Grid computing is a virtualized distributed computing environment aimed at enabling the sharing of
geographically distributed resources. Grid resources have traditionally consisted of dedicated supercomputers, clusters, or storage units. With the present ubiquitous network connections and the growing computational and storage capabilities of modem everyday-use computers, more resources such as PCs, devices (e.g., PDAs and sensors), applications, and services are on grid networks. Grid is expected to
evolve from a computing and data management facility to a pervasive, world-wide resource-sharing
infrastructure. To fully utilize the wide range of grid resources, effective resource discovery mechanisms
are required. However, resource discovery in a global-scale grid is challenging due to the considerable
diversity, large number, dynamic behavior, and geographical distribution of the resources. The resource
discovery technology required to achieve the ambitious global grid vision is still in its infancy, and
existing applications have difficulties in achieving both rich searchability and good scalability. In this
thesis, we investigate the resource discovery problem for open-networked global-scale grids. In
particular, we propose a distributed semantics-based discovery framework. We show how this framework
can be used to address the discovery problem in such grids and improve three aspects of performance:
expressiveness, scalability, and efficiency.
Expressiveness is the first characteristic that a grid resource-searching mechanism should have. Most
existing search systems use simple keyword-based lookups, which limit the searchability of the system.
Our framework improves search expressiveness from two directions: First, it uses a semantic metadata
scheme to provide users with a rich and flexible representation mechanism, to enable effective
descriptions of desired resource properties and query requirements. Second, we employ ontological
domain knowledge to assist in the search process. The system is thus able to understand the semantics of
query requests according to their meanings in a specific domain; this procedure helps the system to locate
only semantically related results.
The more expressive the resource description and query request, however, the more difficult it is to
design a scalable and efficient search mechanism. We ensure scalability by reconfiguring the network
with respect to shared ontologies. This reconfiguration partitions the large unorganized search space into
multiple well-organized semantically related sub-spaces that we call semantic virtual organizations.
Semantic virtual organizations help to discriminatively distribute resource information and queries to
related nodes, thus reducing the search space and improving scalability. To further improve the
efficiency of searching the virtual organizations, we propose two semantics-based resource-integrating
and searching systems: GONID and OntoSum. These two systems address searching problems for
applications based on different network topologies: structured and unstructured peer-to-peer overlay
networks. Queries in the search systems are processed in a transparent way, so that users accessing the
data can be insulated from the fact that the information is distributed across different sources and represented with different formats. In both systems, ontological knowledge is decomposed into different
coarse-grained elements, and then these elements are indexed with different schemes to fit the
requirements of different applications. Resource metadata reasoning, integrating, and searching are based
on the index. A complex query can be evaluated by performing relational operations such as select,
project, and join on combinations of the indexing elements.
We evaluate the performance of our system with extensive simulation experiments, the results of which
confirm the effectiveness of the design. In addition, we implement a prototype that incorporates our
ontology-based virtual organization formation and semantics-based query mechanisms. Our deployment
of the prototype verifies the system's feasibility and its applicability to real-world applications.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:BVAU./2845 |
| Date | 11 1900 |
| Creators | Li, Juan |
| Publisher | University of British Columbia |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Format | 19992969 bytes, application/pdf |
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