules which apply to both precoordinated and postcoordinated content;

  • Concept
    ShowParts term t 723594008|All precoordinated SNOMED CT content|

     – for rules which apply to all precoordinated content (but not to postcoordinated content);

  • Concept
    ShowParts term t 723593002|All new precoordinated SNOMED CT content|

     – for rules which apply to newly authored (i.e. stated) precoordinated content, which may not necessarily be valid for all existing content; and

  • Concept
    ShowParts term t 723595009|All postcoordinated SNOMED CT content|

     – for rules which apply to all postcoordinated content (but not to precoordinated content).

Expressions, Constraints and Queries

2. Use Cases describes using the SNOMED CT MRCM to assist the authoring and validation of SNOMED CT postcoordinated expressions, SNOMED CT expression constraints, and SNOMED CT queries. These languages allow one or more focus concepts to be defined, which when tested against a domain in the MRCM enables possible attribute refinements, cardinalities and valid ranges to be found.

To support the authoring and validation of SNOMED CT postcoordinated expressions the following MRCM process can be used:

1. Determine which domains the expression belongs to using the 

   Concept
   ShowParts term t 723589008 |MRCM domain reference set|

   • An expression belongs to a given domain if any focus concept is either:
     1. Valid when tested against the associated domainConstraint; or
     2. Valid when tested against the associated proximalPrimitiveConstraint and all required refinements in the proximalPrimitiveRefinement either match a defining relationship on the given focus concept, or match a refinement condition added to the expression being authored;
2. Determine the set of valid attributes for the given domains using the 

   Concept
   ShowParts term t 723604009 |MRCM attribute domain reference set|

    and allow refinements to be added using attribute concepts from this set;
3. For each attribute used to define the concept, ensure that the grouping and cardinality are valid according to the rules specified in 

   Concept
   ShowParts term t 723604009 |MRCM attribute domain reference set|

    for the given attribute and parent domain;
4. Determine the valid range for each attribute using the rangeConstraint in 

   Concept
   ShowParts term t 723592007 |MRCM attribute range reference set|

   .

Please note that in the above process only rules with a contentType

An alternative approach to authoring and validating postcoordinated expressions is to use the domainTemplateForPostcoordination from the 

To support the authoring and validation of SNOMED CT expression constraints and queries the following MRCM process can be used:

1. Determine which domains the constraint or query belongs to using the 

   Concept
   ShowParts term t 723589008 |MRCM domain reference set|

   • An expression constraint or query belongs to a given domain if either:
     
     1. Any focus concept is valid when tested against the associated proximalPrimitiveConstraint; or
     2. The constraint or query belongs to a parent domain of the given domain.
        
        • Please note: The concept model requirements for constraints and queries are more relaxed than those for postcoordinated expressions, because their role is to define the membership of a set of concepts or expressions, rather than restrict the manner in which a single concept or expression may be defined.
2. Determine the set of valid attributes for the given domains using the 

   Concept
   ShowParts term t 723604009 |MRCM attribute domain reference set|

    and allow refinements to be added using attribute concepts from this set;
3. For each attribute used to define the concept, ensure that the grouping and cardinality are consistent with the rules specified in 

   Concept
   ShowParts term t 723604009 |MRCM attribute domain reference set|

    for the given attribute and parent domain. In particular:
   • An attribute should only be grouped in an expression constraint or query if it specified as grouped = 1 for that domain in

     Concept
     ShowParts term t 723604009 |MRCM attribute domain reference set|

     . Any attribute can appear as ungrouped in an expression constraints.
   • A cardinality constraint used in an expression constraint or query should be the same, or stricter than the cardinality specified for the given attribute and domain in

     Concept
     ShowParts term t 723604009 |MRCM attribute domain reference set|

     .
4. Determine the valid range for each attribute using the rangeConstraint in 

   Concept
   ShowParts term t 723592007 |MRCM attribute range reference set|

   .

Please note that if the expression constraint or query is being applied to a substrate that includes only precoordinated content, then only the MRCM rules with a contentType

Natural Language Processing

The

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attributeRule

In addition, the quality of the international SNOMED CT MRCM is expected to be checked using the following mechanisms:

• Manual review, supported by the inclusion of human-readable terms for each concept identifier in the reference sets;
• Automated testing, including checks for the following:
  • All MRCM reference sets conform to the associated Descriptor Template;
  • All concept identifiers refer to active concepts in the relevant SNOMED CT international edition;
  • All concept identifiers refer to concepts from a value set appropriate for that field;
  • All parsable strings (e.g. expression constraints) are syntactically valid (based on the associated ABNF syntax) and refer to concepts that are active in the relevant SNOMED CT international edition;
• Feedback from direct use by IHTSDO staff in the SNOMED CT authoring tools;
• Feedback from the SNOMED CT member, vendor and user communities.

Supporting Use Cases

Another important consideration in the design of the MRCM is how it can best be used to support the range of anticipated use cases. In the following section, we describe the ways in which the MRCM design supports each of the use cases presented in Chapter 2.

Precoordinated Content Development

As described in Section 2.2, one of the key use cases for the SNOMED CT MRCM is to assist in the consistent authoring and validation of SNOMED CT concepts. With this in mind, the following features were included to optimize the MRCM for use in precoordinated content development:

• The

  Scg expression
  ShowParts term
  111115|MRCM domain reference set|

   and the

  Scg expression
  ShowParts term
  111115|MRCM attribute domain reference set|

   include attribute domains defined in terms of the lowest common supertype permitted in the inferred view (i.e. after classification of the concept being authored);

• The

  Scg expression
  ShowParts term
  111115|MRCM domain reference set|

   includes the proximal primitive constraints and mandatory defining relationships required to support proximal primitive modelling in each domain (in the stated view);

• The

  Scg expression
  ShowParts term
  111115|MRCM domain reference set|

   includes a general domain template, which can be used for authoring any content in the given domain using either proximal primitive modelling or proximal parent modelling authoring methods. Please note that this general domain template may be further constrained to support the specialized modelling requirements of specific subhierarchies in the given domain.

