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Vassilios S. Verykios

dblp:94/1028 · also Vasileios S. Verykios · DBLP profile ↗
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59ranked-venue papers
6as first author
11since 2021 · last 2026
0000-0002-9758-0819ORCID · verified

Domains — the database's venue-derived domains; a paper can count in several

Databases, data management, data science and information retrieval · 40 · 4 first-author · 8 since 2021Artificial intelligence and machine learning · 19 · 1 first-author · 4 since 2021Applied, interdisciplinary, general and emerging computing · 5 · 1 since 2021Security and privacy · 4Human-computer interaction and ubiquitous computing · 3 · 1 first-authorSystems, architecture and hardware · 1Graphics, computer vision, multimedia, augmented reality and games · 1Theory of computation · 1

Expertise — from the expertise taxonomy: the topics of the expert's papers under the CCF categories. A weight counts papers with recency: 1 for a paper about the topic, 0.3 when the topic is its context, halved every five years.

Databases, data mining, and information retrieval
12 papers
Data integration and cleaning · 46% Knowledge graphs · 33% Data stream processing · 8%
Network and information security
5 papers
Privacy and data protection · 95% Cryptographic protocols and secure computation · 5%

Topics — the 21 heaviest of 22, each with the papers that count most for it

TopicWeightPapersLastEvidence papers
Knowledge graphs
entity linking
2.372024
A Suite of Efficient Randomized Algorithms for Streaming Record Linkage · IEEE Trans. Knowl. Data Eng. 2024
A Randomized Blocking Structure for Streaming Record Linkage · Proc. VLDB Endow. 2023
Distance-Aware Encoding of Numerical Values for Privacy-Preserving Record Linkage · ICDE 2017
Data integration and cleaning › entity resolution
blocking
1.632024
A Suite of Efficient Randomized Algorithms for Streaming Record Linkage · IEEE Trans. Knowl. Data Eng. 2024
A Randomized Blocking Structure for Streaming Record Linkage · Proc. VLDB Endow. 2023
An LSH-Based Blocking Approach with a Homomorphic Matching Technique for Privacy-Preserving Record Linkage · IEEE Trans. Knowl. Data Eng. 2015
Data integration and cleaning
entity resolution
1.022026
ALER: An Active Learning Hybrid System for Efficient Entity Resolution · Proc. VLDB Endow. 2026
Duplicate Record Detection: A Survey · IEEE Trans. Knowl. Data Eng. 2007
Data integration and cleaning › entity resolution
active learning for entity matching
1.012026
ALER: An Active Learning Hybrid System for Efficient Entity Resolution · Proc. VLDB Endow. 2026
Privacy and data protection
privacy-preserving record linkage
0.832018
FEDERAL: A Framework for Distance-Aware Privacy-Preserving Record Linkage · IEEE Trans. Knowl. Data Eng. 2018
Distance-Aware Encoding of Numerical Values for Privacy-Preserving Record Linkage · ICDE 2017
Scalable Blocking for Privacy Preserving Record Linkage · KDD 2015
Knowledge graphs › entity linking
privacy-preserving record linkage
0.522017
Distance-Aware Encoding of Numerical Values for Privacy-Preserving Record Linkage · ICDE 2017
An LSH-Based Blocking Approach with a Homomorphic Matching Technique for Privacy-Preserving Record Linkage · IEEE Trans. Knowl. Data Eng. 2015
Privacy and data protection
anonymization
0.312018
FEDERAL: A Framework for Distance-Aware Privacy-Preserving Record Linkage · IEEE Trans. Knowl. Data Eng. 2018
Machine learning and data management
active learning
0.312026
ALER: An Active Learning Hybrid System for Efficient Entity Resolution · Proc. VLDB Endow. 2026
Machine learning and data management › human-in-the-loop
interactive learning
0.312026
ALER: An Active Learning Hybrid System for Efficient Entity Resolution · Proc. VLDB Endow. 2026
Indexing and storage engines
in-memory index
0.212023
A Randomized Blocking Structure for Streaming Record Linkage · Proc. VLDB Endow. 2023
