anchor.diff:  STEM_TABLE,UNIT_SOURCE_VALUE,MEASUREMENT,UNIT_SOURCE_VALUE
   STEM_TABLE,VALUE_SOURCE_VALUE,MEASUREMENT,VALUE_SOURCE_VALUE
   STEM_TABLE,PERSON_ID,OBSERVATION,PERSON_ID
  +STEM_TABLE,ID,OBSERVATION,OBSERVATION_ID
   STEM_TABLE,CONCEPT_ID,OBSERVATION,OBSERVATION_CONCEPT_ID
   STEM_TABLE,START_DATE,OBSERVATION,OBSERVATION_DATE
   STEM_TABLE,START_TIME,OBSERVATION,OBSERVATION_TIME
  
positive.code: STEM_TABLE,END_DATE,CONDITION_OCCURRENCE,CONDITION_END_DATE
  STEM_TABLE,STOP_REASON,CONDITION_OCCURRENCE,STOP_REASON
  STEM_TABLE,PERSON_ID,DRUG_EXPOSURE,PERSON_ID
  STEM_TABLE,CONCEPT_ID,DRUG_EXPOSURE,DRUG_CONCEPT_ID
  STEM_TABLE,START_DATE,DRUG_EXPOSURE,DRUG_EXPOSURE_START_DATE
  STEM_TABLE,END_DATE,DRUG_EXPOSURE,DRUG_EXPOSURE_END_DATE
  
negative.code: STEM_TABLE,UNIT_SOURCE_VALUE,OBSERVATION,UNIT_SOURCE_VALUE
  STEM_TABLE,QUALIFIER_SOURCE_VALUE,OBSERVATION,QUALIFIER_SOURCE_VALUE
  STEM_TABLE,PERSON_ID,PROCEDURE_OCCURRENCE,PERSON_ID
  STEM_TABLE,ID,PROCEDURE_OCCURRENCE,PROCEDURE_OCCURRENCE_ID
  STEM_TABLE,CONCEPT_ID,PROCEDURE_OCCURRENCE,PROCEDURE_CONCEPT_ID
  STEM_TABLE,START_DATE,PROCEDURE_OCCURRENCE,PROCEDURE_DATE
  STEM_TABLE,TYPE_CONCEPT_ID,PROCEDURE_OCCURRENCE,PROCEDURE_TYPE_CONCEPT_ID
  