Table 1.

High-level architectural comparison of the three analyzed IDRs

PROPERTY	i2b2	OMOP	VDW
Generic fact data structure	OBSERVATION_FACT	OBSERVATION	n/a
Designated data structures	PATIENT_DIMENSION, VISIT_DIMENSION, PROVIDER_DIMENSION	PERSON, VISIT_OCCURENCE, DEATH, COHORT, PROVIDER, CARE_SITE DRUG_ERA, DRUG_EXPOSURE, CONDITION_ERA, CONDITION_OCCURENCE, PROCEDURE_OCCURENCE	DEMOGRAPHICS, CENSUS, ENCOUNTERS, ENROLLMENT, DEATH, PROVIDER, VITAL SIGNS, LAB_RESULTS, DIAGNOSES, PROCEDURES, PHARMACY, TUMOR
Terminology layer	CONCEPT_DIMENSION	CONCEPT, CONCEPT_RELATIONSHIP, CONCEPT_ANCESTOR, SOURCE_TO CONCEPT_MAP	No generic terminology table; EVER_NDC table (for drug codes only)
Fact nesting	Generic modifier_cd column (coded in native terminology) in the OBSERVATION_FACT table	Generic obs_value_as_concept_id column (coded in native terminology) in the OBSERVATION table. Domain-specific columns in designated tables. Additional fact grouping (temporal, functional) via PAYER_PLAN_PERIOD table and several _ERA tables.	No generic fact nesting structure. Numerous domain-specific columns in designated tables (e.g., encounter type in PROCEDURES). Additional fact grouping (temporal) via ENROLLMENT table.
Designated columns in fact table	valtype_cd, units_cd, encounter_num, provider_id, location, confidence_num, valueflag_cd, observation_blob	observation_type_concept_id, obs_range_low, obs_range_high, associated_provider_id, source_obs_code, unit_concept_id	n/a