Browsing by Subject "Experimentation"
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Item Open Access Automatic ranking of information retrieval systems using data fusion(Elsevier Ltd, 2006-05) Nuray, R.; Can, F.Measuring effectiveness of information retrieval (IR) systems is essential for research and development and for monitoring search quality in dynamic environments. In this study, we employ new methods for automatic ranking of retrieval systems. In these methods, we merge the retrieval results of multiple systems using various data fusion algorithms, use the top-ranked documents in the merged result as the "(pseudo) relevant documents," and employ these documents to evaluate and rank the systems. Experiments using Text REtrieval Conference (TREC) data provide statistically significant strong correlations with human-based assessments of the same systems. We hypothesize that the selection of systems that would return documents different from the majority could eliminate the ordinary systems from data fusion and provide better discrimination among the documents and systems. This could improve the effectiveness of automatic ranking. Based on this intuition, we introduce a new method for the selection of systems to be used for data fusion. For this purpose, we use the bias concept that measures the deviation of a system from the norm or majority and employ the systems with higher bias in the data fusion process. This approach provides even higher correlations with the human-based results. We demonstrate that our approach outperforms the previously proposed automatic ranking methods. © 2005 Elsevier Ltd. All rights reserved.Item Open Access Cache-based query processing for search engines(Association for Computing Machinery, 2012-11-01) Cambazoglu, B. B.; Altıngovde, I. S.; Ozcan, R.; Ulusoy, ÖzgürIn practice, a search engine may fail to serve a query due to various reasons such as hardware/network failures, excessive query load, lack of matching documents, or service contract limitations (e.g., the query rate limits for third-party users of a search service). In this kind of scenarios, where the backend search system is unable to generate answers to queries, approximate answers can be generated by exploiting the previously computed query results available in the result cache of the search engine.In this work, we propose two alternative strategies to implement this cache-based query processing idea. The first strategy aggregates the results of similar queries that are previously cached in order to create synthetic results for new queries. The second strategy forms an inverted index over the textual information (i.e., query terms and result snippets) present in the result cache and uses this index to answer new queries. Both approaches achieve reasonable result qualities compared to processing queries with an inverted index built on the collection. © 2012 ACM.Item Open Access Compiler directed network-on-chip reliability enhancement for chip multiprocessors(Association for Computing Machinery, 2010-04) Ozturk, O.; Kandemir, M.; Irwin, M. J.; Narayanan, S.H. K.Chip multiprocessors (CMPs) are expected to be the building blocks for future computer systems. While architecting these emerging CMPs is a challenging problem on its own, programming them is even more challenging. As the number of cores accommodated in chip multiprocessors increases, network-on-chip (NoC) type communication fabrics are expected to replace traditional point-to-point buses. Most of the prior software related work so far targeting CMPs focus on performance and power aspects. However, as technology scales, components of a CMP are being increasingly exposed to both transient and permanent hardware failures. This paper presents and evaluates a compiler-directed power-performance aware reliability enhancement scheme for network-on-chip (NoC) based chip multiprocessors (CMPs). The proposed scheme improves on-chip communication reliability by duplicating messages traveling across CMP nodes such that, for each original message, its duplicate uses a different set of communication links as much as possible (to satisfy performance constraint). In addition, our approach tries to reuse communication links across the different phases of the program to maximize link shutdown opportunities for the NoC (to satisfy power constraint). Our results show that the proposed approach is very effective in improving on-chip network reliability, without causing excessive power or performance degradation. In our experiments, we also evaluate the performance oriented and energy oriented versions of our compiler-directed reliability enhancement scheme, and compare it to two pure hardware based fault tolerant routing schemes. © 2010 ACM.Item Open Access Evolution of web search results within years(ACM, 2011-07) Altıngövde, İsmail Şengör; Özcan, Rıfat; Ulusoy, ÖzgürWe provide a first large-scale analysis of the evolution of query results obtained from a real search engine at two distant points in time, namely, in 2007 and 2010, for a set of 630,000 real queries.Item Open Access A model of boundedly rational learning in dynamic games(Bilkent University, 1997) Aksoy, HakanThere are various computer-based algorithms about boundedly rational players’ learning how to behave in dynamic games, including classifier systems, genetic algorithms and neural networks. Some examples of studies using boundedly rational players are Axelrod (1987), Miller (1989), Andreoni and Miller (1990) who use genetic algorithm and Marimon etal. (1990) and Arthur (1990) who use classifier systems. In this dissertation, a Two Armed Bandit Problem and the KiyotakiWright (1989) Economic Environment are constructed and the learning behaviour ol the boundedly rational players is observed by using classifier systems in computer programs. From the simulation results, we observe that experimentation and imitation enables faster convergence