5. The method of claim 4 , wherein, before determining p1, the folding-in technique of PLSI is used to estimate the PLSI decomposition model p(aspect|q1) which is then used to determine p1.
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).