Data integration and cleaning › entity resolution
duplicate detection
0.122007
Duplicate Record Detection: A Survey · IEEE Trans. Knowl. Data Eng. 2007
TAILOR: A Record Linkage Tool Box · ICDE 2002
Data mining › pattern mining › itemset mining
frequent itemset mining
0.112009
Exact Knowledge Hiding through Database Extension · IEEE Trans. Knowl. Data Eng. 2009
Data mining
pattern mining
0.112009
Exact Knowledge Hiding through Database Extension · IEEE Trans. Knowl. Data Eng. 2009
Privacy and data protection › privacy-preserving data analysis
privacy-preserving data mining
0.112009
Exact Knowledge Hiding through Database Extension · IEEE Trans. Knowl. Data Eng. 2009
Information retrieval
similarity measure
0.112007
Duplicate Record Detection: A Survey · IEEE Trans. Knowl. Data Eng. 2007
Cryptographic protocols and secure computation › secure query processing
encrypted matching
0.112015
Scalable Blocking for Privacy Preserving Record Linkage · KDD 2015
Data mining › pattern mining
association rule mining
0.012004
Association Rule Hiding · IEEE Trans. Knowl. Data Eng. 2004
Privacy and data protection › privacy-preserving data analysis › privacy-preserving data mining
association rule hiding
0.012004
Association Rule Hiding · IEEE Trans. Knowl. Data Eng. 2004
Data integration and cleaning › entity resolution
record matching
0.012003
A Bayesian decision model for cost optimal record matching · VLDB J. 2003
Mathematical optimization
integer programming
0.012009
Exact Knowledge Hiding through Database Extension · IEEE Trans. Knowl. Data Eng. 2009
Database theory
confidentiality
0.012004
Association Rule Hiding · IEEE Trans. Knowl. Data Eng. 2004

Methods — techniques the papers use, named apart from their topics

hybrid matching · 1.0active learning · 1.0locality-sensitive hashing · 1.0randomized algorithm · 0.8rolling record renewal · 0.7randomized block replacement · 0.7embedding · 0.7distance computation · 0.7distance-preserving embedding · 0.6hash functions · 0.3hash function · 0.3reference sets · 0.2multi-sampling transitive closure · 0.2constraint satisfaction · 0.2border-based approach · 0.2binary integer programming · 0.2hiding algorithm · 0.0
YearPublicationVenuePosition
2026 DynaHash: An efficient blocking structure for streaming record linkage
abstract
Record linkage holds a crucial position in data management and analysis by identifying and merging records from disparate data sets that pertain to the same real-world entity. As data volumes grow, the intricacies of record linkage amplify, presenting challenges, such as potential redundancies and computational complexities. This paper introduces DynaHash, a novel randomized record linkage mechanism that utilizes (a) the MinHash technique to generate compact representations of blocking keys and (b) Hamming Locality-Sensitive Hashing (LSH) to construct the blocking structure from these vectors. By employing these methods, DynaHash offers theoretical guarantees of accuracy and achieves sublinear runtime complexities, with appropriate parameter tuning. It comprises two key components: a persistent storage system for permanently storing the blocking structure to ensure complete results, and an in-memory component for generating very fast partial results by summarizing the persisted blocking structure. Additionally, DynaHash leverages Multi-Probe matching to scan multiple neighboring blocks, in terms of their Hamming distances, in order to find matches. Our theoretical work derives a decrease factor in the space requirements, which depends on the Hamming threshold, compared with the baseline LSH. Our experimental evaluation against three state-of-the-art methods on six real-world data sets demonstrates DynaHash’s exceptional recall rates and query times, which are at least 2 × faster than its competitors and do not depend on the size of the underlying data sets.
