Cassandra concept

[Filip Nguyen]

Hey i have just downloaded cassandra and playing with it. It's kinda new thing 
for me (i always used relation dbs). I've read most of the material on wiki 
(including referenced) and I am puzzled why there is maximum of 3 dimensions 
(super column family - super column - columns)? who came up with 3? Why not 4 or 
5 or N dimensions?

Filip