Re: Which normal form is this violating?

>> I have wondered about this one. Does the theory really say that
you are
not allowed two relations in a relational database that differ only by name? <<

Codd had a big hate for redundant duplicates of all kinds. His phrase was something to the effect that "if I tell you a fact twice does that make it more true?" In the case of sets, how many sets of all integers are there? One.

>> Such a restriction also suggests that it is not a good idea to
allow two
relvars that are identical in all but name in a database. They would need
to be restricted from ever containing the same relation. <<

It is suspect, but not always wrong. You can have the same structure for totally different relations -- any look up table with a code number and a character string definition.

>> Is the getout clause to use different attribute names? E.g.
 

CREATE TABLE Managers ( Manager_id Type: employee_identifer); CREATE TABLE Grunts ( Grunt_id Type: employee_identifer); <<

If they are logically different sets, then it is okay and the attribute ought to keep the same name in the entire schema. Now we can start to get into supertypes and subtypes, etc. Received on Tue Apr 30 2002 - 00:19:17 CEST