title: xxl - a library approach to supporting efficient implementations of advanced database queries. authors: björn blohsfeld , jens-peter dittrich , martin schneider , bernhard seeger , tobias schäfer , jochen van den bercken , jürgen krämer. venue: vldb. year: 2001
title: join index hierarchies for supporting efficient navigations in object-oriented databases. authors: zhaohui xie , jiawei han. venue: very large data bases. year: 1994