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The process of transforming an

Glossary ref
expression
to a
Glossary ref
normal form
is based on the
Glossary ref
description logic
definitions of the
Glossary ref
concepts
referenced by the
Glossary ref
expression
. Using this approach,
Glossary ref
expressions
that are authored, stored and/or communicated in a relatively informal close-to-user form are logically transformed into a common normalized form. In this normalized form it is possible to apply simple rules to test subsumption between
Glossary ref
expressions
.

The simplest case of a valid close-to-user

Glossary ref
expression
is a single conceptId, and the approach described can be applied to these simple
Glossary ref
precoordinated expressions
, as well as to more complex
Glossary ref
expressions
that include multiple conceptIds and
Glossary ref
refinements
(
Glossary ref
qualifiers
).

The approach to normalization may be applied to specific

Glossary ref
expressions
but may also be extended to take account of contextual information derived from the information model in which the
Glossary ref
expression
is situated. Therefore, the
Glossary ref
normal form
may include
Glossary ref
SNOMED CT
context information, even if this is not present in the initial
Glossary ref
SNOMED CT expression
.

The algorithm extends earlier work on

Glossary ref
canonical forms
as follow:

  • Anchor
    _095badbf-969d-4bc8-9048-89cbece4a2b1__9
    _095badbf-969d-4bc8-9048-89cbece4a2b1__9
    Normalizes
    Glossary ref
    fully defined
    values within definitions or
    Glossary ref
    expressions
    producing nested
    Glossary ref
    expressions
    that are fully normalized .
  • Merges
    Glossary ref
    refinements
    stated in an
    Glossary ref
    expression
    with definitional
    Glossary ref
    relationships
    present in the definitions of the
    Glossary ref
    concepts
    referenced by the
    Glossary ref
    expression
    :
    Anchor
    _095badbf-969d-4bc8-9048-89cbece4a2b1__b
    _095badbf-969d-4bc8-9048-89cbece4a2b1__b
    • The merge process takes account of
      Glossary ref
      refinements
      that may not be grouped or nested in a manner that precisely reflects the structure of a current (or future)
      Glossary ref
      concept
      definition;
    • This avoids the need to add, store and communicate potentially spurious detail from current definitions to the
      Glossary ref
      expression
      recorded by a user or software application.
  • Takes account of context rules including default context and a preliminary approach to moodCode mapping and handling of procedures with values (present in algorithm but not yet easily visible in test environment).
  • Supports
    Glossary ref
    subsumption tests
    that take account of finding specified with
    Scg expression
    ShowPartsterm
    410516002|known absent|
    finding context.

illustrates an overview of the process of normalization of an

Glossary ref
expression
. Subsequent sections describe the processes shown in this diagram.

Anchor
_095badbf-969d-4bc8-9048-89cbece4a2b1__c
_095badbf-969d-4bc8-9048-89cbece4a2b1__c
Anchor
_095badbf-969d-4bc8-9048-89cbece4a2b1__7
_095badbf-969d-4bc8-9048-89cbece4a2b1__7

Figure 57. Overview of expression normalization process