MRDS provided a command-level interface for defining databases and views (called data submodels), and a call-level interface for queries and data manipulation. A separate Logical Inquiry and Update System (LINUS) provided an online query and update interface. The MRDS query language was similar to SEQUEL (as SQL was first called), with -range, -select, and -where clauses corresponding approximately to the FROM, SELECT, and WHERE clauses of SQL. Explicit set operations (intersection, union, and difference) were provided; there was no direct sorting support. A query was passed as a character string to the MRDS at runtime; there was no precompilation mechanism. Concurrent access to a database by multiple processes was supported; each process was required to explicitly declare the type of access (retrieval or update) and, for update, the scope (set of relations) of the update. The database could be quiesced and backed up in its entirety. A transaction mechanism for atomically committing multiple updates was added in a later release.
As its name implies, MRDS ran on the Multics operating system, and its implementation took advantage of Multics mechanisms for security and virtual memory-based storage. MRDS was written in PL/1.
When MRDS was released in June 1976, it was actually marketed as one of two components of a package called the Multics Data Base Manager (MDBM). The other component was the Multics Integrated Data Store (MIDS), which was a CODASYL database implemented as a layer on top of MRDS.
MRDS was designed by James A. Weeldreyer <Jim.Weeldreyer@iac.honeywell.com> and Oris D. Friesen <email@example.com>; Roger D. Lackey and Richard G. Luebke contributed to the implementation.
Oris D. Friesen and James A. Weeldreyer. "Multics Integrated Data Store: An Implementation of a Network Data Base Manager Utilizing Relational Data Base Methodology. Proceedings of the Eleventh Hawaii International Conference on System Sciences, Volume 1 (January 1978), pages 67-84.
Oris D. Friesen, N.S. Davids, and Rickie E. Brinegar. "MRDS/LINUS: System Evaluation" in J. W. Schmidt and M. L. Brodie, editors. Relational Database Systems: Analysis and Comparison. Berlin, Springer-Verlag (1983), pages 182-220.
Honeywell Information Systems. Series 60 (Level 68). Multics Relational Data Store (MRDS) Reference Manual, Order Number AW53, 1980.
Honeywell Information Systems. Series 60 (Level 68). Logical Inquiry and Update System (Linus) Reference Manual, Order Number AZ49, 1980.
"Honeywell Introduces Multics Data Base Management" Software Digest 8, 35 (September 2, 1976), pages 2-3.
Don Leavitt. "'MDBM' Backs Network, Relational Approaches" ComputerWorld 10?, 35? (September 6, 1976), page 11.
"Honeywell Introduces Data Base Management for Multics 68" Electronic News 21, 1096 (September 6, 1976), page 28.
Tom Van Vleck. Multics web site.