Retrieves the columns defines as making up this secondary tables primary key. Each entry should have
a corresponding entry in the foreign-key columns described by the ForeignKeyContributingSource
aspect of this contract.
Returns:
The columns defining the primary key for this secondary table
Is "cascade delete" enabled for the foreign key? In other words, if a record in the parent (referenced)
table is deleted, should the corresponding records in the child table automatically be deleted?