XSLT and XPath Optimization
Michael Kay · 2004
Recent releases of Saxon support XQuery 1.0 as well as XSLT 2.0. However, the XQuery processor is an in-memory processor, not a database query engine. Optimizing database queries is an entirely different art, because it relies so heavily on rearranging queries to exploit persistent indexes. An in-memory processor does not have this opportunity, because the only indexes available are those that are constructed transiently for the duration of a transformation or query.