• The

  Scg expression
  ShowParts term
  111115|MRCM domain reference set|

   and the

  Scg expression
  ShowParts term
  111115|MRCM attribute domain reference set|

   use domains defined in terms of a single top-level hierarchy. This enables concepts being authored to be tested for subsumption with each domain concept, using techniques that are relatively simple to implement (e.g. using a transitive closure table).

• The

  Scg expression
  ShowParts term
  111115|MRCM attribute range reference set|

   specifies the valid set of values (rangeConstraint) for each attribute used in the authoring of precoordinated content.

• The

  Scg expression
  ShowParts term
  111115|MRCM attribute range reference set|

   also includes a set of attribute rules that incorporate the domain, grouping, cardinality and range constraints together into an expression constraint, to support the efficient implementation of content validation.

• The ruleStrengthId attribute in the

  Scg expression
  ShowParts term
  111115|MRCM attribute domain reference set|

   and the

  Scg expression
  ShowParts term
  111115|MRCM attribute range reference set|

   allows both mandatory rules (resulting in errors) and optional rules (resulting in warnings) to be specified.

• The contentTypeId attribute in the

  Scg expression
  ShowParts term
  111115|MRCM attribute domain reference set|

   and the

  Scg expression
  ShowParts term
  111115|MRCM attribute range reference set|

   allows the scope of each rule to be restricted to a particular type of SNOMED CT content, including:
  • All SNOMED CT content – for rules which apply to both precoordinated and postcoordinated content;
  • All precoordinated SNOMED CT content – for rules which apply to all precoordinated content (but not necessarily to postcoordinated content);
  • New precoordinated SNOMED CT content only – for rules which apply to newly authored precoordinated content, which may not necessarily be valid for all existing content; and
  • All postcoordinated SNOMED CT content – for rules which apply to all postcoordinated content (but not necessarily to precoordinated content).

Expressions, Constraints and Queries

Section 2.3 describes using the SNOMED CT MRCM to assist the authoring and validation of SNOMED CT postcoordinated expressions, SNOMED CT expression constraints, and SNOMED CT queries. These languages allow one or more focus concepts to be defined, which when tested against a domain in the MRCM enables possible attribute refinements, cardinalities and valid ranges to be found.

The optimizations described in section 6.3.1 for use in SNOMED CT concept authoring, can also make the authoring and validation of SNOMED CT expressions, expression constraints and queries more efficient. In addition to these general authoring features, the

111115|MRCM domain reference set|

111115|MRCM attribute range reference set|

Please note that SNOMED CT expression constraints and queries used on a substrate that includes only precoordinated content must use the MRCM rules that apply to

111115|All SNOMED CT content|

111115|All precoordinated SNOMED CT content|

111115|All postcoordinated SNOMED CT content|

111115|All SNOMED CT content|

111115|MRCM attribute domain reference set|

Natural Language Processing

In a similar way to how the MRCM can be used for postcoordinated expression authoring, the MRCM can also be used to support Natural Language Processing (NLP), as described in section 2. 4Use Cases. When terms used in the free text are associated with a particular SNOMED CT concept, this concept can be tested for subsumption against the domains in the

111115|MRCM domain reference set|

Optimizations to the MRCM rules may also be adopted by NLP implementations to simplify the testing of membership in a potential range. For example, each range constraint could be split into its separate subhierarchies to allow simple techniques, such as a transitive closure table, to be useda transitive closure table, to be used.

For more information on using SNOMED CT in Natural Language Processing, please refer to  Data Analytics with SNOMED CT.

Terminology Binding to Information Models

Section 2. 5 describes Use Cases describes using the MRCM to suggest possible SNOMED CT terminology bindings for an information model, to ensure that the bindings are consistent (at least at a high level) with the SNOMED CT concept model, and to support the design of expression templates.

The features designed to support SNOMED CT content authoring can similarly be used to support these terminology binding purposes. For example, the domainTemplateForPostcoordination could be adopted and specialized to support the terminology binding requirements of a specific information model. Similarly, new use-processes above for authoring SNOMED CT postcoordinated expressions, expression constraints and queries can similarly be applied to support terminology binding. Alternatively, new use case specific MRCM reference sets could be developed, which restrict the available attributes and ranges that may be used in a specific implementation scenario.

Versioning

As mentioned in Requirement 3. Requirements (D.5), the concept model must be able to be changed between releases to fix identified issues and enhance future releases.

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When a new or updated rule is introduced to the MRCM, it may take a period of time before all existing content conforms to the new rule. In these situations, a content type of

Extension

As described in Requirement 3. Requirements (D.6), the international MRCM rules defined by the IHTSDO SNOMED International must be able to be extended and adapted by organizations developing SNOMED CT extensions, to support the concept model requirements of their extension content.

To support this requirement, SNOMED CT extension developers will be able to copy the international MRCM rules defined by the IHTSDO SNOMED International into one or more extension MRCM reference sets and edit these reference sets to add new rules and restrict or extend the existing rules as required. New MRCM reference sets created for a SNOMED CT extension must be designed to ensure consistency and data integrity between editions. Please note that if no changes to the SNOMED CT concept model are required to support an extension, no additional MRCM reference sets need to be created, as the international MRCM can be reused by the extension.

The