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.

Bridging the gap: a virtual health record for integrated home care

Abstract: Introduction : The coexistence of different information systems that are unable to communicate is a persistent problem in healthcare and in integrated home care in particular. Theory and methods : Physically federated integration is used for design of the underlying technical architecture to implement a mobile virtual health record for integrated home care. A user centered system development approach is followed during design and development of the system. Results : A technical platform based on a service-oriented approach where database functionality and services are separated has been developed. This guarantees flexibility with regard to changed functional demands and allows third party systems to interact with the platform in a standardized way. A physically federated integration enables point-of-care documentation, integrated presentation of information from different feeder systems, and offline access to data on handheld devices. Feeder systems deliver information in XML-files that are mapped against an ideal XML schema, published as an interface for integration with the information broker, and inserted into the mediator database. Conclusions : A seamless flow of information between both different care professionals involved in integrated home care and patients and relatives is provided through mobile information access and interaction with different feeder systems using the virtual health record.

Multilevel secure database concurrency control

Abstract: The implications of multilevel security on database concurrency control are explored. Transactions are vital for multilevel secure database management systems (MLS/DBMSs) because they provide transparency to concurrency and to failure. Concurrent execution of transactions may lead to contention among subjects for access to data, which in MLS/DBMSs may lead to security problems. An abstraction of security models in terms of the transactions which they produce is presented. The notion of DC-Security which identifies a class of covert channels that are caused by contention for access to shared data, is introduced. This notion is useful for evaluating the security of transaction schedulers. A framework for multilevel secure schedulers which allows analysis of a schedulers' security properties at the protocol level is presented. Necessary and sufficient conditions are developed for DC-Security in this framework and proved using noninterference. A wide range of schedulers is evaluated against these conditions. >

DP²AC: Distributed Privacy-Preserving Access Control in Sensor Networks

Abstract: The owner and users of a sensor network may be different, which necessitates privacy-preserving access control. On the one hand, the network owner need enforce strict access control so that the sensed data are only accessible to users willing to pay. On the other hand, users wish to protect their respective data access patterns whose disclosure may be used against their interests. This paper presents DP 2 AC, a Distributed Privacy- Preserving Access Control scheme for sensor networks, which is the first work of its kind. Users in DP 2 AC purchase tokens from the network owner whereby to query data from sensor nodes which will reply only after validating the tokens. The use of blind signatures in token generation ensures that tokens are publicly verifiable yet unlinkable to user identities, so privacy- preserving access control is achieved. A central component in DP 2 AC is to prevent malicious users from reusing tokens. We propose a suite of distributed techniques for token-reuse detection (TRD) and thoroughly compare their performance with regard to TRD capability, communication overhead, storage overhead, and attack resilience. The efficacy and efficiency of DP 2 AC are confirmed by detailed performance evaluations.

The PH-tree: a space-efficient storage structure and multi-dimensional index

Abstract: We propose the PATRICIA-hypercube-tree, or PH-tree, a multi-dimensional data storage and indexing structure. It is based on binary PATRICIA-tries combined with hypercubes for efficient data access. Space efficiency is achieved by combining prefix sharing with a space optimised implementation. This leads to storage space requirements that are comparable or below storage of the same data in non-index structures such as arrays of objects. The storage structure also serves as a multi-dimensional index on all dimensions of the stored data. This enables efficient access to stored data via point and range queries. We explain the concept of the PH-tree and demonstrate the performance of a sample implementation on various datasets and compare it to other spatial indices such as the kD-tree. The experiments show that for larger datasets beyond 10^7 entries, the PH-tree increasingly and consistently outperforms other structures in terms of space efficiency, query performance and update performance.

The Small World of File Sharing

Abstract: Web caches, content distribution networks, peer-to-peer file-sharing networks, distributed file systems, and data grids all have in common that they involve a community of users who use shared data. In each case, overall system performance can be improved significantly by first identifying and then exploiting the structure of community's data access patterns. We propose a novel perspective for analyzing data access workloads that considers the implicit relationships that form among users based on the data they access. We propose a new structure-the interest-sharing graph-that captures common user interests in data and justify its utility with studies on four data-sharing systems: a high-energy physics collaboration, the Web, the Kazaa peer-to-peer network, and a BitTorrent file-sharing community. We find small-world patterns in the interest-sharing graphs of all four communities. We investigate analytically and experimentally some of the potential causes that lead to this pattern and conclude that user preferences play a major role. The significance of small-world patterns is twofold: it provides a rigorous support to intuition and it suggests the potential to exploit these naturally emerging patterns. As a proof of concept, we design and evaluate an information dissemination system that exploits the small-world interest-sharing graphs by building an interest-aware network overlay. We show that this approach leads to improved information dissemination performance.