Research On Key Technologies Of Grid Resource Discovery

Grid is a hot topic in distributed computing nowadays. Just like Web, which is developed to meet the requirement of sharing scientific experimental datum at the beginning, Grid concept is motivated by the needs to share high-performance computer, large database and expensive instrument in modern scientificre research. The real and specific problems that underly the Grid concept are coordinated resource sharing and problem solving in dynamic, multi-institutional virtual organizations. Since 1990s, considerable progress has been made on the construction of such an infrastructure, more over the Grid concept has been widely accepted and refined in many fields such as distributed supercomputing, high-throughput computing and data-intensive computing since then.Resource discovery is a basic element in Grid resource management, which concerns discovering resources in Grid to meet the requirement of applications. Compared with traditional distributed systems, Grid aims to integrate much more resources of diverse varieties belonging to different organizations. In addition, providers and consumers of Grid resources usually have different or even contradictory interests. With further development of Grid, centralized Grid resource discovery schemes give birth to potential scalability problems. Therefore, in order to survive the dynamic and larger-scale Grid environment, resource discovery should be decentralized and should not rely on centralized coordination and control.In addition, with the advancement of the concept of OGSA, resources in Grid are presented to users by the form of services. Therefore, Grid resource discovery show itself as Grid services discovery. The existing keyword-based Grid service discovery methods have some shortages, such as poor flexibility, low precision and low recall. Although the improved methods make some progress in the aspects of flexibility, precision and recall, it still has high time cost on service discovery.Focusing on scalable and efficient decentralized resource discovery in Grid environment, this paper makes following contributions:1. Proposes a novel grid resource discovery method based on adaptive k-Nearest Neighbors clustering, which improves the resource query efficiency and succeed rate.This method uses a two-layer overlay to describe the logical relations between resource nodes. In our method, a class is formed by a collection of nodes with some similarities in their characteristics. Each class is managed by a leader and consists of members that serve as workers. At the same time, to reduce the resource search scope and the propagation scope when updating resource information, we propose a corresponding efficient requests dispatch mechanism. A simulation environment is constructed to study Grid resource discovey performance, and a simulation engine is also implemented. The experimental results show that our method achieves better scalability and efficient lookup performance.2. Proposes a P2P-based Grid resource discovery method with well scalablity.In order to suit the development of the Grid scale and resource dynamics, the P2P method is adopted, and a decentralized resource discovery method with well scalability is presented. This method uses binary tree to manage data, each node in Grid is responsible for managing a part of resource information. It maintains a routing table to guarantee that the search can start at any node as well. At the same time, an algorithm for Grid resource information manangemt is presented, and the message cost of resource information update is also analyzed. For users' resource request, a range query algorithm is proposed and analyzed. The experimental results show that this method resolves many problems that exist in centralized mechanism, such as poor scalability, heavy load on resource information server and single point failure.3. Proposes an ontology-based Grid service discovery method, which improves precison and recall, and reduce the responding time of users' request.To improve the efficiency of Grid service matching, a novel Grid service matching method based on ontology is presented. This method uses OWL-S to describe Grid service, which takes into account the service semantic information. Before matching Grid services, DL-reasoner is used to form concept hierarchy and service hierarchy. The experimental results show that compared with exsiting keyword-based methods and semantic methods, our method has better recall and precision. When compared with the methods based on reasoner directly, although our method has some shortages of time cost for constructing concept hierarchy and service hierarchy, the users' request responding time is notably reduced. Consequently, our method can better meet the needs of users.