Databases based on the relational model can be distributed, ‘post-modern’ as this guy puts it, too.

There’s some interesting work by logician/comp-sci/AI folks in this area, applying epistemic (and other modal) logics to multi-agent knowledge base scenarios, but I think it got a bit forgotten about because of its association with AI (think: lots of robots going around gathering knowledge which may or may not be consistent with eachother) rather than more mundane things like distributed relational databases.

Here’s a course I remember taking on the subject, which might interest anyone who thinks ‘post-modern’ databases or models of knowledge are interesting: http://web.comlab.ox.ac.uk/teaching/courses/multiagent/index.html

Perhaps a more pertinent problem with Dr. Hipp’s characterization is that it only applies to systems based on eventually consistent replication. SimpleDB, Dynamo, and Cassandra allow updates in different locations and replicate them across copies. Given enough time the copies become consistent but in the meantime different observers can get incommensurable answers to queries depending on where they are located. By contrast, databases like MongoDB use master/slave replication, which means updates occur in a single frame of reference. Observers at different locations may still get different answers to queries, but these are effectively from a single serialization history at different points in time.

If you are looking for a less inflammatory way to summarize the differences, the important distinction therefore seems to be whether or not your data are globally serialized.

> The possibility of such divergent local views is most often and most accurately compared to relativity

It’s not to say that there is no objective reality, merely that since our observations of reality must be subject to relativity then how could our modeling of reality be any different?

See http://constc.blogspot.com/2009/03/relativity-of-simultaneity.html