SNOMED CT® Release Format 1 (RF1) Guide - ihtsdo

• One Subset can be used as the basis for another Subset. The defining clauses express differences
between the base Subset and the defined Subset.
Example:
A UK English dialect Subset may be expressed as differences from an International English language
Subset.
• Members can be added to a Subset according to hierarchical Relationships.
Example:
A single defining clause can add all | is a | descendants of the Concept "Musculoskeletal procedure" to
an orthopedic specialist Subset.
Software developers who wish to use subset definition files will need to produce software that will generate
relational subset tables from a subset definition. Please contact the IHTSDO for current information as this
format evolves.
4.4.3.4. Using relational Subset tables
Any Subset Definition can be automatically converted into the relational form. However, the relational form
is release version dependent whereas some Subset Definitions may be applicable to more than one release
of SNOMED CT.
An application may use the relational form of a Subset in one of three ways:
1. As part of a run - time query to retrieve, filter or sort members of a Subset.
Example:
An SQL query with a join between the Subsets Table and a core table could be used to:
• Provide a pick list of all members of a Subset;
• Filter a search or hierarchical list so that only members of the Subset are shown;
• Order a search or hierarchical list according to the sequence specified in the Subset.
2. To pre-filter a SNOMED CT table when it is imported from a release file.
Example:
You might choose to exclude Descriptions in a language or dialect not required.
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• Care should be taken when considering the use of pre-filtering with Concepts. If SNOMED CT
data from other systems is received it will not be possible to interpret it unless the relevant Concepts
(including Concepts used directly or indirectly in a definition) are present on the system.
3. To modify the application's internal representation of Concepts or Descriptions to allow efficient application
of the Subset.
• Possible modifications include addition of flags or indexes or some type of pre-sorting of data.
• Objectives of this include:
• Optimizing frequently used Subsets
• Facilitating rapid switching between different Subsets depending on context or user configuration.
Note: The release file formats are tab-delimited files that allow the information to be imported to any
relational database management system.
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