4. The method of claim 1 , wherein the query is split into a first part q1 and a second part q2 and the quality estimation function depends on a first probability p1 and a second probability p2, wherein 
 p 1 =p ( q 2 |q 1), and 
 p 2 =p ( q 1 |q 2).
4. The method of claim 1 , wherein the query is split into a first part q1 and a second part q2 and the quality estimation function depends on a first probability p1 and a second probability p2, wherein 
 p 1 =p ( q 2 |q 1), and 
 p 2 =p ( q 1 |q 2). 7. The method of claim 4 , wherein the first part q1 corresponds substantially to the first half of the query and the second part q2 corresponds substantially to the second half of the query.