Foundations and Trends in Information Retrieval
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The Web and Web-based open systems are characterized by their massive amount of data and services for leveraging this data. These systems are noted for their open and unregulated nature, self-supervision, and high degree of dynamism, which are key features in supporting a rich set of opportunities for information sharing, discovery, and commerce. But these open and self-managing features also carry risks and raise growing concerns over the security and privacy of these systems, including issues like spam, denial-of-service, and impersonated digital identities. Our focus in this thesis is on the design, implementation, and analysis of large-scale Web-based open systems, with an eye toward enabling new avenues of information discovery and ensuring robustness in the presence of malicious participants. We identify three classes of vulnerabilities that threaten these systems: vulnerabilities in link-based search services, vulnerabilities in reputation-based trust services over online communities, and vulnerabilities in Web categorization and integration services. This thesis introduces a suite of methods for increasing the tamper-resilience of Web-based open systems in the face of a large and growing number of threats. We make three unique contributions: First, we present a source-centric architecture and a set of techniques for providing tamper-resilient link analysis of the World Wide Web. We propose the concept of link credibility and present a credibility-based link analysis model. We show that these approaches significantly reduce the impact of malicious spammers on Web rankings. Second, we develop a social network trust aggregation framework for supporting tamperresilient trust establishment in online social networks. These community-based social networking systems are already extremely important and growing rapidly. We show that our trust framework supports high quality information discovery and is robust to the presence of malicious participants in the social network. Finally, we introduce a set of techniques for reducing the opportunities of attackers to corrupt Web-based categorization and integration services, which are especially important for organizing and making accessible the large body of Web-enabled databases on the Deep Web that are beyond the reach of traditional Web search engines. We show that these techniques reduce the impact of poor quality or intentionally misleading resources and support personalized Web resource discovery.