Donald E. Eastlake III, Matthew Maltzman, Joanne Z. Sattley, Steven A. Zimmerman, "Datacomputer and SIP Operations: Semi-Annual Technical Report", Computer Corporation of America Technical report CCA-79-22, July 31, 1979 at DTIC
ietf.org
Richard Winter, Jeffrey Hill, Warren Greiff, "Further Datalanguage Design Concepts", Network Working Group RFC 610, December 1973, full text