“A History and Evaluation of System R”(PDF). IBM. "Phase Zero" of the project, which occurred during 1974 and-most of 1975, involved the development of the SQL user interface
Selinger, PG; Astrahan, MM; Chamberlin, Donald D; Lorie, RA; Price, TG (1979), 〈Access Path Selection in a Relational Database Management System〉,《Proceedings of the 1979 ACM SIGMOD International Conference on Management of Data》, 23–34쪽, doi:10.1145/582095.582099