Dimitrios Karapiperis, Christos Tjortjis, Vassilios S. Verykios
Inf. Syst.3
2026 ALER: An Active Learning Hybrid System for Efficient Entity Resolution
Dimitrios Karapiperis, Leonidas Akritidis, Panayiotis Bozanis, Vassilios S. Verykios
Proc. VLDB Endow.4
2025 LSBlock: A Hybrid Blocking System Combining Lexical and Semantic Similarity Search for Record Linkage
Dimitrios Karapiperis, Christos Tjortjis, Vassilios S. Verykios
ADBIS3
2024 An end-to-end knowledge graph solution to the frequent itemset hiding problem
Panteleimon Krasadakis, Giuseppe Futia, Vassilios S. Verykios, Evangelos Sakkopoulos
Inf. Sci.3
2024 A Suite of Efficient Randomized Algorithms for Streaming Record Linkage
abstract
Organizations leverage massive volumes of information and new types of data to generate unprecedented insights and improve their outcomes. Correctly identifying duplicate records that represent the same entity, such as user, customer, patient and so on, a process commonly known as record linkage, can improve service levels, accelerate sales, or elevate healthcare decision support. Towards this direction, blocking methods are used with the aim to group matching records in the same block using a combination of their attributes as blocking keys. This paper introduces a suite of randomized algorithms specifically crafted for streaming record linkage settings. Using a bounded in-memory data structure, in terms of the number of blocks and positions within each block, our algorithms guarantee that the most frequently accessed and the most recently used blocks remain in main memory and, additionally, the records within a block are renewed on a rolling basis. The operation of our algorithms rely on simple random choices, instead of utilizing cumbersome sorting data structures, which ensure that the probability of inactive blocks and older records to remain in main memory decays in order to free space for more promising blocks and fresher records, respectively. We also introduce an algorithm that performs approximate blocking to tackle the problem of misspellings and typos present in the blocking keys. The experimental evaluation showcases that our proposed algorithms scale efficiently to data streams by providing certain accuracy guarantees.
Dimitrios Karapiperis, Christos Tjortjis, Vassilios S. Verykios
IEEE Trans. Knowl. Data Eng.3
2023 Graph based Hiding of Sensitive Knowledge
abstract
The Frequent Itemset Hiding Problem (FIHP) is an important research topic in the field of Privacy-Preserving Data Mining. Knowledge Graphs (KGs) have also recently emerged as a popular data representation model for various applications. However, the integration of KGs and FIHP is a relatively unexplored area of research. In this paper, we propose a novel approach to address the FIHP by incorporating Community Detection graph-based algorithms to hide sensitive knowledge in our data. Our approach preserves the structure and utility of the KG and efficiently produces the set of Itemsets that must be hidden. We evaluate our approach on popular FIHP datasets and demonstrate its effectiveness in terms of time efficiency.
Panteleimon Krasadakis, Giuseppe Futia, Vassilios S. Verykios, Evangelos Sakkopoulos
ICTAI3
2023 A Randomized Blocking Structure for Streaming Record Linkage
abstract
A huge amount of data, in terms of streams, are collected nowadays via a variety of sources, such as sensors, mobile devices, or even raw log files. The unprecedented rate at which these data are generated and collected calls for novel record linkage methods to identify matching records pairs, which refer to the same real-world entity. Towards this direction, blocking methods are used in order to reduce the number of candidate record pairs while still maintaining high levels of accuracy. This paper introduces ExpBlock, a randomized record linkage structure, which guarantees that both the most frequently accessed and recently used blocks remain in main memory and, additionally, the records within a block are renewed on a rolling basis. Specifically, the probability of inactive blocks and older records to remain in main memory decays in order to make room for more promising blocks and fresher records, respectively. We implement these features using random choices instead of utilizing cumbersome sorting data structures in order to favour simplicity of implementation and efficiency. We showcase, through the experimental evaluation, that ExplBlock scales efficiently to data streams by providing accurate results in a timely fashion.
