title: heterogeneous database query optimization in db2 universal datajoiner. authors: shivakumar venkataraman , tian zhang. venue: vldb. year: 1998
title: implementation of two semantic query optimization techniques in db2 universal database. authors: qi cheng , jarek gryz , fred koo , t. y. cliff leung , linqi liu , xiaoyan qian , k. bernhard schiefer. venue: very large data bases. year: 1999