Abstract: In the recent years, the quality and the usability of database systems have received more attention. The performance of database systems has gained more improvement in the past decades so, they are more and more difficult to use. The why-not questions are needs of user to know why her expected tuples are not shown up in the query results i.e. the features of explaining missing tuples in database queries. Database system is having the capability that enables users to seek clarifications on expected query results as well as the absence of expected tuples (i.e. missing tuples). It would be very helpful to users if they referred why-not questions to seek clarifications on expected tuples in query results. There are two algorithms to answer why-not questions efficiently. These algorithms are able to return high quality explanations efficiently. Many users love to pose those kinds of queries when they are making multi-criteria decisions and user need approximate information from the huge Database.

Keywords: Top-k Question, Dominating Question, Skyline Refined Queries, ConQueR Method.