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668 results on '"Papadias, Dimitris"'

1. Fast and Adaptive Bulk Loading of Multidimensional Points

Author

Moti, Moin Hussain and Papadias, Dimitris

Subjects
Computer Science - Databases
Abstract

Existing methods for bulk loading disk-based multidimensional points involve multiple applications of external sorting. In this paper, we propose techniques that apply linear scan, and are therefore significantly faster. The resulting FMBI Index possesses several desirable properties, including almost full and square nodes with zero overlap, and has excellent query performance. As a second contribution, we develop an adaptive version AMBI, which utilizes the query workload to build a partial index only for parts of the data space that contain query results. Finally, we extend FMBI and AMBI to parallel bulk loading and query processing in distributed systems. An extensive experimental evaluation with real datasets confirms that FMBI and AMBI clearly outperform competitors in terms of combined index construction and query processing cost, sometimes by orders of magnitude.

Published
2024

2. Uncertain Graph Sparsification

Author

Parchas, Panos, Papailiou, Nikolaos, Papadias, Dimitris, and Bonchi, Francesco

Subjects
Computer Science - Data Structures and Algorithms, Computer Science - Databases
Abstract

Uncertain graphs are prevalent in several applications including communications systems, biological databases and social networks. The ever increasing size of the underlying data renders both graph storage and query processing extremely expensive. Sparsification has often been used to reduce the size of deterministic graphs by maintaining only the important edges. However, adaptation of deterministic sparsification methods fails in the uncertain setting. To overcome this problem, we introduce the first sparsification techniques aimed explicitly at uncertain graphs. The proposed methods reduce the number of edges and redistribute their probabilities in order to decrease the graph size, while preserving its underlying structure. The resulting graph can be used to efficiently and accurately approximate any query and mining tasks on the original graph. An extensive experimental evaluation with real and synthetic datasets illustrates the effectiveness of our techniques on several common graph tasks, including clustering coefficient, page rank, reliability and shortest path distance.

Published
2016

3. Engineering Methods for Differentially Private Histograms: Efficiency Beyond Utility

Author

Kellaris, Georgios, Papadopoulos, Stavros, and Papadias, Dimitris

Subjects
Computer Science - Databases
Abstract

Publishing histograms with $\epsilon$-differential privacy has been studied extensively in the literature. Existing schemes aim at maximizing the utility of the published data, while previous experimental evaluations analyze the privacy/utility trade-off. In this paper we provide the first experimental evaluation of differentially private methods that goes beyond utility, emphasizing also on another important aspect, namely efficiency. Towards this end, we first observe that all existing schemes are comprised of a small set of common blocks. We then optimize and choose the best implementation for each block, determine the combinations of blocks that capture the entire literature, and propose novel block combinations. We qualitatively assess the quality of the schemes based on the skyline of efficiency and utility, i.e., based on whether a method is dominated on both aspects or not. Using exhaustive experiments on four real datasets with different characteristics, we conclude that there are always trade-offs in terms of utility and efficiency. We demonstrate that the schemes derived from our novel block combinations provide the best trade-offs for time critical applications. Our work can serve as a guide to help practitioners engineer a differentially private histogram scheme depending on their application requirements.

Published
2015

5. Indexing Metric Spaces

Author

Zezula, Pavel, Batko, Michal, Dohnal, Vlastislav, Papadias, Dimitris, Section editor, Liu, Ling, editor, and Özsu, M. Tamer, editor

Published
2018
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9. Grid File (and Family)

Author

Papadopoulos, Apostolos N., Manolopoulos, Yannis, Theodoridis, Yannis, Tsotras, Vassilis J., Papadias, Dimitris, Section editor, Liu, Ling, editor, and Özsu, M. Tamer, editor

Published
2018
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12. Closest-Pair Query

Author

Corral, Antonio, Vassilakopoulos, Michael, Papadias, Dimitris, Section Editor, Liu, Ling, editor, and Özsu, M. Tamer, editor

Published
2018
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13. Trip Planning Queries

Author

Hsueh, Yu-Ling, Zimmermann, Roger, Papadias, Dimitris, Section editor, Liu, Ling, editor, and Özsu, M. Tamer, editor

Published
2018
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16. Spatiotemporal Trajectories

