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Displaying 1-45 out of 45 total
CHOROCHRONOS -- Research on Spatiotemporal Database Systems
Found in: Database and Expert Systems Applications, International Workshop on
By Timos Sellis
Issue Date:September 1999
pp. 452
Spatiotemporal database management systems can become an enabling technology for important applications such as Geographic Information Systems (GIS), environmental information systems, and multimedia. In this paper we address research issues in spatiotempo...
 
Multi-granular Time-Based Sliding Windows over Data Streams
Found in: Temporal Representation and Reasoning, International Syposium on
By Kostas Patroumpas, Timos Sellis
Issue Date:September 2010
pp. 146-153
We introduce a multi-level window operator that concurrently spans temporal extents of increasing granularity over a streaming dataset. This windowing construct is inherently sliding with time, essentially providing at each granularity a varying, but alway...
 
Serving the Sky: Discovering and Selecting Semantic Web Services through Dynamic Skyline Queries
Found in: International Conference on Semantic Computing
By Dimitrios Skoutas, Dimitris Sacharidis, Alkis Simitsis, Timos Sellis
Issue Date:August 2008
pp. 222-229
Semantic Web service descriptions are typically multi-parameter constructs. Discovering semantically relevant services given a desirable service description is typically addressed by performing a pairwise, logic-based match between the requested and offere...
 
A Simulator for a Mobile Peer-to-Peer Database Environment
Found in: Mobile Data Management, IEEE International Conference on
By Verena Kantere, Konstantina Palla, Kostas Patroumpas, Timos Sellis
Issue Date:April 2008
pp. 223-224
We present a simulation environment that can be employed to study P2P mobile networks that are fast-evolving in both their topology and their content. This simulator implements a proposed P2P architecture based on Mobile Agent and Active Database technolog...
 
Correction to
Found in: IEEE Transactions on Knowledge and Data Engineering
By Spiros Skiadopoulos, Nikos Sarkas, Timos Sellis, Manolis Koubarakis
Issue Date:October 2007
pp. 1448
No summary available.
 
A Ranking Mechanism for SemanticWeb Service Discovery
Found in: Services, IEEE Congress on
By Dimitrios Skoutas, Alkis Simitsis, Timos Sellis
Issue Date:July 2007
pp. 41-48
This paper presents an approach for ranking semantic Web service advertisements with respect to a service request. The use of recall and precision is proposed as suitable measures for determining the degree of match between the request and the advertisemen...
 
Semantics of Spatially-Aware Windows Over Streaming Moving Objects
Found in: Mobile Data Management, IEEE International Conference on
By Kostas Patroumpas, Timos Sellis
Issue Date:May 2007
pp. 52-59
No summary available.
 
Sampling Trajectory Streams with Spatiotemporal Criteria
Found in: Scientific and Statistical Database Management, International Conference on
By Michalis Potamias, Kostas Patroumpas, Timos Sellis
Issue Date:July 2006
pp. 275-284
Monitoring movement of high-dimensional points is essential for environmental databases, geospatial applications, and biodiversity informatics as it reveals crucial information about data evolution, provenance detection, pattern matching etc. Despite recen...
 
Containment of Partially Specified Tree-Pattern Queries
Found in: Scientific and Statistical Database Management, International Conference on
By Dimitri Theodoratos, Theodore Dalamagas, Pawel Placek, Stefanos Souldatos, Timos Sellis
Issue Date:July 2006
pp. 3-12
<p>Nowadays, huge volumes of data, including scientific data, are organized or exported in tree-structured form. Querying capabilities are provided through tree-pattern queries. The need for integrating multiple data sources with different tree struc...
 
DOMProxy: Enabling Dynamic-Content Front-end Web Caching
Found in: Web Content Caching and Distribution, International Workshop on
By Manolis Veliskakis, John Roussos, Panos Georgantas, Timos Sellis
Issue Date:September 2005
pp. 56-61
<p>Proxy caching is a commonly accepted methodology used to reduce Internet traffic, decrease back-end related user delays, and generally improve web performance. Nevertheless, it seems to be inadequate when it comes to caching dynamic web pages, due...
 
