I’ve been implying that the short list for native XML database engine vendors should be MarkLogic, IBM, and maybe Microsoft, on the theory that Progress and Intersystems tried the market and pulled back. Well, add Intersystems to the list, and not necessarily in last place. They’ve long had a very fast nonrelational engine in Cache’. Perhaps building Ensemble on it has induced them to sharpen up the XML capabilities again.
Anyhow, while I’m not at liberty to explain more of my reasoning (i.e., to disclose my evidence) — Cache’ should be taken seriously as an XML DBMS alternative … even if I never can seem to get a proper DBMS briefing from them (which is far from entirely being their fault).