user_errors + DDL

Hi there,  

        The other day I stumbled onto an allusion of table 'user_errors'. After checking that it indeed exists, I began to wonder how many other default tables are there for one user? I don't have any luck with Oracle on-line manuals, and would appreciate any comments.

        Another thing, what's DDL? Which kind of SQL statements constitute DDL?   

        Thanks.                                    

-- 
					Qiao

---- all man were equal, they all came from stardust. ----