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Security is important for Centralized Data Base Management Systems (CDBMS) and becomes crucial for Distributed Data Base Management Systems (DDBMS) when different organizations share information. Secure cooperation can be achieved only if each participating organization is assured that the data it makes available will not be abused by other users. In this work differences between CDBMS and DDBMS that characterize the nature of the protection problem in DDBMS are identified. These differences are translated into basic protection requirements. Policies that a distributed data base management protection system should allow are described. The system proposed in this work is powerful enough to satisfy the stated requirements and allow for variations on the policies. This system is a hybrid one where both authorizations and constraints can be defined. The system is termed hybrid because it combines features of both open and closed protection systems. In addition the hybrid system, although designed to offer the flexibility of discretionary systems, incorporates the flow control of information between users, a feature found only in some nondiscretionary systems. Furthermore, the proposed system is said to be integrated because authorizations and constraints can be defined on any of the data bases supported by the system including the data bases containing the authorizations, and the constraints themselves. The hybrid system is incorporated in a general model of DDBMS protection. A modular approach is taken for the design of the model. This approach allows us to represent the different options for the model depending on the set of policy choices taken. Three levels of abstraction describing different aspects of DDBMS protection problems are defined. The conceptual level describes the protection control of the DDBMS transactions and information flows. The logical level is concerned with the interaction between the different organizations participating in the DDBMS. The physical level is involved with the architectural implementation of the logical level. / Ph. D.

International Telemetering Conference Proceedings / October 30-November 02, 1995 / Riviera Hotel, Las Vegas, Nevada / Embedded parallel processing provides unique advantages over sequential and symmetrical processing architectures. During the past decade, the architecture of ground control systems has evolved from utilizing sequential embedded processors to modular parallel, distributed, and/or symmetrical processing. The concept of utilizing embedded parallel processing exhibits key features such as modularity, flexibility, scalability, host independence, non-contention of host resources, and no requirement for an operating system. These key features provide the performance, reliability and efficiency while at the same time lowering costs. Proper utilization of embedded parallel processing on a host computer can provide fault tolerance and can greatly reduce the costs and the requirement of utilizing high-end workstations to perform the same level of real-time processing and computationally intensive tasks.

A research report submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in partial fulfilment of the requirements for the degree of Master of Science / This research report investigates the application of Charron-Bost's measure of currency m to Milner's Calculus of Communicating Systems (CCS). The aim of this is twofold: first to evaluate the measure m in terms of criteria gathered from the literature: and second to determine the feasiblllty of measuring concurrency in CCS and hence provide a new tool for understanding concurrency using CCS. The approach taken is to identify the differences hetween the message-passing formalism in which the measure m is defined, and CCS and to modify this formalism to-enable the mapping of CCS agents to it. A software tool, the Concurrency Measurement Tool, is developed to permit experimentation with chosen CCS agents. These experiments show that the measure m, although intuitively appealing, is defined by an algebraic expression that is ill-behaved. A new measure is defined and it is shown that it matches the evaluation criteria better than m, although it is still not ideal. This work demonstrates that it is feasible to measure concurrency in CCS and that a methodology has been developed for evaluating concurrency measures. / Andrew Chakane 2018

University of Macau / Faculty of Science and Technology. / Department of Computer and Information Science