>>Thanks, merlin,
>>>And in that case, what is "Natural" in LineNo? I would say, with adding >>>LineNo we are creating syntethic/surrogate Key (just instead of 1 surrogate >>>column - it will be Compound key with more columns...)? The >>>same is with >>>all other tables what are "parts" of an Entity, Serial Numbers, Accounting >>>Distribution produced by Invoice...etc etc... Being the “first line” or the “second line” of a physical invoice is a property for that line. Identifying its position on the invoice is only natural. By your reasoning all identifiers are synthetically generated if you consider there is never truly only a single instance of anything in the multi-verse. The only truly unique identifier would be the time+place of an objects creation. “Hello - person born in Liverpool London, St. Whatever hospital, Room 101 @ 13:14:57AM on the 5th of March 2001 – how may I direct your call?” (I guess you could use the conception date as well although twins+ might be tough to distinguish in that case). Generally it could be argued that any well-normalized compound key is inherently natural (whether left as multiple fields or concatenated into a single field). The identifier that is assigned to the “part” individually is likely to be “synthetic” but its membership in the hierarchy naturalizes it. David J.
