Objective
The objective of this service is to validate a CTU expression and transform it into a classifiable form (CF) which can be used as input to the Description Logic classifier.
Description
This service involves both the validation and transformation of a CTU expression. Three types of validation are required, including syntactic validation, content validation, and MRCM validation. For expressions not fully compliant with the MRCM, a transformation is required to generate the classifiable form.
Syntactic Validation
The syntactic validation is performed to determine if the expression conforms to the SNOMED CT compositional grammar syntax (see Compositional Grammar - Specification and Guide section 7.2 Parsing).
Please refer to the Compositional Grammar - Specification and Guide (section 7.3 Validating) for more details on the validation of expression, and the Machine Readable Concept Model for details on the computer processable concept model rules.
Content Validation
The content validation is performed to determine if all concept references included in the expression exists and are active in the version and edition of SNOMED CT which is the substrate for the given expression repository.
MRCM Validation
The MRCM validation is performed to determine if the expression complies to the concept model rules as expressed in the SNOMED CT Concept Model and specified by the machine readable concept model (the version of the MRCM applying to the version and edition of SNOMED CT which is the substrate for the given expression repository)
An expression that does not conform to the concept model cannot be relied upon to correctly classify. Therefore, it cannot be reliably tested for subsumption by another concept or inclusion in (or exclusion from) the results of an expression constraint or analytics query.
Specific terminology services required to support MRCM validation are described in the general Terminology Services Guide here: SNOMED CT concept model
Transformation
Expressions that are fully compliant with the Machine Readable Concept will not need a transformation to be represented in the classifiable form. This means that for fully MRCM compliant expressions the close-to-user form and the classifiable form of the expression are the same.
An expression may be invalid when tested against the concept model but may contain refinements that would be valid if correctly structured. There are several situations where predictable structural adjustments enable a valid expression to be constructed from an informal expression that does not fully conform to the concept model.
Examples include:
- Moving a loose attribute to an attribute group in which it is valid
- Moving a loose attribute so it provides a nested refinement to the value of another attribute
A loose attribute is an attribute that is included in the refinement of an expression without being placed in a group, although the concept model rules require it to be grouped.
The extent to which a terminology server supports the transformation of non-MRCM compliant expressions into MRCM-compliant expressions may vary between terminology servers. Each terminology server should, therefore, clearly state the level of transformations supported for expressions that are not fully MRCM compliant. A recommended practice for this it to support an API call by which it is possible to determine the transformation level. For more detail on these levels, see 5.3 Implementation
Workflow
The logical process of the service to transform and validate an expression is illustrated in the diagram below.
Summary
| Service | Description | Input Parameters | Response |
|---|---|---|---|
Validate and transform expression | Check that the CTU is syntactically valid and conforms to the concept model rules, or allowed rules for postcoordination. Transforms the close-to-user form expression to a classifiable form | - id: a unique reference to the expression repository - expId: CTU expression or expression id | Success: True Failure: False, with validation error indication |
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