SNOMED CT Concept Model

The SNOMED CT Concept Model is a set of rules that govern the ways in which SNOMED CT concepts are permitted to be modelled using relationships to other concepts. These rules are critical to the consistent modelling of SNOMED CT content, which in turn determines the extent to which reproducible logical inferences can be drawn. These logical inferences are the foundation for effective use of SNOMED CT for retrieval and reuse of clinical information. 

For each attribute (relationship type) defined in SNOMED CT, the concept model specifies a set of rules to support the proper application of SNOMED CT attributes, including:

• Attribute Domain: The set of concepts to which the attribute may be applied
• Attribute Range: The set of concepts which may be used as the value for the attribute
• Attribute Cardinality: The minimum and maximum number of times that the attribute may appear in a concept definition
• Attribute Grouping:  Whether an attribute may or may not belong to a relationship group
• Attribute In-group cardinality: The minimum and maximum number of times that the attribute may appear in each relationship group

Machine Readable Concept Model 

The Machine Readable Concept Model (MRCM) represents rules of the SNOMED CT concept model in a form that can be read by a computer and applied to test that concept definitions and expressions comply with the rules. 

Table 2.3-1 shows a few example of concept model rules, as they can be derived from the MRCM reference sets.

Table 2.3-1: Example of concept model rules.

Examples of Use

Given the machine processable nature of SNOMED CT, the Compositional Grammar and the MRCM, postcoordinated expressions may be tested against the rules specified in the MRCM, for example to validate the expression, or to support the creation of MRCM-compliant expressions.

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

1. Determine which domains the expression belongs to using the  | 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  | 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  | MRCM attribute domain reference set|  for the given attribute and parent domain;
4. Determine the valid range for each attribute using the rangeConstraint in  | MRCM attribute range reference set| .

Please note that in the above process only rules with a contentType = <<  723595009 | All postcoordinated SNOMED CT content|  should be used. Rules with a ruleStrength of  | Mandatory concept model rule|  should be enforced when authoring and cause an error during validation, while rules with a ruleStrength of  | Optional concept model rule|  should be used as a recommendation for authoring and result in a warning during validation.

An alternative approach to authoring and validating postcoordinated expressions is to use the domainTemplateForPostcoordination from the  | MRCM domain reference set|  to ensure compliance with the full set of attribute rules. The domainTemplateForPostcoordination can also be specialized into an expression authoring template that meets the needs of a particular use case, while still conforming to the overall rules of the domain.

Editorial Guidance

In addition to the concept model, SNOMED International also rely on editorial principles when authoring the content of SNOMED CT. The SNOMED CT Editorial Guide covers a wide range of topics, including the principles of SNOMED CT, and the structure and organization of the terminology. In addition, it documents guidelines for the modelling of content within specific domains and sub-domains that and it defines the role of the attributes available. The SNOMED CT Editorial Guide plays a critical role in ensuring the quality of SNOMED CT content, as it documents the authoring principles that require human analysis and interactions to ensure that concepts are accurate, consistently modelled, and clinically relevant. 

Implementing postcoordination with SNOMED CT is similar to authoring SNOMED CT concepts, as it involves creating clinical meanings by combining existing concepts. However, it is crucial to ensure that the implementation of postcoordination does not impact clinical safety.

It is essential to involve relevant stakeholders such as clinicians, informaticians, and quality assurance personnel to ensure that the approach taken is appropriate and safe for use in clinical practice. Thorough testing and evaluation of the postcoordinated expressions can help identify potential safety concerns early in the implementation process, ultimately leading to safer and more effective healthcare.