Dimitrios Karapiperis, Christos Tjortjis, Vassilios S. Verykios
Proc. VLDB Endow.3
2022 Frequent itemset hiding revisited: pushing hiding constraints into mining
Vassilios S. Verykios, Elias C. Stavropoulos, Panteleimon Krasadakis, Evangelos Sakkopoulos
Appl. Intell.1
2021 MultiBlock: A Scalable Iterative Approach for Progressive Entity Resolution
abstract
Progressive entity resolution techniques aim to allow linking vast amounts of records, coming from disparate data sources, in a way that provides early access to linkage results of high recall. However, existing methods suffer from serious limitations, as they either assume a nearly uniform distribution of record pairs in each block, or they use a sorted neighborhood approach which incurs a significant d elay i n t he r eporting of linkage results and can miss matching record pairs.In response, in this paper we introduce MULTIBLOCK, a progressive multi-iterative method that breaks down the matching step of entity resolution into a number of iterations, generating as many matching record pairs as possible upfront, to quickly resolve each block regardless of its size. MULTIBLOCK guarantees the formulation of each record pair with a fixed probability, and iteratively provides accurate estimates of the proportion of matching record pairs. It has linear complexity with the number of blocks and no dependence on the records of the data sets, which is important in large-scale settings. Additionally, MULTIBLOCK can adapt to any progressive algorithm that generates blocks of arbitrary sizes. Through experimental evaluation, using three real-world data sets consisting of millions of record pairs, we show that our approach outperforms four state-of-the-art methods in both accuracy and efficiency, b eing a t l east twice faster than its competitors.
Dimitrios Karapiperis, Aris Gkoulalas-Divanis, Vassilios S. Verykios
IEEE BigData3
2021 Resolving Infeasibility in Linear Programs for the Frequent Itemset Hiding Problem
abstract
Hiding sensitive knowledge in transactional databases is a problem that can be addressed through the use of frequent itemset hiding. A well established and robust methodology for hiding sensitive itemsets in transactional databases is embodied through different database extension schemes. Having considered this field extensively in our past and recent research agenda, we proposed a constraint-based hiding model that relies on Border revision and Linear Programming. The Linear Program strives to find the optimal solution to our problem by suggesting which itemsets to add in the extended database for maximum security and data quality. Unfortunately, linear programs do not always have either feasible or optimal solutions, so in this paper we propose some alternate approaches in case of not feasible Linear Programs and suggest the most suitable ones, depending on the needs of the user.
Panteleimon Krasadakis, Vassilios S. Verykios, Evangelos Sakkopoulos
ICTAI2
2021 Summarizing and linking electronic health records
Dimitrios Karapiperis, Aris Gkoulalas-Divanis, Vassilios S. Verykios
Distributed Parallel Databases3
2020 Efficient Record Linkage in Data Streams
abstract
Nowadays, a vast amount of information is collected in real-time on a daily basis via users' handheld devices, web-based applications, and customer service interactions (among many others). The sheer volume of this data and the unprecedented rate at which it becomes available for processing, potentially combined with other attributes that are commonly met in traditional data sets, calls for novel online record linkage1techniques that can handle streams of data to discover records that refer to the same real-world entity.This paper introduces UniBlock, an online record linkage approach, supported by a novel data structure, that can adapt to any blocking algorithm to separate the most frequently accessed blocks from the rest, and maintain these blocks in main memory. In UniBlock, this separation is performed in a randomized way, where the probability of eviction of a block is inversely proportional to its frequency of access, empowering our approach with simplicity and effectiveness. Additionally, UniBlock provides accurate estimations of the proportion of matching record pairs in the underlying data sets in sublinear running time. Through experimental evaluation, we show that our approach outperforms the state-of-the-art methods in both accuracy and efficiency, being able to scale well to data streams.
Dimitrios Karapiperis, Aris Gkoulalas-Divanis, Vassilios S. Verykios
IEEE BigData3
2020 Parallel based Hiding of Sensitive Knowledge
abstract
Nowadays, privacy preserving data mining is an increasingly popular field of data mining research. frequent itemset-based approaches comprise a large category of techniques where the hiding is exemplified through the Apriori algorithm. This paper extends the work on a previously presented hiding scheme that sanitizes the input database by extending it based on the ideal positive border that is computed through the application of a constraint-based frequent itemset mining algorithm. The goal of the proposed approach is to improve at large on computational aspects of the hiding methodology, and in particular to accommodate bigger datasets by customizing the hiding scheme and allowing it to run in parallel while ensuring the hiding of the sensitive knowledge in its entirety. The proposed approach is a significant acceleration factor provided to business user directly in the form of Software as a Service.
