I plead guilty to being a zealot.  I am absolutely a zealot when it comes to proper database design because I have to deal with the consequences of poor database design on a daily basis.

Now, as to your charge that I didn't add any facts, and that Code tables present an  "elegant solution", I would ask you to provide some facts of your own.  You and others have accused me of being overly wordy, and that might be the case to some extent, but I felt that it was necessary to fully illustrate the point.  Part of my "wordiness" is due to the diffuculty in trying to deal coherently with that which is essentially incoherent.  However your overly brief statement as to the "elegance" of code tables is hardly believable since you provide no evidence (and I don't believe that you ever could) unless your brevity is to be taken for proof...

Of course hierarchical data will always be around, so what?  A properly designed relational database is perfectly capable of representing hierarchies, however, hierarchical databases (to include XML) have a very difficult time properly representing the more complex (and useful) "has a" logic for data that is not inherently hierarchical.