Re: pervasiveness of surrogate (also called synthetic) keys

>>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 5^th 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.