Answering why-not questions on preference queries

Abstract

After decades of effort working on database performance, the quality and the usability of database systems have received more attention in recent years.Among all the studies that focus on improving databases' usability, the feature of explaining missing tuples in a query result, or the so-called "why-not" questions, has recently become an active topic. When using database system, users may sometimes feel frustrated if they find their expected tuples are not in the query results; and intuitively, they will ask "why are my expected tuples not in the results?" If a database system can give a good explanation for it, it would be very useful for users to understand and refine their queries.In this dissertation, we study the problem of answering why-not questions on preference queries. Our motivation is that we know many users love to pose this kinds of queries when they are making multi-criteria decisions. However, they would also want to know why if their expected answers do not show up in the query results. Therefore, we select three important kinds of preference queries (namely, top-k queries, top-k SQL queries and dominating queries) and develop algorithms to answer such "why-not" questions on each of them.