Panteleimon Krasadakis, Vassilios S. Verykios, Evangelos Sakkopoulos
ICTAI2
2019 From Analytics to Cognition: Expanding the Reach of Data in Learning
abstract
Education constitutes a rapidly changing and challenging environment, therefore, a shift from reporting to actionable interventions based on data is almost imperative. At the same time, Learning Analytics is incorporating increasingly advanced tools and methods. Artificial Intelligence and cognitive science allow us to study in depth the behavior of students, creating patterns and prediction models. All the above summarize the scope of the newly established Big Data Analytics and Anonymization Laboratory (BAT Lab) in the Hellenic Open University. This paper presents the vision and the work in progress of the BAT Lab in an attempt not only to produce interpretable results but also to organize and present these results in a highly usable way for non-experts. Additionally, PRIME-EDU software, which is the team’s latest work, is presented.
Rozita Tsoni, Christos Samaras, Evgenia Paxinou, Christos T. Panagiotakopoulos, Vassilios S. Verykios
CSEDU (2)5
2018 Summarization Algorithms for Record Linkage
Dimitrios Karapiperis, Aris Gkoulalas-Divanis, Vassilios S. Verykios
EDBT3
2018 Fast schemes for online record linkage
Dimitrios Karapiperis, Aris Gkoulalas-Divanis, Vassilios S. Verykios
Data Min. Knowl. Discov.3
2018 FEDERAL: A Framework for Distance-Aware Privacy-Preserving Record Linkage
abstract
In privacy-preserving record linkage, a number of data custodians encode their records and submit them to a trusted third-party who is responsible for identifying those records that refer to the same real-world entity. In this paper, we propose FEDERAL, a novel record linkage framework that implements methods for anonymizing both string and numerical data values, which are typically present in data records. These methods rely on a strong theoretical foundation for rigorously specifying the dimensionality of the anonymization space, into which the original values are embedded, to provide accuracy and privacy guarantees under various models of privacy attacks. A key component of the applied embedding process is the threshold that is required by the distance computations, which we prove can be formally specified to guarantee accurate results. We evaluate our framework using three real-world data sets with varying characteristics. Our experimental findings show that FEDERAL offers a complete and effective solution for accurately identifying matching anonymized record pairs (with recall rates constantly above 93 percent) in large-scale privacy-preserving record linkage tasks.
Dimitrios Karapiperis, Aris Gkoulalas-Divanis, Vassilios S. Verykios
IEEE Trans. Knowl. Data Eng.3
2017 Distance-Aware Encoding of Numerical Values for Privacy-Preserving Record Linkage
abstract
In this work, we propose Bit Vectors (BV), an accurate, distance-preserving encoding scheme for representing numerical data values in privacy-preserving tasks. Although many methods have been proposed in the literature for encoding strings, the problem of encoding numerical values has not been effectively addressed yet. In Privacy-Preserving Record Linkage (PPRL), a number of data custodians encode their records and submit them to a trusted third-party that is responsible to identify those records that refer to the same real-world entity. BV is supported by a strong theoretical foundation for embedding numerical values into an anonymization space in a way that preserves the initial distances. Key components of this embedding process are (a) the employed hash functions which, by utilizing random intervals, they allow for approximate matching, and (b) the threshold that is required by the distance computations, which we prove that can be specified in a way that guarantees accurate results.
Dimitrios Karapiperis, Aris Gkoulalas-Divanis, Vassilios S. Verykios
ICDE3
2016 Data Set Operations to Hide Decision Tree Rules
abstract
This paper focuses on preserving the privacy of sensitive patterns when inducing decision trees. Our record augmentation approach for hiding sensitive classification rules in binary datasets is preferred over other heuristic solutions like output perturbation or cryptographic techniques since the raw data itself is readily available for public use. We describe the process and an indicative experiment using a prototype hiding tool.