Author

Frentzos, Elias, Theodoridis, Yannis, Papadopoulos, Apostolos N., Papadias, Dimitris, Section Editor, Liu, Ling, editor, and Özsu, M. Tamer, editor

Published
2018
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20. Spatial Join

Author

Mamoulis, Nikos, Papadias, Dimitris, Section Editor, Liu, Ling, editor, and Özsu, M. Tamer, editor

Published
2018
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21. Spatial Indexing Techniques

Author

Manolopoulos, Yannis, Theodoridis, Yannis, Tsotras, Vassilis J., Papadias, Dimitris, Section Editor, Liu, Ling, editor, and Özsu, M. Tamer, editor

Published
2018
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24. Spatial Data Mining

Author

Shekhar, Shashi, Jiang, Zhe, Kang, James, Gandhi, Vijay, Papadias, Dimitris, Section Editor, Liu, Ling, editor, and Özsu, M. Tamer, editor

Published
2018
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26. Spatial Anonymity

Author

Kalnis, Panos, Ghinita, Gabriel, Papadias, Dimitris, Section Editor, Liu, Ling, editor, and Özsu, M. Tamer, editor

Published
2018
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28. R-Tree (and Family)

Author

Papadopoulos, Apostolos N., Corral, Antonio, Nanopoulos, Alexandros, Theodoridis, Yannis, Papadias, Dimitris, Section editor, Liu, Ling, editor, and Özsu, M. Tamer, editor

Published
2018
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29. Road Networks

Author

Shahabi, Cyrus, Papadias, Dimitris, Section editor, Liu, Ling, editor, and Özsu, M. Tamer, editor

Published
2018
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33. Quadtrees (and Family)

Author

Vassilakopoulos, Michael, Tzouramanis, Theodoros, Papadias, Dimitris, Section Editor, Liu, Ling, editor, and Özsu, M. Tamer, editor

Published
2018
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36. Voronoi Diagrams

Author

Shahabi, Cyrus, Sharifzadeh, Mehdi, Papadias, Dimitris, Section editor, Liu, Ling, editor, and Özsu, M. Tamer, editor

Published
2018
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38. Geo-Social Keyword Search

Author

Ahuja, Ritesh, Armenatzoglou, Nikos, Papadias, Dimitris, Fakas, George J., Hutchison, David, Series editor, Kanade, Takeo, Series editor, Kittler, Josef, Series editor, Kleinberg, Jon M., Series editor, Mattern, Friedemann, Series editor, Mitchell, John C., Series editor, Naor, Moni, Series editor, Pandu Rangan, C., Series editor, Steffen, Bernhard, Series editor, Terzopoulos, Demetri, Series editor, Tygar, Doug, Series editor, Weikum, Gerhard, Series editor, Claramunt, Christophe, editor, Schneider, Markus, editor, Wong, Raymond Chi-Wing, editor, Xiong, Li, editor, Loh, Woong-Kee, editor, Shahabi, Cyrus, editor, and Li, Ki-Joune, editor

Published
2015
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39. Combining Differential Privacy and PIR for Efficient Strong Location Privacy

Author

Fung, Eric, Kellaris, Georgios, Papadias, Dimitris, Hutchison, David, Series editor, Kanade, Takeo, Series editor, Kittler, Josef, Series editor, Kleinberg, Jon M., Series editor, Mattern, Friedemann, Series editor, Mitchell, John C., Series editor, Naor, Moni, Series editor, Pandu Rangan, C., Series editor, Steffen, Bernhard, Series editor, Terzopoulos, Demetri, Series editor, Tygar, Doug, Series editor, Weikum, Gerhard, Series editor, Claramunt, Christophe, editor, Schneider, Markus, editor, Wong, Raymond Chi-Wing, editor, Xiong, Li, editor, Loh, Woong-Kee, editor, Shahabi, Cyrus, editor, and Li, Ki-Joune, editor

Published
2015
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41. Space-Filling Curves

Author

Mokbel, Mohamed F., Aref, Walid G., Papadias, Dimitris, Section Editor, Liu, Ling, editor, and Özsu, M. Tamer, editor

Published
2018
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42. Metric Space

