Just a small thought to share.
Oracle doesn’t really comply to the rule 11 of Codd’s 12 rules. It does have database links and tables can be grouped in different locations (databases) but it’s not possible to distribute a table transparently across several locations. MySQL Cluster, on the other hand, distributes rows of a table over different data nodes using hash function on the primary key and it’s transparent to the client so it conforms to the Rule 11 as opposed to Oracle.
By the way, if you are interested on MySQL Cluster, keep an eye on Pythian Goodies — one of the last topics was on MySQL Cluster and I believe it should be posted soon.