Practical Guide to Postcoordination

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The authoring of postcoordinated expressions can also be performed using expression templates. These templates provide reusable patterns for the representation of expressions that express similar meanings. Expression templates can define the set of attributes and attribute values that must be used to obtain the expected classification results, and assist the users in authoring expressions in a consistent way. To ease the authoring of postcoordinated expressions using expression templates, the templates may be populated in a data entry form where the slots provide searchable fields constrained as specified by the template.

For example, there may be a preference to always represent fractures using an expression in which the body site is explicitly defined as the value of the |finding site| attribute. Given an appropriate expression template and a predefined list of body structures, a set of template-compliant postcoordinated expressions can be authored.

SNOMED International specifies the SNOMED Template Syntax, which provides the formal rules for representing slots in SNOMED CT expressions. A slot can represent a placeholder for a value that is not known at the time of authoring. These placeholders can be completed at a later time using data recorded elsewhere (such as in an information model or entered into a data entry form). Expression templates can thus be used to enable the easy and consistent creation of postcoordinated expressions from data entered into a user interface.

Example

Consider the following expression template for creating expressions representing family history disorders:

Expression Template for Family History Disorders

This template includes only one slot to capture the value of the |Associated finding| attribute, i.e. the @finding slot. All other parts of the expression are fixed to the following attributes required to represent the meaning of the described meaning:

- The temporal context, to state that the finding occur now, or in the past:

- The finding context, to state that the finding exists, opposed to being absent:
- The subject relationship context, to state that the situation relates to a person in the family:

Although this information may not be explicitly selected by the end user, this meaning may implied by the context in which it is selected, for example:

  • If the user selects an option in a pick list with a term saying "Family history of @finding", e.g. "Family history of breast cancer"
  • If the user enters a disorder from a list or search field belonging to a 'Family history' section of a user interfac

If a user selects the value  56265001 | Heart disease|  to the finding slot (e.g.  finding =  56265001 | Heart disease| ), then the following expression can be derived based on that single selection:

Resulting Expression


Detailed information about the template syntax can be found here: SNOMED Template Syntax 

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