1. A computer based system for querying a markup language document having hierarchical information including a parent node and descendent nodes related to the parent node, comprising: a data source having stored therein a markup language document; and a wrapper unit configured to retrieve the markup language document, identify and extract information from the retrieved markup language document in response to a query by consulting a mapping specification containing information for locating the parent node, and if the parent node satisfies the query to store the parent node in a first table, and to locate the descendent nodes by consulting the mapping specification if the parent node satisfies the query and store said descendent nodes in a second table.