Let SQL drive the XQuery workhorse (XQuery join graph isolation)
Torsten Grust, Manuel Mayr, Jan Rittinger · 2010
A purely relational account of the true XQuery semantics can turn any relational database system into an XQuery processor. Compiling nested expressions of the fully compositional XQuery language, however, yields odd algebraic plan shapes featuring scattered distributions of join operators that currently overwhelm commercial SQL query optimizers.