db/journals/dpd/GrefenW97.html Paul W. P. J. Grefen Jennifer Widom Protocols for Integrity Constraint Checking in Federated Databases. 327-355 DPD/5/P327.pdf 1997 5 Distributed and Parallel Databases 4 db/journals/dpd/dpd5.html#GrefenW97 http://kapis.www.wkap.nl/oasis.htm/140024