Optimizing ETL Processes in Data Warehouses
Found in: Data Engineering, International Conference on
By Alkis Simitsis, Panos Vassiliadis, Timos Sellis
Issue Date:April 2005
pp. 564-575
Extraction-Transformation-Loading (ETL) tools are pieces of software responsible for the extraction of data from several sources, their cleansing, customization and insertion into a data warehouse. Usually, these processes must be completed in a certain ti...
 
STEDEL: A LANGUAGE FOR INTERACTIVE SPATIOTEMPORAL COMPOSITIONS
Found in: Multimedia and Expo, IEEE International Conference on
By Iosif Lazaridis, Michalis Vazirgiannis, Timos Sellis
Issue Date:August 2001
pp. 136
The two fundamental challenges in Virtual Reality over the WWW are (i) to facilitate the process of creating convincing, non-trivial, highly interactive and maintainable content and (ii) to efficiently deliver this content to the client with QoS guarantees...
 
Answering Multidimensional Queries on Cubes Using Other Cubes
Found in: Scientific and Statistical Database Management, International Conference on
By Dimitri Theodoratos, Timos Sellis
Issue Date:July 2000
pp. 109
Recently there is an important interest on On-Line Analytical Processing (OLAP) technology. In this context, in order to facilitate complex analysis, data are usually modeled multidimensionally, where multiple hierarchies are associated with the dimensions...
 
Experimental Evaluation of Data Warehouse Configuration Algorithms
Found in: Database and Expert Systems Applications, International Workshop on
By Spyros Ligoudistianos, Dimitri Theodoratos, Timos Sellis
Issue Date:August 1998
pp. 218
A Data Warehouse (DW) can be seen as a set of materialized views defined over relations that are stored in remote heterogeneous database systems. When a query is posed to the DW, it is evaluated locally, using only the materialized views. The DW configurat...
 
Specifications for Efficient Indexing in Spatiotemporal Databases
Found in: Scientific and Statistical Database Management, International Conference on
By Yannis Theodoridis, Timos Sellis, Apostolos N. Papadopoulos, Yannis Manolopoulos
Issue Date:April 1998
pp. 123
A new issue that arises in modern applications involves the efficient manipulation of (static or moving) spatial objects, and the relationships among them. As a result, modern database systems should be able to efficiently support that type of data. Toward...
 
Processing and Evaluating Partial Tree Pattern Queries on XML Data
Found in: IEEE Transactions on Knowledge and Data Engineering
By Xiaoying Wu,Stefanos Souldatos,Dimitri Theodoratos,Theodore Dalamagas,Yannis Vassiliou,Timos Sellis
Issue Date:December 2012
pp. 2244-2259
XML query languages typically allow the specification of structural patterns using XPath. Usually, these structural patterns are in the form of trees (Tree-Pattern Queries&#x2014;TPQs). Finding the occurrences of such patterns in an XML tree is a key o...
 
Evaluating Path Queries over Frequently Updated Route Collections
Found in: IEEE Transactions on Knowledge and Data Engineering
By Panagiotis Bouros,Dimitris Sacharidis,Theodore Dalamagas,Spiros Skiadopoulos,Timos Sellis
Issue Date:July 2012
pp. 1276-1290
The recent advances in the infrastructure of Geographic Information Systems (GIS), and the proliferation of GPS technology, have resulted in the abundance of geodata in the form of sequences of points of interest (POIs), waypoints, etc. We refer to sets of...
 
Ranking and Clustering Web Services Using Multicriteria Dominance Relationships
Found in: IEEE Transactions on Services Computing
By Dimitrios Skoutas, Dimitris Sacharidis, Alkis Simitsis, Timos Sellis
Issue Date:July 2010
pp. 163-177
As the web is increasingly used not only to find answers to specific information needs but also to carry out various tasks, enhancing the capabilities of current web search engines with effective and efficient techniques for web service retrieval and selec...
 
Probabilistic contextual skylines
Found in: Data Engineering, International Conference on
By Dimitris Sacharidis, Anastasios Arvanitis, Timos Sellis
Issue Date:March 2010
pp. 273-284
The skyline query returns the most interesting tuples according to a set of explicitly defined preferences among attribute values. This work relaxes this requirement, and allows users to pose meaningful skyline queries without stating their choices. To com...
 
