The term "native XML database" (NXD) is deceiving in many ways. In fact many so-called NXDs aren't really standalone databases at all, and don't really store the XML in true native form (i.e. text). To get a better idea of what a NXD really is, let's take a look at the NXD definition offered by the XML:DB Initiative, of which the author is a participant.
A native XML database...