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Displaying 1-11 out of 11 total
The Pairwise Gaussian Random Field for High-Dimensional Data Imputation
Found in: 2013 IEEE International Conference on Data Mining (ICDM)
By Zhuhua Cai,Christopher Jermaine,Zografoula Vagena,Dionysios Logothetis,Luis L. Perez
Issue Date:December 2013
pp. 61-70
In this paper, we consider the problem of imputation (recovering missing values) in very high-dimensional data with an arbitrary covariance structure. The modern solution to this problem is the Gaussian Markov random field (GMRF). The problem with applying...
 
Strongly consistent replication for a bargain
Found in: Data Engineering, International Conference on
By Konstantinos Krikellas, Sameh Elnikety, Zografoula Vagena, Orion Hodson
Issue Date:March 2010
pp. 52-63
Strong consistency is an important correctness property for replicated databases. It ensures that each transaction accesses the latest committed database state as provided in centralized databases. Achieving strong consistency in replicated databases is a ...
 
Distributed Top-K Query Processing in Wireless Sensor Networks
Found in: Mobile Data Management, IEEE International Conference on
By Demetrios Zeinalipour-Yazti, Zografoula Vagena
Issue Date:April 2008
pp. 227
Wireless Sensor Networks create an innovative technology that enables users to monitor and study the physical world at an extremely high resolution. Query processing in such ad-hoc environments is a challenging task due to the complexities imposed by the i...
   
RoXSum: Leveraging Data Aggregation and Batch Processing for XML Routing
Found in: Data Engineering, International Conference on
By Zografoula Vagena, Mirella M. Moro, Vassilis J. Tsotras
Issue Date:April 2007
pp. 1466-1470
Content-based routing is the primary form of communication within publish/subscribe systems. In those systems data transmission is performed by sophisticated overlay networks of content-based routers, which match data messages against registered subscripti...
 
Efficient Processing of XML Containment Queries Using Partition-Based Schemes
Found in: Database Engineering and Applications Symposium, International
By Zografoula Vagena, Mirella M. Moro, Vassilis J. Tsotras
Issue Date:July 2004
pp. 161-170
XML query languages provide facilities to query XML data both on their value as well as their structure. A basic operation in processing and optimizing such queries is the containment join, which takes two sets of elements and returns pairs of elements whe...
 
Supporting Branched Versions on XML Documents
Found in: Research Issues in Data Engineering, International Workshop on
By Zografoula Vagena, Mirella M. Moro, Vassilis J. Tsotras
Issue Date:March 2004
pp. 137-144
Many e-commerce and e-government applications are collaborative in nature (e.g. negotiation and e-catalog management). In collaborative environments, users typically define new document versions from any past version, which creates the need for supporting ...
 
Recovery from "bad" user transactions
Found in: Proceedings of the 2006 ACM SIGMOD international conference on Management of data (SIGMOD '06)
By David Lomet, Roger Barga, Zografoula Vagena
Issue Date:June 2006
pp. 337-346
User written transaction code is responsible for the "C" in ACID transactions, i.e., taking the database from one consistent state to the next. However, user transactions can be flawed and lead to inconsistent (or invalid) states. Database systems usually ...
     
Evaluating structural summaries as access methods for XML
Found in: Proceedings of the 15th international conference on World Wide Web (WWW '06)
By Mirella M. Moro, Vassilis J. Tsotras, Zografoula Vagena
Issue Date:May 2006
pp. 1079-1080
Structural summaries are data structures that preserve all structural features of XML documents in a compact form. We investigate the applicability of the most popular summaries as textitaccess methods within XML query processing. In this context, issues l...
     
Answering order-based queries over XML data
Found in: Special interest tracks and posters of the 14th international conference on World Wide Web (WWW '05)
By Divesh Srivastava, Nick Koudas, Vassilis J. Tsotras, Zografoula Vagena
Issue Date:May 2005
pp. 1162-1163
Order-based queries over XML data include XPath navigation axes such as following-sibling and following. In this paper, we present holistic algorithms that evaluate such order-based queries. An experimental comparison with previous approaches shows the per...
     
Twig query processing over graph-structured XML data
Found in: Proceedings of the 7th International Workshop on the Web and Databases: colocated with ACM SIGMOD/PODS 2004 (WebDB '04)
By Mirella M. Moro, Vassilis J. Tsotras, Zografoula Vagena
Issue Date:June 2004
pp. 43-48
XML and semi-structured data is usually modeled using graph structures. Structural summaries, which have been proposed to speedup XML query processing have graph forms as well. The existent approaches for evaluating queries over tree structured data (i.e. ...
     
Identifying similarities, periodicities and bursts for online search queries
Found in: Proceedings of the 2004 ACM SIGMOD international conference on Management of data (SIGMOD '04)
By Chris Meek, Dimitrios Gunopulos, Michail Vlachos, Zografoula Vagena
Issue Date:June 2004
pp. 131-142
We present several methods for mining knowledge from the query logs of the MSN search engine. Using the query logs, we build a time series for each query word or phrase (e.g., 'Thanksgiving' or 'Christmas gifts') where the elements of the time series are t...
     
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