Dimitrios Kalles, Vassilios S. Verykios, Georgios Feretzakis, Athanassios Papagelis
ECAI2
2016 Efficient Record Linkage Using a Compact Hamming Space
abstract
Record linkage, the process of identifying similar records that correspond to the same real-world entities across databases, is a well-established research problem in the database, data mining, and information retrieval communities. Computing distances between string values of records is the key component in order to determine the similarity of the represented entities. Due to the typically large volumes of records, a two-step process is followed. A blocking mechanism is first applied for grouping similar records together, and then a matching mechanism is performed for comparing the records which have been inserted into the same block. However, there does not exist any efficient blocking/matching mechanism which provides theoretical guarantees for identifying similar records which consist of strings. Towards this end, we put forth the novel notion of embedding string-based records into a Hamming space, where such a mechanism exists. The size of these embeddings is kept as small as needed in order to guarantee the correspondence of distances in that space to the types of errors that exist between strings, e.g., a missing or a modified character. We build embeddings whose size is 120 bits for representing accurately four fields of a publicly available data set. We also present a distance threshold-aware blocking technique for higher accuracy rates compared to blocking approaches which ignore the specified threshold. Our empirical study conducted on real-world data sets shows the efficacy achieved by our embedding method as compared to several existing solutions.
Dimitrios Karapiperis, Dinusha Vatsalan, Vassilios S. Verykios, Peter Christen
EDBT3
2016 Hashing-Based Distributed Multi-party Blocking for Privacy-Preserving Record Linkage
Thilina Ranbaduge, Dinusha Vatsalan, Peter Christen, Vassilios S. Verykios
PAKDD (2)4
2016 A fast and efficient Hamming LSH-based scheme for accurate linkage
Dimitrios Karapiperis, Vassilios S. Verykios
Knowl. Inf. Syst.2
2016 A transversal hypergraph approach for the frequent itemset hiding problem
Elias C. Stavropoulos, Vassilios S. Verykios, Vasileios Kagklis
Knowl. Inf. Syst.2
2015 An Adaptive Web Tool for Self-assessment using Lightweight User Profiles
abstract
This paper presents an adaptive tool for self-assessments. The proposed system supports the selection of assessment items from an item bank based on a number of criteria such as the topic, the difficulty level of the items and a lightweight learner profile. For interoperability reasons, the assessment items are encoded using the IMS QTI standard and the topics are represented in Topic Maps XML. Items are included in the Topic Map as occurrences in one or more subtopics. The items are retrieved using parameterized XQuery scripts and they are adaptively presented to the user based on their knowledge level. Furthermore, some visual clues are associated to the items in the test that participants should attempt. The evaluation experiments showed that the tool supports more effectively self-assessment and motivates users to be more actively engaged.
Fotis Lazarinis, Vassilios S. Verykios, Christos T. Panagiotakopoulos
CSEDU (2)2
2015 Large-Scale Multi-party Counting Set Intersection Using a Space Efficient Global Synopsis
Dimitrios Karapiperis, Dinusha Vatsalan, Vassilios S. Verykios, Peter Christen
DASFAA (2)3
2015 Scalable Blocking for Privacy Preserving Record Linkage
abstract
When dealing with sensitive and personal user data, the process of record linkage raises privacy issues. Thus, privacy preserving record linkage has emerged with the goal of identifying matching records across multiple data sources while preserving the privacy of the individuals they describe. The task is very resource demanding, considering the abundance of available data, which, in addition, are often dirty. Blocking techniques are deployed prior to matching to prune out unlikely to match candidate records so as to reduce processing time. However, when scaling to large datasets, such methods often result in quality loss. To this end, we propose Multi-Sampling Transitive Closure for Encrypted Fields (MS-TCEF), a novel privacy preserving blocking technique based on the use of reference sets. Our new method effectively prunes records based on redundant assignments to blocks, providing better fault-tolerance and maintaining result quality while scaling linearly with respect to the dataset size. We provide a theoretical analysis on the method's complexity and show how it outperforms state-of-the-art privacy preserving blocking techniques with respect to both recall and processing cost.
Alexandros Karakasidis 0001, Georgia Koloniari, Vassilios S. Verykios
KDD3
2015 Privacy Preserving Blocking and Meta-Blocking
Alexandros Karakasidis 0001, Georgia Koloniari, Vassilios S. Verykios
ECML/PKDD (3)3
2015 An LSH-Based Blocking Approach with a Homomorphic Matching Technique for Privacy-Preserving Record Linkage
abstract
We present a Λ-fold Redundant Blocking Framework, that relies on the Locality-Sensitive Hashing technique for identifying candidate record pairs, which have undergone an anonymization transformation. In this context, we demonstrate the usage and evaluate the performance of a variety of families of hash functions used for blocking. We illustrate that the performance attained is highly correlated to the distance-preserving properties of the anonymization format used. The parameters, of the blocking scheme, are optimally selected so that we achieve the highest possible accuracy in the least possible running time. We also introduce an SMC-based protocol in order to compare the formulated record pairs homomorphically, without running the risk of breaching the privacy of the underlying records.
