Showing papers on "Data access published in 1975"

Random access techniques for data transmission over packet-switched radio channels

Abstract: Terminal access to computer systems has long been and continues to be a problem of major significance. We foresee an increasing demand for access to data processing and storage facilities from interactive terminals, point-of-sales terminals, real-time monitoring terminals, hand-held personal terminals, etc. What is it that distinguishes this problem from other data communication problems? It is simply that these terminals tend to generate demands at a very low duty cycle and are basically bursty sources of data; in addition, these terminals are often geographically distributed. In the computer-to-computer data transmission case, one often sees high utilization of the communication channels; this is just not the case with terminal traffic. Consequently, the cost of providing a dedicated channel to each terminal is often prohibitive. Instead, one seeks ways to merge the traffic from many terminal sources in a way which allows them to share the capacity of one or a few channels, thereby reducing the total cost. This cost savings comes about for two reasons: first, because of the economies of scale present in the communications tariff structure; and secondly, because of the averaging effect of large populations which permit one to provide a channel whose capacity is approximately equal to the sum of the average demands of the population, rather than equal to the sum of the peak demands (i.e., the law of large numbers). This merging of traffic and sharing of capacity has been accomplished in various ways such as: polling techniques, contention systems, multiplexing, concentrating, etc. Many of these are only weak solutions to the problem of gathering low data rate traffic from sources which are geographically dispersed.

An authorization model for a shared data base

Abstract: An authorization model is presented, applicable to a shared data base with well defined data structures. Access to this data base is made through a high level language, which is extended to permit data manipulation and to provide data views for different applications. The authorization model includes: 1) the explicit introduction of the concept of application into the definition of user rights; and 2) the use of predicates that can depend on any data in the system to control access at the data field level. Enforcement of authorization is distributed along time (mostly at compile time), and uses the view mechanism to make evident the application program data requests, which are checked by a centralized procedure that consults the access matrix. The system is shown to provide comprehensive authorization, including implementation of levels and compartments, special access restrictions, content-dependent, context-dependent and functional access.

Secure Data Management System Preliminary Mathematical Model.

Abstract: : In this report a model of a Data Access Monitor (DAM) is developed and certified for operation in an environment in which there are multiple classification levels on subjects and objects. The model is expressed in the program language PASCAL. The MULTICS hierarchical directory structure is modeled and related to the design fundamentals of a relational data management system.

A Conversational Data Access Procedure for CRT Operator Consoles

Abstract: A conversational data access method is proposed in order to avoid the complexity of procedures for data access of CRT operator consoles. The procedure proposed here is composed of three hierarchical steps (tree structural steps), related to the systems of plant components and operational modes. It is concluded from the simulation experiment that the procedure proposed here is superior in many respects to that of the long code entry method.