Browsing by Author "Cetintemel, Ugur"
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Item Flexible User Profiles for Large Scale Data Delivery(1999-03-30) Cetintemel, Ugur; Franklin, Michael J.; Giles, C. LeePush-based data delivery requires knowledge of user interests for making scheduling, bandwidth allocation, and routing decisions. Such information is maintained as user profiles. We propose a new incremental algorithm for constructing user profiles based on monitoring and user feedback. In contrast to earlier approaches, which typically represent profiles as a single weighted interest vector, we represent user-profiles using multiple interest clusters, whose number, size, and elements change adaptively based on user access behavior. This flexible approach allows the profile to more accurately represent complex user interests. The approach can be tuned to trade off profile complexity and effectiveness, making it suitable for use in large-scale information filtering applications such as push-based WWW page dissemination. We evaluate the method by experimentally investigating its ability to categorize WWW pages taken from Yahoo! categories. Our results show that the method can provide high retrieval effectiveness with modest profile sizes and can effectively adapt to changes in users' interests. Also cross-referenced as UMIACS-TR-99-18Item Partitioning vs. Replication for Token-Based Commodity(2000-09-12) Cetintemel, Ugur; Ozden, Banu; Franklin, Michael J.; Silberschatz, AviThe proliferation of e-commerce has enabled a new set of applications that allow globally distributed purchasing of commodities such as books, CDs, travel tickets, etc., over the Internet. These commodities can be represented on line by tokens, which can be distributed among servers to enhance the performance and availability of such applications. There are two main approaches for distributing such tokens ? replication and partitioning. Token replication requires expensive distributed synchronization protocols to provide data consistency, and is subject to both high latency and blocking in case of network partitions. On the other hand, token partitioning allows many transactions to execute locally without any global synchronization, which results in low latency and immunity against network partitions. In this paper, we examine the Data-Value Partitioning (DVP) approach to token-based commodity distribution. We propose novel DVP strategies that vary in the way they redistribute tokens among the servers of the system. Using a detailed simulation model and real Internet message traces, we investigate the performance of our DVP strategies by comparing them against a previously proposed scheme, Generalized Site Escrow (GSE), which is based on replication and escrow transactions. Our experiments demonstrate that, for the types of applications and environment we address, replication-based approaches are neither necessary nor desirable, as they inherently require quorum synchronization to maintain consistency. We show that DVP, primarily due to its ability to provide high server autonomy, performs favorably in all cases studied. (Also cross-referenced as UMIACS-TR-2000-62Item A Security Infrastructure for Mobile Transactional Systems(2000-07-11) Keleher, Peter J.; Bhattacharjee, Bobby; Kuo, Kuo-Tung; Cetintemel, UgurIn this paper, we present an infrastructure for providing secure transactional support for mobile databases. Our infrastructure protects against external threats - malicious actions by nodes not authorized to access the data. The major contribution of this paper, however, is to classify and present algorithms to protect against internal security threats. Internal threats are malicious ac-tions by authenticated nodes that misrepresent protocol specific information. We quantify the cost of our security mechanisms in context of Deno: a system that supports object replication in a transactional framework for mobile and weakly-connected environments. Our results show that protecting against internal threats comes at a cost, but the marginal cost for protecting against larger cliques of malicious insiders is low. However, even with all the security mechanisms in place, our system commits updates over 50% faster than systems that depend on the Read-once Write-all commit protocol. Lastly, we present results from a probabilistic version of our algorithm that has several orders of magnitude lower computation cost than the traditional public-key based schemes. (Also cross-referenced as UMIACS-TR-2000-19)Item A Security Infrastructure for Mobile Transactional Systems(2000-08-16) Cetintemel, Ugur; Keleher, Peter J.; Bhattacharjee, BobbyIn this paper, we present an infrastructure for providing secure transactional replication support for peer-to-peer, decentralized databases. We first describe how to effectively provide protection against external threats, malicious actions by servers not authorized to access data, using conventional cryp-tography-based mechanisms. We then classify and present algorithms that provide protection against internal threats, malicious actions by authenticated servers that misrepresent protocol-specific infor-mation. Our approach to handling internal threats uses both cryptographic techniques and modifica-tions to the update commit criteria. The techniques we propose are unique in that they not only enable a tradeoff between performance and the degree of tolerance to malicious servers, but also allow for indi-vidual servers to support non-uniform degrees of tolerance without adversely affecting the performance of the rest of the system. We investigate the cost of our security mechanisms in the context of Deno: a prototype object replica-tion system designed for use in mobile and weakly-connected environments. Experimental results reveal that protecting against internal threats comes at a cost, but the marginal cost for protecting against larger cliques of malicious insiders is generally low. Furthermore, comparison with a decentralized Read-One Write-All protocol shows that our approach performs significantly better under various workloads. (Also cross-referenced as UMIACS-TR-2000-59)Item Support for Speculative Update Propagation and Mobility in Deno(2000-07-11) Cetintemel, Ugur; Keleher, Peter J.; Franklin, MichaelThis paper presents the transactional framework of Deno, an object replication system specifically designed for use in mobile and weakly-connected environments. Deno uses weighted voting for availability and pair-wise, epidemic information flow for flexibility. This combination allows the protocols to operate with less than full connectivity, to easily adapt to changes in group member-ship, and to make few assumptions about the underlying network topology. These features are all crucial to providing effective support for mobile and weakly-connected platforms. Deno has been implemented and runs on top of Linux and Windows NT/CE platforms. We use the Deno prototype to characterize the performance of two versions of Deno's protocol. The first ver-sion enables globally serializable execution of update transactions. The second supports a weaker consistency level that still guarantees transactionally consistent access to replicated data. The re-sults show that our protocols either outperform or perform comparably to existing approaches, while achieving higher availability. Further, we show that the incremental cost of providing global serializability in this environment is low. Finally, we show that commit delays can be sig-nificantly decreased by allowing votes to be cast, and votes and updates to be disseminated, speculatively. (Also cross-referenced as UMIACS-TR-99-70)