The Windchill ESI Services XML output is automatically rendered by a combination of various ESI renderers, the ESI Mapper and the VDB Builder. The details of this rendering process are described in the Windchill Enterprise Systems Integration Open Application Programming Interface Guide. The function of the XML schema is to describe the format of this automatically generated output. You would typically need to modify the XML schema if you had performed customizations such as adding an attribute to a Windchill ESI service or adding a new service. See the XML schemas section of this document for details on how to modify an XML schema.