Storing and Indexing Spatial Data in P2P Systems
Found in: IEEE Transactions on Knowledge and Data Engineering
By Verena Kantere, Spiros Skiadopoulos, Timos Sellis
Issue Date:February 2009
pp. 287-300
The peer-to-peer (P2P) paradigm has become very popular for storing and sharing information in a totally decentralized manner. At first, research focused on P2P systems that host 1D data. Nowadays, the need for P2P applications with multidimensional data h...
 
A Family of Directional Relation Models for Extended Objects
Found in: IEEE Transactions on Knowledge and Data Engineering
By Spiros Skiadopoulos, Nikos Sarkas, Timos Sellis, Manolis Koubarakis
Issue Date:August 2007
pp. 1116-1130
In this paper, we introduce a family of expressive models for qualitative spatial reasoning with directions. The proposed family is based on the cognitive plausible cone-based model. We formally define the directional relations that can be expressed in eac...
 
Computing and Managing Cardinal Direction Relations
Found in: IEEE Transactions on Knowledge and Data Engineering
By Spiros Skiadopoulos, Christos Giannoukos, Nikos Sarkas, Panos Vassiliadis, Timos Sellis, Manolis Koubarakis
Issue Date:December 2005
pp. 1610-1623
Qualitative spatial reasoning forms an important part of the commonsense reasoning required for building intelligent Geographical Information Systems (GIS). Previous research has come up with models to capture cardinal direction relations for typical GIS d...
 
State-Space Optimization of ETL Workflows
Found in: IEEE Transactions on Knowledge and Data Engineering
By Alkis Simitsis, Panos Vassiliadis, Timos Sellis
Issue Date:October 2005
pp. 1404-1419
Extraction-Transformation-Loading (ETL) tools are pieces of software responsible for the extraction of data from several sources, their cleansing, customization, and insertion into a data warehouse. In this paper, we delve into the logical optimization of ...
 
Efficient Cost Models for Spatial Queries Using R-Trees
Found in: IEEE Transactions on Knowledge and Data Engineering
By Yannis Theodoridis, Emmanuel Stefanakis, Timos Sellis
Issue Date:January 2000
pp. 19-32
<p><b>Abstract</b>—Selection and join queries are fundamental operations in Data Base Management Systems (DBMS). Support for nontraditional data, including spatial objects, in an efficient manner is of ongoing interest in database researc...
 
Panel on Data Warehouse Quality Issues
Found in: Cooperative Information Systems, IFCIS International Conference on
By Yannis Vassiliou, Timos Sellis, Matthias Jarke, Eric Simon
Issue Date:September 1999
pp. 8
In contemporary organizations, inaccurate, invalid, out-of-date or incomplete data may have a heavy financial, or even social impact. Consequently, the problem arises how to design and construct data warehouses, which satisfy specific, well-defined quality...
 
Specifying and Authoring Multimedia Scenarios
Found in: IEEE Multimedia
By Michalis Vazirgiannis, Ioannis Kostalas, Timos Sellis
Issue Date:July 1999
pp. 24-37
An authoring methodology and a set of checking tools let authors specify the spatial and temporal features of an application and verify the application prior to its execution. The checking tools include an animation tool, spatial and temporal layouts, and ...
 
Flexible and Adaptable Buffer Management Techniques for Database Management Systems
Found in: IEEE Transactions on Computers
By Raymond Ng, Christos Faloutsos, Timos Sellis
Issue Date:April 1995
pp. 546-560
<p><it>Abstract</it>—The problem of buffer management in database management systems is concerned with the efficient main memory allocation and management for answering database queries. Previous works on buffer allocation are based eithe...
 
Combining Hierarchy Encoding and Pre-Grouping: Intelligent Grouping in Star Join Processing
Found in: Data Engineering, International Conference on
By Roland Pieringer, Klaus Elhardt, Frank Ramsak, Volker Markl, Robert Fenk, Rudolf Bayer, Nikos Karayannidis, Aris Tsois, Timos Sellis
Issue Date:March 2003
pp. 329
Efficient star query processing is crucial for a performant data warehouse (DW) implementation and much work is available on physical optimization (e.g., indexing and schema design) and logical optimization (e.g., pre-aggregated materialized views with que...
 
