A method and system for modifying program applications of a legacy computer system to directly output data as XML using a DOM instance, models the legacy computer system, maps the model to an XML schema and automatically modifies one or more applications to directly output XML formatted data from an internally constructed DOM instance in cooperation with a writer engine. The writer engine allows for an arbitrary number of contexts to be simultaneously active and builds a complete DOM instance by using the multiple contexts to buffer output data. The writer engine directly loads XML schema information to construct and output DOM instances in accordance with the schema and subject to further transformation by XSLT stylesheets.