Symmetric and Asymmetric Relationships

For instance, a foreign key is asymmetric, its operation are not the same in both directions. A join in a SELECT statement however is symmetric, you can specify the operation in either direction and get the same result.

This can be a problem when you need to validate asymmetric data against symmetric. Data entered into the more lax situation may be reversed so that it fails to match into the stricter source. For example, a data dictionary specifies that TAB_CHILD has a foreign key against TAB_PARENT, but a user defining a view puts in TAB_PARENT joining to TAB_CHILD.

The answer I came up with is to produce a UNION view of the foreign keys table with itself, where the 2nd copy has the keys reversed, something like this:

SELECT table_id,table_id_par FROM foreign_keys UNION ALL
SELECT table_id_par,table_id FROM foreign_keys