Learning to rank user intent
Found in: Proceedings of the 20th ACM international conference on Information and knowledge management (CIKM '11)
By Giorgos Giannopoulos, Theodore Dalamagas, Timos Sellis, Ulf Brefeld
Issue Date:October 2011
pp. 195-200
Personalized retrieval models aim at capturing user interests to provide personalized results that are tailored to the respective information needs. User interests are however widely spread, subject to change, and cannot always be captured well, thus rende...
     
Efficient answering of set containment queries for skewed item distributions
Found in: Proceedings of the 14th International Conference on Extending Database Technology (EDBT/ICDT '11)
By Manolis Terrovitis, Nikos Mamoulis, Panagiotis Bouros, Panos Vassiliadis, Timos Sellis
Issue Date:March 2011
pp. 225-236
In this paper we address the problem of efficiently evaluating containment (i.e., subset, equality, and superset) queries over set-valued data. We propose a novel indexing scheme, the Ordered Inverted File (OIF) which, differently from the state-of-the-art...
     
On enhancing scalability for distributed RDF/S stores
Found in: Proceedings of the 14th International Conference on Extending Database Technology (EDBT/ICDT '11)
By Dimitris Sacharidis, George Tsatsanifos, Timos Sellis
Issue Date:March 2011
pp. 141-152
This work presents MIDAS-RDF, a distributed P2P RDF/S repository that is built on top of a distributed multi-dimensional index structure. MIDAS-RDF features fast retrieval of RDF triples satisfying various pattern queries by translating them into multi-dim...
     
A tool for mapping discovery over revealing schemas
Found in: Proceedings of the 12th International Conference on Extending Database Technology: Advances in Database Technology (EDBT '09)
By Dimos Bousounis, Timos Sellis, Verena Kantere
Issue Date:March 2009
pp. 94-104
In a world of wide-scale information sharing, the decentralized coordination has to consolidate a variety of heterogeneity. Shared data are described in different formats, i.e. data structures, values and schemas. Querying manifold such sources entails tec...
     
Top-k dominant web services under multi-criteria matching
Found in: Proceedings of the 12th International Conference on Extending Database Technology: Advances in Database Technology (EDBT '09)
By Alkis Simitsis, Dimitrios Skoutas, Dimitris Sacharidis, Timos Sellis, Verena Kantere
Issue Date:March 2009
pp. 94-104
As we move from a Web of data to a Web of services, enhancing the capabilities of the current Web search engines with effective and efficient techniques for Web services retrieval and selection becomes an important issue. Traditionally, the relevance of a ...
     
Monitoring continuous queries over streaming locations
Found in: Proceedings of the 16th ACM SIGSPATIAL international conference on Advances in geographic information systems (GIS '08)
By Evi Kefallinou, Kostas Patroumpas, Timos Sellis
Issue Date:November 2008
pp. 1-8
We report on our experience from design and implementation of a powerful map application for managing, querying and visualizing evolving locations of moving objects. Instead of building a specialized spatiotemporal database, we have chosen to retain geogra...
     
Boosting the ranking function learning process using clustering
Found in: Proceeding of the 10th ACM workshop on Web information and data management (WIDM '08)
By Giorgos Giannopoulos, Magdalini Eirinaki, Theodore Dalamagas, Timos Sellis
Issue Date:October 2008
pp. 1-2
As the Web continuously grows, the results returned by search engines are too many to review. Lately, the problem of personalizing the ranked result list based on user feedback has gained a lot of attention. Such approaches usually require a big amount of ...
     
A heuristic approach for checking containment of generalized tree-pattern queries
Found in: Proceeding of the 17th ACM conference on Information and knowledge mining (CIKM '08)
By Dimitri Theodoratos, Pawel Placek, Stefanos Souldatos, Theodore Dalamagas, Timos Sellis
Issue Date:October 2008
pp. 1001-1001
Query processing techniques for XML data have focused mainly on tree-pattern queries (TPQs). However, the need for querying XML data sources whose structure is very complex or not fully known to the user, and the need to integrate multiple XML data sources...
     
Efficient evaluation of generalized path pattern queries on XML data
Found in: Proceeding of the 17th international conference on World Wide Web (WWW '08)
By Dimitri Theodoratos, Stefanos Souldatos, Theodore Dalamagas, Timos Sellis, Xiaoying Wu
Issue Date:April 2008
pp. 1-7
Finding the occurrences of structural patterns in XML data is a key operation in XML query processing. Existing algorithms for this operation focus almost exclusively on path-patterns or tree-patterns. Requirements in flexible querying of XML data have mot...
     
