System R is a database management system which provides a high level relational data interface. The system provides a high level of data independence by isolating the end user as much as possible from underlying storage structures. The system permits definition of a variety of relational views on common underlying data. Data control features are provided, including authorization, integrity assertions, triggered transactions, a logging and recovery subsystem, and facilities for maintaining data consistency in a shared-update environment. This paper contains a description of the overall architecture and design of the system. At the present time the system is being implemented and the design evaluated. We emphasize that System R is a vehicle for research in database architecture, and is not planned as a product.

A multiuser database system must selectively permit users to share data, while retaining the ability to restrict data access. There must be a mechanism to provide protection and security, permitting information to be accessed only by properly authorized users. Further, when tables or restricted views of tables are created and destroyed dynamically, the granting, authentica-tion, and revocation of authorization to use them must also be dynamic. Each of these issues and their solutions in the context of the relational database management system System R are discussed. When a database user creates a table, he is fully and solely authorized to perform upon it actions such as read, insert, update, and delete. He may explicitly grant to any other user any or all of his privileges on the table. In addition he may specify that that user is authorized to further grant these privileges to still other users. The result is a directed graph of granted pri-vileges originating from the table creator. At some later time a user A may revoke some or all of the privileges which he previously granted to another user B. This action usually revokes the entire subgraph of the grants ori-ginating from A’s grant to B. It may be, however, that B will still possess the revoked privi-leges by means of a grant from another user C, and therefore some or all of B’s grants should not be revoked. This problem is discussed in detail, and an algorithm for detecting exactly which of B’s grants should be revoked is presented.

The relational model of data, the XRM Relational Memory System, and the SEQUEL language have been covered in previous papers and are reviewed. SEQUEL is a relational data sublanguage intended for ad hoc interactive problem solving by non-computer specialists. A version of SEQUEL that has been implemented in a prototype interpreter is described. The interpreter is designed to minimize the data accessing operations required to respond to an arbitrary query. The optimization algorithms designed for this purpose are described. Key Words and Phrases: relational model, query language, nonprocedural language, database, data

Throughout the history of information storage in computers, one of the most readily observable trends has been the focus on data independence.