In this paper, we present a scalable Peer-to-Peer RDF repository, named RDF-Peers, which stores each triple in a multi-attribute addressable network by applying globally known hash functions. Queries can be efficiently routed to the nodes that store matching triples. RDFPeers also supports users to selectively subscribe to RDF content. In RDFPeers, both the neighbors per node and the routing hops for triple insertion, most query resolution and triple subscription are logarithmic to the network size. Our experiments with real-world RDF data demonstrated that the triple-storing load among nodes in RDFPeers differs by less than an order of magnitude.

Data Grids are an emerging new technology for managing large amounts of distributed data. This technology is highly-anticipated by scientific communities, such as in the area of astronomy, protein simulation and high energy physics. This is because experiments in these fields generate massive amount of data which need to be shared and analysed. Since it is not possible to test many different usage scenarios on real Data Grid testbeds, it is easier to use simulation as a means of studying complex scenarios.

Peer-to-peer networks based on Distributed Hash Tables (DHTs) have received considerable attention ever since their introduction in 2001. Unfortunately, DHT-based systems have shown to be notoriously difficult to protect against security attacks. Various reports have been published that discuss or classify general security issues, but so far a comprehensive survey describing the various proposed defenses has been lacking. In this paper, we present an overview of techniques reported in the literature for making DHT-based systems resistant to the three most important attacks that can be launched by malicious nodes participating in the DHT: (1) the Sybil attack, (2) the Eclipse attack, and (3) routing and storage attacks. We review the advantages and disadvantages of the proposed solutions and in doing so, confirm how difficult it is to secure DHT-based systems in an adversarial environment.

We study Grid architectures and relate them to the ideas of collaboration and community networks. We discuss services and architectural principles that support both synchronous and asynchronous collaboration and the integration with community networks and peer-to-peer systems. We identify 18 core features and services that characterize Grid systems. We conclude with a proposed Semantic Scholars ’ Grid integrating these concepts to support information discovery and sharing in communities of users.

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With a growing trend towards grid-based data repositories and data analysis services, scientific data analysis often involves accessing multiple data sources, and analyzing the data using a variety of analysis programs. One critical challenge in this, however, is that data sources often hold the same type of data in a number of different formats, and also, the formats expected and generated by various data analysis services are often distinct. We believe that the traditional approach for dealing with this problem, which is using hand-written wrappers, is not an effective and scalable solution for a grid environment. This paper presents a new approach, which involves generating wrappers automatically for enabling grid-based information integration and workflows. In this approach, a layout descriptor is used for describing the data format for each data source, as well as the input and output format for each tool or service. Efficient wrappers are then generated automatically for translation between any two data formats. Our design separates wrapper generation service from the wrapper execution. The wrapper generation service analyzes the layout descriptors and generates a WRAPINFO data structure. The wrapper comprises a set of application independent modules which take the WRAP-INFO data structure as the input. We demonstrate our wrapper generation tool with two real case studies. Besides showing the effectiveness of our system, the experiments results from these two case studies show that the wrapper generation overhead is very small, automatically generated wrappers scale well to large datasets, and for the one case where this comparison was possible, the execution time of our wrapper was within 30 % of that of a hand-written one. 1.

Traditional peer-to-peer (p2p) applications such as Kazaa and Gnutella have been primarily used for sharing read-only files (such as mpegs, jpegs, and mp3s) over the Internet. Such applications did not demand mechanisms to protect concurrent access and update to shared data, and therefore mutual exclusion has not yet been thoroughly studied in the p2p community. Due to the recent surge in the area of Grid computing, there is an urgency to find efficient ways of sharing resources. In the future, application developers should be able to write Grid and p2p applications without worrying about handling the low-level details of protecting consistent and concurrent access to shared resources. This thesis proposes two novel protocols for achieving mutual exclusion efficiently in dynamic p2p systems. The protocols are layered atop a distributed hash table (DHT), making them scalable and fault-tolerant. The burden of controlling access to the critical section is also evenly distributed among all the nodes in the network, making the protocols more distributed and easily adaptable to growing networks. Since the protocols are designed independent of any specific DHT implementation, they can be incorporated

Distributed computing systems employ replication to improve overall system robustness, scalability and performance. A Replica Location Service (RLS) offers a mechanism to maintain and provide information about physical locations of replicas. This paper defines a design framework for replica location services that supports a variety of deployment options. We describe the RLS implementation that is distributed with the Globus Toolkit and is in production use in several Grid deployments. Features of our modular implementation include the use of soft-state protocols to populate a distributed index and Bloom filter compression to reduce overheads for distribution of index information. Our performance evaluation demonstrates that the RLS implementation scales well for individual servers with millions of entries and up to one hundred clients. We describe the characteristics of existing RLS deployments and discuss how RLS has been integrated with higher-level data management services.

This paper describes an architecture for an archival data storage. The design enables aggregation of storage resources in scalable fashion to achieve a highly reliable data storage. Reliability is implemented by using erasure coding which provides the less storage overhead than full replication. Scalability of the architecture is achieved through the ability to work with multiple different storage locations and a scalable metadata management system. The integrity of the data is ensured through use of cryptographic naming. Feasibility of the proposed design is assessed with a real world implementation named GB-DISK. 1

The exploration in many scientific disciplines (e.g., High-Energy Physics, Climate Modeling, and Life Sciences) involves the production and the analysis of massive data collections, whose archival, retrieval, and analysis require the coordinated usage of high capacity computing, network, and storage resources. To obtain satisfactory performance, these applications require the availability of a high-performance, reliable data transfer mechanisms, able to minimize the data transfer time that often dominates their execution time. In this paper we present the File Mover, an efficient data transfer system specifically tailored to the needs of data-intensive applications, that exploits the overlay networks paradigm to provide superior performance with respect to conventional file transfer systems. An extensive experimental evaluation, carried out by means of a proof-of-concept implementation of the File Mover for a variety of network scenarions, shows the ability of the File Mover to outperform alternative data transfer systems. 1