An authorization mechanism for a relational data base system

A multi-user data base system must permit users to selectively 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, authentication, and revocation of authorization to use them must also be dynamic. We discuss each of these issues and their solutions in the context of the relational data base management system, System R.When a data base user creates a table, he is fully and solely authorized to perform actions upon it such as read, insert, update, and delete. If he wishes, 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 other users. The result is a directed graph of granted privileges 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 originating from A's grant to B. It may be, however, that B will still possess the revoked privileges by means of a grant from another user C, and therefore some or all of B's grants should not be revoked. We discuss this problem in detail and present an algorithm for detecting exactly which of B'S grants should be revoked.Because revocation may be performed dynamically, a user's authorization for a table must be checked dynamically. We present a scheme which attempts to minimize the cost of such revalidation.