Overview

In this chapter, we describe the logical design of the SNOMED CT MRCM.

Each SNOMED CT Module may have a concept model that is captured using a MRCM. A MRCM contains a set of domains and a set of attributes, which may be applied to one or more domains. The MRCM specifies the cardinality and valid range of each attribute, and indicates whether or not the attribute should be grouped. The domain, range, cardinality and grouped indicator for each attribute is also combined into a single 'attribute rule', which is represented using a SNOMED CT Expression Constraint. For each domain, the set of valid attributes and their associated rules are compiled into two SNOMED CT 'domain templates' – for precoordinated concept authoring and postcoordinated expression authoring respectively. These domain templates may be further specialized to support customized authoring of specific subdomains. A MRCM may also have a set of DL (Description Logic) rules.

Figure 1 below illustrates the major components of the MRCM described above.

Figure 1: Abstract Model of the SNOMED CT MRCM

Details

Figure 2 below illustrates the logical design of the SNOMED CT MRCM using a UML class diagram.

Figure 2: Logical Model of SNOMED CT MRCM

This UML class diagram illustrates that a SNOMED CT Edition may be associated with at most one MRCM, and each MRCM may be applied to one or more SNOMED CT Editions. A MRCM contains a set of domains, which are identified by a single domainId. Each domain has exactly one domainConstraint represented using a SNOMED CT Expression Constraint (which specifies the valid concepts in the domain). A domain also has a proximalPrimitiveConstraint (which specifies the domain constraint used for proximal primitive modelling in this domain), a proximalPrimitiveRefinement (which specifies any mandatory refinements that must be applied when proximal primitive modelling in this domain), a precoordinatedDomainTemplate (which provides a general template of all possible attributes that may be applied to this domain when defining a precoordinated concept), and a postcoordinatedDomainTemplate (which provides a general template of all possible attributes that may be applied to this domain when defining a postcoordinated expression).

A MRCM also contains a set of attribute rules, each associated with a specific rule strength (e.g. 'Mandatory') and content type (e.g. 'All SNOMED CT content'). An Attribute Rule may either associate an attribute with the domains to which it may be applied (i.e. an Attribute Domain Rule), or it may associate an attribute with the range of valid concepts that may be used as its value (i.e. an Attribute Range Rule).

A MRCM may also contain one or more DL rules, which specify Description Logic axioms which apply to the SNOMED CT content.