1. A computer-based method for context-sensitive decomposition of a markup based document into a relational database, based on schemas with reusable item declarations, comprising: (a) creating a mapping document from a schema of a markup based document with at least one reusable item declaration defining an item being mapped to different tables/columns pairs, depending on the item's ancestry; (b) annotating the mapping document with the item ancestry mapping annotation having a location path of the item; and (c) decomposing each said item into a corresponding database table column.