1. An apparatus comprising: a computer processor; a memory coupled to the processor; an XML data storage schema portion for obtaining XML data as input; a workload schema portion for obtaining workload input, wherein the workload schema portion includes data comprising XML queries and XML query transformations; a semi-structured data storage schema for mapping the workload schema portion into a relational schema; a set of semi-structured data storage schema candidates are automatically generated; an XML storage schema selection portion for automatically selecting an improved XML data storage schema for the relational schema in response to the XML data and in response to the workload input, wherein the XML data storage schema selection portion segments the XML data based on the selected improved XML data storage schema, the semi-structured data storage schema for tracking and evaluating the XML data after a duration; and a cost model for calculating a cost for an initial state, wherein the cost model includes parameters consisting of an instance number of an element, a field width of the element, an average fan out from one element to another element, a number of elements in an extend of a field, a size of the extend of a fragment, a selectivity of a simple path, and the selectivity of a path from a root to the fragment.