Dimitrios Karapiperis, Vassilios S. Verykios
IEEE Trans. Knowl. Data Eng.2
2014 An Integer Linear Programming Scheme to Sanitize Sensitive Frequent Itemsets
abstract
In this paper, we propose a novel approach to address the frequent item set hiding problem, by formulating it as an integer linear program (ILP). The solution of the ILP points out the transactions that need to be sanitized in order to achieve the hiding of the sensitive frequent item sets, while the impact on other non-sensitive item sets is minimized. We present a novel heuristic approach to calculate the coefficients of the objective function of the ILP, while at the same time we minimize the side effects introduced by the hiding process. We also propose a sanitization algorithm that performs the hiding on the selected transactions. Finally, we evaluate the proposed method on real datasets and we compare the results of the newly proposed method with those of other state of the art approaches.
Vasileios Kagklis, Vassilios S. Verykios, Giannis Tzimas, Athanasios K. Tsakalidis
ICTAI2
2014 Towards Secure and Practical Location Privacy through Private Equality Testing
Emmanouil Magkos, Panayiotis Kotzanikolaou, Marios Magioladitis, Spyros Sioutas, Vassilios S. Verykios
Privacy in Statistical Databases5
2013 Efficient two-party private blocking based on sorted nearest neighborhood clustering
abstract
Integrating data from diverse sources with the aim to identify similar records that refer to the same real-world entities without compromising privacy of these entities is an emerging research problem in various domains. This problem is known as privacy-preserving record linkage (PPRL). Scalability of PPRL is a main challenge due to growing data size in real-world applications. Private blocking techniques have been used in PPRL to address this challenge by reducing the number of record pair comparisons that need to be conducted. Many of these private blocking techniques require a trusted third party to perform the blocking. One main threat with three-party solutions is the collusion between parties to identify the private data of another party.
Dinusha Vatsalan, Peter Christen, Vassilios S. Verykios
CIKM3
2013 A Simulator for Privacy Preserving Record Linkage
Alexandros Karakasidis 0001, Vassilios S. Verykios
EANN (2)2
2013 A Novel Mobile Framework for Anonymity Techniques and Services Research
abstract
Positioning capabilities offered in modern mobile devices enable usage of location-based services. Privacy and security is of great importance for related applications. We present a framework that allows conducting research on anonymity techniques in a real-life environment using smartphones. The proposed solution also includes logging mechanisms that facilitate positioning research dataset development in open format. To present the capabilities of the solution, we deliver the concept of K-anonymity to protect mobile users that issue queries to location-based services. Experimental evaluation of the solution includes development of real-life logging dataset using smartphones by volunteers. Different flavours of anonymity algorithms are easy to be included and tested. The solution has received encouraging feedback and successfully assists the researchers of location based services to experiment, validate and develop their techniques in real life environment.
Evangelos Sakkopoulos, Mersini Paschou, Athanasios K. Tsakalidis, Spyros Sioutas, Vassilios S. Verykios
MDM (1)5
2013 A taxonomy of privacy-preserving record linkage techniques
Dinusha Vatsalan, Peter Christen, Vassilios S. Verykios
Inf. Syst.3
2012 A Highly Efficient and Secure Multidimensional Blocking Approach for Private Record Linkage
abstract
Privacy Preserving Record Linkage is the process of securely integrating information without compromising the privacy of the individuals described by these data. While such an effort sounds appealing for both academic and business applications, it is complicated and computationally intensive. In this paper we aspire to provide a solution to this problem by presenting a highly secure mutidimensional Privacy Preserving Blocking approach which is totally distributed and runs independently on each data holder, making it invulnerable to third party attacks. It is based on the idea of using publicly available corpora of data known as reference sets for creating k-anonymous clusters. We analytically prove that our method is secure and provide experimental results which evaluate the increased performance of our method in terms of matching accuracy and execution time.
