Relationships and Column Mappings in xRefTableRelation

xRefTableRelation has what tables are related Address → AddressCounty, but i also want to know the mapping between columns. E.g:

COUNTY → COUNTYID
COUNTRYREGIONID → COUNTRYREGIONID
STATE → STATEID
DATAAREAID → DATAAREAID

Is there another table store what columns are used in the relationship?

Thanks in advance,

Mark

Relationships are typically handled by giving a column an extended data type (can be created under Data Dictionary->Extended Data Types in the AOT), then making a relation from that data type to the table and field in question.

Can I rely on the use of extended data types for all relationships?