OMOP/Documentation/CommonDataModel_Wiki_Files/StandardizedVocabularies/CONCEPT_RELATIONSHIP.md

The CONCEPT_RELATIONSHIP table contains records that define direct relationships between any two Concepts and the nature or type of the relationship. Each type of a relationship is defined in the RELATIONSHIP table.

Field	Required	Type	Description
concept_id_1	Yes	integer	A foreign key to a Concept in the CONCEPT table associated with the relationship. Relationships are directional, and this field represents the source concept designation.
concept_id_2	Yes	integer	A foreign key to a Concept in the CONCEPT table associated with the relationship. Relationships are directional, and this field represents the destination concept designation.
relationship_id	Yes	varchar(20)	A unique identifier to the type or nature of the Relationship as defined in the RELATIONSHIP table.
valid_start_date	Yes	date	The date when the instance of the Concept Relationship is first recorded.
valid_end_date	Yes	date	The date when the Concept Relationship became invalid because it was deleted or superseded (updated) by a new relationship. Default value is 31-Dec-2099.
invalid_reason	No	varchar(1)	Reason the relationship was invalidated. Possible values are 'D' (deleted), 'U' (replaced with an update) or NULL when valid_end_date has the default value.

Conventions

No.	Convention Description
1	Relationships can generally be classified as hierarchical (parent-child) or non-hierarchical (lateral).
2	All Relationships are directional, and each Concept Relationship is represented twice symmetrically within the CONCEPT_RELATIONSHIP table. For example, the two SNOMED concepts of 'Acute myocardial infarction of the anterior wall' and 'Acute myocardial infarction' have two Concept Relationships: 1- 'Acute myocardial infarction of the anterior wall' 'Is a' 'Acute myocardial infarction', and 2- 'Acute myocardial infarction' 'Subsumes' 'Acute myocardial infarction of the anterior wall'.
3	There is one record for each Concept Relationship connecting the same Concepts with the same RELATIONSHIP_ID.
4	Since all Concept Relationships exist with their mirror image (concept_id_1 and concept_id_2 swapped, and the RELATIONSHIP_ID replaced by the REVERSE_RELATIONSHIP_ID from the RELATIONSHIP table), it is not necessary to query for the existence of a relationship both in the concept_id_1 and concept_id_2 fields.
5	Concept Relationships define direct relationships between Concepts. Indirect relationships through 3rd Concepts are not captured in this table. However, the CONCEPT_ANCESTOR table does this for hierachical relationships over several "generations" of direct relationships.