Until recently, Xenomorph has been using a proprietary model to store data. However, reading in the latest Wilmott magazine (January 2008 - "Spreading Wings"),

(article should appear here at some point)

http://www.xenomorph.com/news/

CEO Brian Sentance talks about how Xenomorph are working with Microsoft to store the data on SQL Server. It will be interesting to see what performance can be achieved in the relational world (assuming that is how it is implemented).

On a related note, SQL Server is falling down the rankings on the TPC-C league

http://www.tpc.org/tpcc/results/tpcc_perf_results.asp?resulttype=noncluster

if SQL 2008 offered any tangible performance improvements I would have expected to see an entry by now

There are new records in other areas

http://blogs.msdn.com/sqlperf/archive/2008/02/27/sql-server-2008-launched-today-with-great-performance-amp-scalability.aspx

http://www.tpc.org/tpce/tpce_perf_results.asp

but could this be down to hardware improvements? Furthermore, the absence of competing databases implies that other vendors don't take this as seriously