Snomed Ct Rf2

SNOMED CT RF2

This skill provides comprehensive guidance for working with SNOMED CT Release Format 2 (RF2) files, identifiers, and reference sets.

Quick reference

• All RF2 files: UTF-8 encoded, tab-delimited, CRLF line endings, header row with lowerCamelCase field names.
• Common fields in every file: id, effectiveTime, active, moduleId.
• Components use SCTID (6-18 digit decimal integer); reference set members use UUID.
• Release types: Full (all versions), Snapshot (most recent version only), Delta (changes since previous release).
• File naming: [FileType]_[ContentType]_[ContentSubType]_[CountryNamespace]_[VersionDate].txt

Core concepts

File format fundamentals

All SNOMED CT release files share these properties:

• UTF-8 encoded plain text.
• Tab-delimited fields.
• Each line ends with carriage return (hex 0D) followed by line feed (hex 0A), including the final line.
• First line contains lowerCamelCase column names.

For data types, common fields, the active field semantics, history mechanism, and module identification, see references/release-packages.md.

Component files

SNOMED CT has five core component file types:

1. Concept - sct2_Concept_*.txt
2. Description - sct2_Description_*.txt or sct2_TextDefinition_*.txt
3. Relationship - sct2_Relationship_*.txt or sct2_StatedRelationship_*.txt
4. Concrete Value - sct2_RelationshipConcreteValues_*.txt
5. Identifier - sct2_Identifier_*.txt

For detailed field specifications, mutability rules, primary keys, and concept enumerations for each component type, see references/component-files.md.

Reference sets

Reference sets extend the basic member format with additional columns:

• Basic format: id (UUID), effectiveTime, active, moduleId, refsetId, referencedComponentId, plus type-specific fields.
• Language refset: indicates acceptable/preferred terms for a dialect.
• Map refsets: simple map, complex map, extended map, code to expression.
• Module Dependency refset: declares inter-module version dependencies.
• Metadata refsets: reference set descriptor, description format, MRCM domains.

For reference set formats, patterns, and detailed type specifications, see references/reference-sets.md.

SNOMED CT identifiers (SCTID)

An SCTID is a 64-bit positive integer, 6-18 decimal digits, with a Verhoeff check-digit.

Structure (right to left):

1. Check-digit - 1 digit (rightmost).
2. Partition identifier - 2 digits (second and third from right).
   • 00 = Concept (international), 01 = Description (international), 02 = Relationship (international).
   • 10 = Concept (extension), 11 = Description (extension), 12 = Relationship (extension), 16 = Postcoordinated expression (extension).
3. Namespace identifier - 7 digits immediately left of partition (only for long format / extension IDs).
4. Item identifier - remaining digits left of namespace.

For check-digit computation (Verhoeff's dihedral D5), validation logic, and identifier constraints, see references/sctid.md.

Workflows

Parsing an RF2 file

1. Open the file with UTF-8 encoding.
2. Split each line on tab characters.
3. The first row contains field names in lowerCamelCase.
4. Parse effectiveTime as YYYYMMDD (or YYYYMMDDThhmmssZ for full ISO 8601).
5. Parse active as Boolean (1 = true, 0 = false).
6. For component files, id is an SCTID (parse as 64-bit integer or string).
7. For reference set files, id is a UUID (standard hyphenated hexadecimal format).

Determining the current state of a component (from a Full release)

1. Filter rows for the target id.
2. Select the row with the greatest effectiveTime less than or equal to the point in time under consideration.
3. If active = 1, the component is current and active.
4. If active = 0, the component is inactive at that point in time.
5. Do not modify or discard historical rows - they are immutable.