On-line discovery of hot motion paths
Found in: Proceedings of the 11th international conference on Extending database technology: Advances in database technology (EDBT '08)
By Dimitris Sacharidis, Kostas Patroumpas, Kyriakos Mouratidis, Manolis Terrovitis, Michalis Potamias, Timos Sellis, Verena Kantere
Issue Date:March 2008
pp. 1-3
We consider an environment of numerous moving objects, equipped with location-sensing devices and capable of communicating with a central coordinator. In this setting, we investigate the problem of maintaining hot motion paths, i.e., routes frequently foll...
     
Approximate order-k Voronoi cells over positional streams
Found in: Proceedings of the 15th annual ACM international symposium on Advances in geographic information systems (GIS '07)
By Kostas Patroumpas, Theofanis Minogiannis, Timos Sellis
Issue Date:November 2007
pp. 1-89
Handling streams of positional updates from numerous moving objects has become a challenging task for many monitoring applications. Several algorithms have been recently proposed for providing exact answers particularly to continuous range and k-nearest ne...
     
Handling spatial data in distributed environments
Found in: Proceedings of the 15th annual ACM international symposium on Advances in geographic information systems (GIS '07)
By Timos Sellis, Verena Kantere
Issue Date:November 2007
pp. 1-89
Handling spatial data in distributed environments is an intriguing issue. We consider autonomous sites of an overlay network that are bound to specific spatial information. We assume that each site has partial knowledge of the overlay. Actually, the sites ...
     
The Lowell database research self-assessment
Found in: Communications of the ACM
By Alon Halevy, Avi Silberschatz, Bruce Croft, David DeWitt, David Maier, Dieter Gawlick, Gerhard Weikum, Hans Schek, Hector Garcia Molina, Jeff Naughton, Jeff Ullman, Jennifer Widom, Jim Gray, Joe Hellerstein, Laura Haas, Martin Kersten, Michael Pazzani, Mike Carey, Mike Franklin, Mike Lesk, Mike Stonebraker, Phil Bernstein, Rakesh Agrawal, Rick Snodgrass, Serge Abiteboul, Stan Zdonik, Stefano Ceri, Timos Sellis, Yannis Ioannidis
Issue Date:May 2005
pp. 111-118
Database needs are changing, driven by the Internet and increasing amounts of scientific and sensor data. In this article, the authors propose research into several important new directions for database management systems.
     
A model for the prediction of R-tree performance
Found in: Proceedings of the fifteenth ACM SIGACT-SIGMOD-SIGART symposium on Principles of database systems (PODS '96)
By Timos Sellis, Yannis Theodoridis
Issue Date:June 1996
pp. 161-171
The goal of the Garlic [1] project is to build a multimedia information system capable of integrating data that resides in different database systems as well as in a variety of non-database data servers. This integration must be enabled while maintaining t...
     
Topological relations in the world of minimum bounding rectangles: a study with R-trees
Found in: Proceedings of the 1995 ACM SIGMOD international conference on Management of data (SIGMOD '95)
By Dimitris Papadias, Max J. Egenhofer, Timos Sellis, Yannis Theodoridis
Issue Date:May 1995
pp. 219-230
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 topol...
     
Flexible buffer allocation based on marginal gains
Found in: Proceedings of the 1991 ACM SIGMOD international conference on Management of data (SIGMOD '91)
By Christos Faloutsos, Raymond Ng, Timos Sellis
Issue Date:May 1991
pp. 328-340
Iris is an object-oriented database management system being developed at Hewlett-Packard Laboratories [1], [3]. This videotape provides an overview of the Iris data model and a summary of our experiences in converting a computer-integrated manufacturing ap...
     
Analysis of object oriented spatial access methods
Found in: Proceedings of the 1987 ACM SIGMOD international conference on Management of data (SIGMOD '87)
By Christos Faloutsos, Nick Roussopoulos, Timos Sellis
Issue Date:May 1987
pp. 349-362
This paper provides an analysis of R-trees and a variation (R+-trees) that avoids overlapping rectangles in intermediate nodes of the tree. The main contributions of the paper are the following. We provide the first known analysis of R-trees. Although form...
     
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