16. A hardware computer-readable storage device having computer executable instructions stored therein for improving relevance of search results in response to a user query, said instructions comprising: for receiving a current query from a user; evaluating a set of historical search logs for determining a user satisfaction level for a set of query results returned in response to the current query; iteratively reformulating the current query to construct a new current query, with such iterations repeating until the user satisfaction level exceeds a predetermined threshold, and wherein iteratively reformulating the current query comprises instructions for: evaluating the current query to identify one or more subqueries, each subquery comprised of one or more of the search terms of the current query, evaluating each subquery to select one or more structured data sets from among a plurality of structured data sets from which to retrieve a partial answer corresponding each subquery, for each partial answer retrieved from a selected structured data set, reformulating the current query to construct a new current query by replacing the corresponding subquery with the corresponding partial answer, and retrieving a set of ranked search results corresponding to the new current query; and presenting the set of ranked search results on a display device when the user satisfaction level exceeds the predetermined threshold.
16. A hardware computer-readable storage device having computer executable instructions stored therein for improving relevance of search results in response to a user query, said instructions comprising: for receiving a current query from a user; evaluating a set of historical search logs for determining a user satisfaction level for a set of query results returned in response to the current query; iteratively reformulating the current query to construct a new current query, with such iterations repeating until the user satisfaction level exceeds a predetermined threshold, and wherein iteratively reformulating the current query comprises instructions for: evaluating the current query to identify one or more subqueries, each subquery comprised of one or more of the search terms of the current query, evaluating each subquery to select one or more structured data sets from among a plurality of structured data sets from which to retrieve a partial answer corresponding each subquery, for each partial answer retrieved from a selected structured data set, reformulating the current query to construct a new current query by replacing the corresponding subquery with the corresponding partial answer, and retrieving a set of ranked search results corresponding to the new current query; and presenting the set of ranked search results on a display device when the user satisfaction level exceeds the predetermined threshold. 20. The computer-readable storage device of claim 16 further comprising receiving user feedback to select from two or more possible subqueries when evaluating the current query to identify one or more subqueries.