10. A computer implemented method to query data modeled by an XML schema, comprising the following steps: using at least one XML data schema describing contents of data to be queried, wherein a collection of data from multiple different databases that are not homogeneous is populated with instances of the at least one XML data schema, wherein the XML data schema is used to generate a query form user interface, wherein the query form user interface comprises an input portion and an output portion; generating query statements in XML Query Language through the use of at least one generator in response to user interaction with the input portion; and invoking from a query assembler to the generator to assemble and submit query requests received at the input portion to the multiple different databases for the execution of the specified query upon the collection of data, wherein a response to the query requests is displayed on the output portion; wherein the input portion of the query form comprises query form controls that are mapped to the XML data schema; wherein a first query form control comprises an instance of a control schema defined by an XML Schema Definition Language file and maps to a specific element of the XML data schema and identifies one or more subquery generators.
10. A computer implemented method to query data modeled by an XML schema, comprising the following steps: using at least one XML data schema describing contents of data to be queried, wherein a collection of data from multiple different databases that are not homogeneous is populated with instances of the at least one XML data schema, wherein the XML data schema is used to generate a query form user interface, wherein the query form user interface comprises an input portion and an output portion; generating query statements in XML Query Language through the use of at least one generator in response to user interaction with the input portion; and invoking from a query assembler to the generator to assemble and submit query requests received at the input portion to the multiple different databases for the execution of the specified query upon the collection of data, wherein a response to the query requests is displayed on the output portion; wherein the input portion of the query form comprises query form controls that are mapped to the XML data schema; wherein a first query form control comprises an instance of a control schema defined by an XML Schema Definition Language file and maps to a specific element of the XML data schema and identifies one or more subquery generators. 13. The method of claim 10 , wherein a run-time engine includes the query assembler and a rendering engine.