A method and apparatus for processing queries is provided. A query is received at a mid-tier node of a multi-tier system. The mid-tier node includes a mid-tier cache that is configured to cache relational tables from one or more databases managed by a database server in a database tier of the multi-tier system. At the mid-tier node, a determination is made whether the received query includes an operator for requesting data of an XML datatype from the database server, where the XML datatype is supported as a native datatype by the database server. If a determination is made that the query includes such operator, then one or more portions of one or more relational tables are retrieved from the database server and stored in the mid-tier cache. The one or more relational tables store, in the one or more portions, index information associated with the requested data of the XML datatype. The received query is rewritten into a relational query against at least the one or more portions of the one or more relational tables that are stored in the mid-tier cache.