Relationships Between Files

The relationships between the records in the core files in the RF2 Release Format are depicted in the following diagram.

Figure 1. Relationships between files
Each SNOMED CT concept is held as a single row in the Concept file.Each row represents a clinical concept .
Each concept has two or more descriptions associated with it (at least one synonym and at least one Fully Specified Name). Each description is held as a single row in the Description file, and may only refer to a single concept .
Each relationship, from a source concept to a destination concept, is held as a single row in the Relationship file. The type of each relationship is defined by reference to a linkage concept, also held within the Concept file .
The most basic form of relationship is the subsumption relationship, identifying that one concept is a kind of another concept. For example, an |Outpatient procedure| |Is a| |Procedure|. All the concepts in SNOMED CT form an |Is a| hierarchy, with a parent concept connected to each child concept by an |Is a| relationship. In this hierarchy, a child concept may have more than one parent concept. The root of the hierarchy is the | SNOMED CT Concept |, which has 19 top level children, each forming its own sub-hierarchy. There are no |Is a| relationships that cross from one of these sub-hierarchies to another (e.g. from a concept in the Procedures sub-hierarchy to a concept in the Substances hierarchy .
In addition to the $$ is a $$ relationships, other relationship types are also held within the Relationship file, such as |Finding site| or |Laterality|. Relationships types are specified under the |Linkage| sub-hierarchy in the | SNOMED CT Model component | hierarchy .