to the correct decision rules of players in both repeated static decision problems and dynamic games.Item Open Access My imaginary world: an analysis of styles in polish animation in terms of invention and experimentation(Bilkent University, 2016-05) Brzozowska, MariaThis thesis accompanies my short animation My Imaginary World. The paper explores experimentation with animation. The thesis looks at experimental animation; it’s meaning and explores whether there is a specific way of carrying out an experiment with animation. It presents various experimental artist from the Polish school of animation, analyzes their working methods and describes how they have influenced the outcome of this project. Lastly a detailed description of the visual project, its functions and displayed are detailed. Creating an animation for the first time, this thesis has helped me take the next step in my artistic journey, presenting a broader understanding of the new technology that I have at hand as an artist.Item Open Access Optimizing shared cache behavior of chip multiprocessors(ACM, 2009-12) Kandemir, M.; Muralidhara, S. P.; Narayanan, S. H. K.; Zhang, Y.; Öztürk, ÖzcanOne of the critical problems associated with emerging chip multiprocessors (CMPs) is the management of on-chip shared cache space. Unfortunately, single processor centric data locality optimization schemes may not work well in the CMP case as data accesses from multiple cores can create conflicts in the shared cache space. The main contribution of this paper is a compiler directed code restructuring scheme for enhancing locality of shared data in CMPs. The proposed scheme targets the last level shared cache that exist in many commercial CMPs and has two components, namely, allocation, which determines the set of loop iterations assigned to each core, and scheduling, which determines the order in which the iterations assigned to a core are executed. Our scheme restructures the application code such that the different cores operate on shared data blocks at the same time, to the extent allowed by data dependencies. This helps to reduce reuse distances for the shared data and improves on-chip cache performance. We evaluated our approach using the Splash-2 and Parsec applications through both simulations and experiments on two commercial multi-core machines. Our experimental evaluation indicates that the proposed data locality optimization scheme improves inter-core conflict misses in the shared cache by 67% on average when both allocation and scheduling are used. Also, the execution time improvements we achieve (29% on average) are very close to the optimal savings that could be achieved using a hypothetical scheme. Copyright 2009 ACM.Item Open Access Querying web metadata: Native score management and text support in databases(Association for Computing Machinery, 2004) Özsoyoǧlu, G.; Altingövde, I. S.; Al-Hamdani, A.; Özel, S. A.; Ulusoy, Özgür; Özsoyoǧlu, Z. M.In this article, we discuss the issues involved in adding a native score management system to object-relational databases, to be used in querying Web metadata (that describes the semantic content of Web resources). The Web metadata model is based on topics (representing entities), relationships among topics (called metalinks), and importance scores (sideway values) of topics and metalinks. We extend database relations with scoring functions and importance scores. We add to SQL score-management clauses with well-defined semantics, and propose the sidewayvalue algebra (SVA), to evaluate the extended SQL queries. SQL extensions and the SVA algebra are illustrated through two Web resources, namely, the DBLP Bibliography and the SIGMOD Anthology. SQL extensions include clauses for propagating input tuple importance scores to output tuples during query processing, clauses that specify query stopping conditions, threshold predicates (a type of approximate similarity predicates for text comparisons), and user-defined-function-based predicates. The propagated importance scores are then used to rank and return a small number of output tuples. The query stopping conditions are propagated to SVA operators during query processing. We show that our SQL extensions are well-defined, meaning that, given a database and a query Q, under any query processing scheme, the output tuples of Q and their importance scores stay the same. To process the SQL extensions, we discuss two sideway value algebra operators, namely, sideway value algebra join and topic closure, give their implementation algorithms, and report their experimental evaluations.Item Open Access Second chance: a hybrid approach for dynamic result caching and prefetching in search engines(Association for Computing Machinery, 2013-12) Ozcan, R.; Altingovde, I. S.; Cambazoglu, B. B.; Ulusoy, O.Web search engines are known to cache the results of previously issued queries. The stored results typically contain the document summaries and some data that is used to construct the final search result page returned to the user. An alternative strategy is to store in the cache only the result document IDs, which take much less space, allowing results of more queries to be cached. These two strategies lead to an interesting trade-off between the hit rate and the average query response latency. In this work, in order to exploit this trade-off, we propose a hybrid result caching strategy where a dynamic result cache is split into two sections: an HTML cache and a docID cache. Moreover, using a realistic cost model, we evaluate the performance of different result prefetching strategies for the proposed hybrid cache and the baseline HTML-only cache. Finally, we propose a machine learning approach to predict singleton queries, which occur only once in the query stream. We show that when the proposed hybrid result caching strategy is coupled with the singleton query predictor, the hit rate is further improved. © 2013 ACM.