All right, thank you all for your time !

I have code that uses temporary tables in at least 30 places in my programs. This is the way I did complicated queries. Most of these procedures are written 10 years ago (Interbase, Firebird 1.0). I cannot change everything (replace every query that uses temporary tables), cannot do this without proper testing. 

In the first phase I changed every field definiton of these temporary tables, defined my domains 

Integer -> MyIntegerDomain

and changed the definition (DDL) of the temporary tables in my code. 

I sure will change the code / queries that uses those temporary tables. 

Tiberiu