title: a robust , optimization-based approach for approximate answering of aggregate queries. authors: vivek r. narasayya , gautam das , surajit chaudhuri. venue: sigmod conference. year: 2001
title: answering queries with aggregation using views. authors: divesh srivastava , shaul dar , h. v. jagadish , alon y. levy. venue: very large data bases. year: 1996