"I’ve been designing relational databases since the mid 80’s. My conclusion is that the relational model is weak and lacking. Specifically, the foreign key – that simple DRI constraint which is the keystone of the relational model - is insufficient. The model poorly represents reality."

Now, I should note before you think I am trying to incite you to go grab a pitchfork and meet me at his house with an effigy and a bottle of lighter fluid, let's get something straight.  Paul is a good guy and a friend of the relational model and SQL Server specifically.  I agree with his points for the most part, but this could be an interesting conversation, and possible an interesting series of posts:

Why the Relational Model is Insufficient (part 1)http://sqlblog.com/blogs/paul_nielsen/archive/2006/12/18/430.aspx

I left my 2 cents worth as a comment, please add your comments. 

crossposted to: http://drsql.spaces.live.com