Data access

About: Data access is a research topic. Over the lifetime, 13141 publications have been published within this topic receiving 172859 citations. The topic is also known as: Data access.

Data collection and dissemination system

Abstract: A data collection and dissemination system, in which one or more portable data terminals enter or disseminate data through a wireless access point to which they are communicatively coupled. The wireless access point is also coupled to a portable server for storing and retrieving the information requested by the portable data terminals. The portable server maintains a database for the purposes of storing data from and retrieving data for the portable data terminals. The portable data terminals initiate a transaction with the portable server via communication with the wireless access point. The portable data servers formulate a request to retrieve or store data using a database query. The database query is transmitted to the wireless access point, from which the query is directed to the portable server, which then stores or transmits the requested data. The portable server is connected to other networks and is able to access data on data retrieval devices on these networks, as the data retrieval devices on these networks may also access the data on the portable server. Thus, a wide area network, such as the Internet, provides a backbone network through which the mobile units can communicate to the database server. The mobile units can access data from other mobile units, as other database servers on the networks may also access the data also.

Highly available cluster virtual disk system

Abstract: A cluster implements a virtual disk system that provides each node of the cluster access to each storage device of the cluster. The virtual disk system provides high availability such that a storage device may be accessed and data access requests are reliably completed even in the presence of a failure. To ensure consistent mapping and file permission data among the nodes, data are stored in a highly available cluster database. Because the cluster database provides consistent data to the nodes even in the presence of a failure, each node will have consistent mapping and file permission data. A cluster transport interface is provided that establishes links between the nodes and manages the links. Messages received by the cluster transports interface are conveyed to the destination node via one or more links. The configuration of a cluster may be modified during operation. Prior to modifying the configuration, a reconfiguration procedure suspends data access requests and waits for pending data access requests to complete. The reconfiguration is performed and the mapping is modified to reflect the new configuration. The node then updates the internal representation of the mapping and resumes issuing data access requests.

Ensuring privacy in presence awareness: an automated verification approach

Abstract: Providing information about other users and their activites is a central function of many collaborative applications. The data that provide this "presence awareness" are usually automatically generated and highly dynamic. For example, services such as AOL Instant Messenger allow users to observe the status of one another and to initiate and participate in chat sessions. As such services become more powerful, privacy and security issues regarding access to sensitive user data become critical. Two key software engineering challenges arise in this context:Policies regarding access to data in collaborative applications have subtle complexities, and must be easily modifiable during a collaboration.Users must be able to have a high degree of confidence that the implementations of these policies are correct.In this paper, we propose a framework that uses an automated verification approach to ensure that such systems conform to complex policies. Our approach takes advantage of VeriSoft, a recent tool for systematically testing implementations of concurrent systems, and is applicable to a wide variety of specification and development platforms for collaborative applications. we illustrate the key features of our framework by applying it to the development of a presence awareness system.

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.

Data manipulation in heterogeneous databases

Abstract: Many important information systems applications require access to data stored in multiple heterogeneous databases. This paper examines a problem in interdatabase data manipulation within a heterogeneous environment, where conventional techniques are no longer useful. To solve the problem, a broader definition for join operator is proposed. Also, a method to probabilistically estimate the accuracy of the join is discussed.