For referential integrity to hold in a relational database, any column in a base table that is declared a foreign key can contain either a null value, or only values from a parent table's primary key or a candidate key.
22.
NAUI adapted the 1995 DCIEM Sports Table for use in all NAUI courses and these were used until they were replaced by RGBM based tables in 2002 . ( The NAUI recreational air tables based on RGBM model are copyrighted 2001)
23.
In any database management system following the relational model, a cached as a concrete ( " materialized " ) table ( rather than a view as such ) that may be updated from the original base tables from time to time.
24.
:: : : : This looks very much like a crying out for a base table / list that explains the issues that are being dicussed here, and also a potential for anyone with a historical bent to actually show earlier forms in such a table / list.
