http://doi.acm.org/10.1145/984382.984393 db/journals/sigmod/GerritsenMZ77.html Rob Gerritsen Howard L. Morgan Michael Zisman On Some Metrics for Databases or What is a Very Large Database? 50-74 sigmodR/09-1/P050.pdf 1977 9 SIGMOD Record 1 db/journals/sigmod/sigmod9.html#GerritsenMZ77