Ummm...I doubt that the science of taxonomy is going to be adding too many levels in the near future.
The ordering of kingdom, phylum, etc., has been around for a LOOOOONNNNNG time now, and if anybody made changes to it, it would disrupt a whole lot more than this database.
And I disagree about using the numeric field as a foreign key. His "f1" field is just fine for that purpose. It makes no sense to add another field that duplicates that (as a number). The primary key values that I showed in my ordering table--that is, the names of the taxonomic classifications--are not all that long and they form the most natural possible primary key. And thus make a great foreign key in his main table. Granted, he *could* remove the names from the main table and REPLACE them with a numeric foreign key, but all he will be saving is a few bytes per record. I don't understand this predilection so many people have with always using an auto_incremeent field as the primary key. If there is no other reasonable primary key, okay. But when there is a wonderful natural primary key like this one (taxonomic level), you should use it.
An optimist sees the glass as half full.
A pessimist sees the glass as half empty.
A realist drinks it no matter how much there is.