Author

Zezula, Pavel, Batko, Michal, Dohnal, Vlastislav, Papadias, Dimitris, Section editor, Liu, Ling, editor, and Özsu, M. Tamer, editor

Published
2018
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44. Algorithms for Hierarchical Spatial Reasoning (96-2)

Author

Papadias, Dimitris and Egenhofer, Max

Subjects
spatial reasoning, geographic databases, GIS, direction relations, path consistency
Abstract

In several applications, there is the need to reason about spatial relations using multiple local frames of reference organized in aggregation hierarchies. In this paper we deal with direction relations, a special class of spatial relations that describe order in space (e.g., north, northeast). We assume a spatial database of points and regions. Points belong to regions, which may be parts of larger regions and so on. The direction relations between points in the same region are explicitly represented. Inference mechanisms are applied to extract the relation between points in different regions and detect inconsistencies. We study two complementary types of inference. The first one derives the relation between two points that exist in different regions through chains of common points using path consistency. The second type of inference uses the relation between ancestor regions to infer the relation between the points. The paper describes algorithms for both types of inference and discusses their computational complexity.

Published
1996

45. Direction Relations and Two-Dimensional Range Queries: Optimization Techniques (95-9)

Author

Yannis, Theodoridis, Papadias, Dimitris, Stefanakis, Emmanuel, and Sellis, Timos

Subjects
spatial databases, direction relations, range queries, data structures, performance analysis, query optimisation
Abstract

Despite the attention that direction relations, such as east, southeast etc., have attracted in several domains related to Spatial Databases and Geographic Information Systems (GIS), little work has been done on their formalization and efficient processing. In this paper we define direction relations between two-dimensional objects in different levels of qualitative resolution and we show how these relations can be efficiently retrieved in existing DBMSs using B- , KDB- and R- tree-based data structures. Since query processing involving direction relations maps into range queries in two- dimensional space, our work essentially studies optimization techniques for 2D ranges. We test the efficiency of alternative indexing methods through extensive experimentation and we present analytical models that estimate their performance. The analytical estimates are proved to be very close to the actual results and can be used by spatial query optimizers in order to decide the appropriate data structure for each type of range query. Although for our experiments we define a small set of representative relations motivated by geographic applications, the results of this paper are directly applicable to any type of direction relations (or range queries in general) that may arise in different application domains.

Published
1995

46. Waffle

Author

Moti, Moin Hussain, primary, Simatis, Panagiotis, additional, and Papadias, Dimitris, additional

Published
2022
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47. Topological Relations in the World of Minimum Bounding Rectangles: a Study with R-trees (94-8)

Author

Papadias, Dimitris, Theodoridis, Yannis, Sellis, Timos, and Egenhofer, Max J.

Subjects
spatial analysis, spatial query, spatial database, topological relations
Abstract

Recent developments in spatial relations have led to their use in numerous applications involving spatial databases. This paper is concerned with the retrieval of topological relations in Minimum Bounding Rectangle-based data structures. We study the topological information that Minimum Bounding Rectangles convey about the actual objects they enclose, using the concept of projections. Then we apply the results in R-trees and their variations, R+ and R* trees in order to minimize disk accesses for queries involving topological relations. We also investigate queries that involve complex spatial conditions in the form of disjunctions and conjunctions and we discuss possible extensions.

Published
1994

48. Location-Based Sponsored Search Advertising

Author

Trimponias, George, Bartolini, Ilaria, Papadias, Dimitris, Hutchison, David, editor, Kanade, Takeo, editor, Kittler, Josef, editor, Kleinberg, Jon M., editor, Mattern, Friedemann, editor, Mitchell, John C., editor, Naor, Moni, editor, Nierstrasz, Oscar, editor, Pandu Rangan, C., editor, Steffen, Bernhard, editor, Sudan, Madhu, editor, Terzopoulos, Demetri, editor, Tygar, Doug, editor, Vardi, Moshe Y., editor, Weikum, Gerhard, editor, Nascimento, Mario A., editor, Sellis, Timos, editor, Cheng, Reynold, editor, Sander, Jörg, editor, Zheng, Yu, editor, Kriegel, Hans-Peter, editor, Renz, Matthias, editor, and Sengstock, Christian, editor

Published
2013
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