db/journals/dpd/GrefenF96.html Paul W. P. J. Grefen Jan Flokstra Extending a Multi-Set Relational Algebra to a Parallel Environment. 81-99 DPD/4/P081.pdf 1996 4 Distributed and Parallel Databases 1 db/journals/dpd/dpd4.html#GrefenF96 http://kapis.www.wkap.nl/oasis.htm/101566