The paper concerns a new type of system, called a multidatabase management system, designed to manage multiple databases. This system doesn’t assume the existence of a global schema, in general, but an interoperability of particular databases is required.

The authors present a prototype multidatabase system, called Multics Relational Data Store Multidatabase (MRDSM). The cooperating databases are manipulable through the relational DBMS MRDS. The manipulation language MDSL makes it possible to join data in different database schemas, to evaluate interdatabase queries, to create dynamic aggregation of data from different databases, as well as to exchange data between databases. Statements of MDSL are able to be processed despite eventual semantic conflicts between the participating schemas.

The paper is structured into two sections. The first talks about data description level and deals with problems of database schemas, database access and identification, multidatabase naming, and interdatabase dependencies.

The second section discusses MDSL based on the tuple calculus. The language is presented using plenty of examples. New ideas are given on the processing of multiple queries, which are intended for situations where various databases model the same universe. The formulation of most relational queries is simplified by implicit joins. Dynamic attributes make it possible for the user to dynamically and subjectively transform data values.

The paper is well organized and easy to read. The features and new concepts designed for the described system are not only useful in a multiple database environment, but should be worthwhile in any relational DBMS.