title: sideway value algebra for object-relational databases. authors: g жzsoyoglu , a al-hamdani , i altingіvde , s жzel , ж ulusoy , z жzsoyoglu. venue: vldb. year: 2002
title: extended algebra and calculus for nested relational databases. authors: ma roth , hf korth , a silberschatz. venue: acm transactions on database systems ,. year: 1988.0