Alexandros Karakasidis 0001, Vassilios S. Verykios
ICTAI2
2010 Uncertainty for Anonymity and 2-Dimensional Range Query Distortion
Spyros Sioutas, Emmanouil Magkos, Ioannis Karydis, Vassilios S. Verykios
Privacy in Statistical Databases4
2009 PLOT: Privacy in Location Based Services: An Open-Ended Toolbox
abstract
The widespread adoption of location based services (LBSs) coupled with recent advances in location tracking technologies, pose serious concerns to user privacy. As a consequence, privacy preserving approaches have been proposed to protect the location information which is communicated during a request for an LBS. Most existing approaches are centralized as they rely on a trusted server to protect the real location of the user. Although the centralized approaches are commonplace, so far no attempt has been made to integrate them in a unified framework. Such an integration would provide the means for easily implementing and testing new techniques by offering ready-made vanilla system components and allow for both the experimental and analytical evaluation of the implemented techniques.In this paper we propose PLOT, an open-ended toolbox that allows the implementation and the evaluation of privacy-enhancing algorithms for LBSs. PLOT offers a variety of interesting features: (i) it supports both real and synthetic movement data, (ii) it relies on spatial DBMSs to efficiently handle movement data as well as the underlying model of user movement, (iii) it offers tools for mobile data preprocessing, movement reconstruction and segmentation, (iv) it allows the implementation of both network-based and free-terrain solutions to location privacy, (v) it provides the infrastructure for second-chance approaches when the main location privacy approach fails, (vi) it implements strategies for the identification of frequent patterns in user movement, and finally (vii) it offers an extended set of visualization tools that both provide insight on the workings of the implemented solutions and facilitate the qualitative and quantitative evaluation of their behavior.
Aris Gkoulalas-Divanis, Vassilios S. Verykios, Dimitrios Eleftheriou
Mobile Data Management2
2009 Identifying Unsafe Routes for Network-Based Trajectory Privacy
abstract
In this paper, we propose a privacy model that offers trajectory privacy to the requesters of Location-Based Services (LBSs), by utilizing an underlying network of user movement. The privacy model has been implemented as a framework that (i) reconstructs the user movement from a series of independent location updates, (ii) identifies routes where user privacy is at risk, and (iii) anonymizes online user requests for LBSs to protect the requester for as long as the service withstands completion. In order to achieve (iii), we propose two anonymization techniques, the K–present (weak) and the K–frequent (strong) trajectory anonymity, and a second chance approach that takes over when anonymization fails to ensure that the privacy of the user is preserved. To the best of our knowledge, this is the first work to propose a trajectory privacy model that utilizes an underlying network of user movement to offer in an interactive way personalized privacy to online user requests on trajectory data.
Aris Gkoulalas-Divanis, Vassilios S. Verykios, Mohamed F. Mokbel
SDM2
2009 A network aware privacy model for online requests in trajectory data
Aris Gkoulalas-Divanis, Vassilios S. Verykios, Panayiotis Bozanis
Data Knowl. Eng.2
2009 Hiding sensitive knowledge without side effects
Aris Gkoulalas-Divanis, Vassilios S. Verykios
Knowl. Inf. Syst.2
2009 Exact Knowledge Hiding through Database Extension
abstract
In this paper, we propose a novel, exact border-based approach that provides an optimal solution for the hiding of sensitive frequent itemsets by (i) minimally extending the original database by a synthetically generated database part - the database extension, (ii) formulating the creation of the database extension as a constraint satisfaction problem, (iii) mapping the constraint satisfaction problem to an equivalent binary integer programming problem, (iv) exploiting underutilized synthetic transactions to proportionally increase the support of non-sensitive itemsets, (v) minimally relaxing the constraint satisfaction problem to provide an approximate solution close to the optimal one when an ideal solution does not exist, and (vi) by using a partitioning in the universe of the items to increase the efficiency of the proposed hiding algorithm. Extending the original database for sensitive itemset hiding is proved to provide optimal solutions to an extended set of hiding problems compared to previous approaches and to provide solutions of higher quality. Moreover, the application of binary integer programming enables the simultaneous hiding of the sensitive itemsets and thus allows for the identification of globally optimal solutions.
Aris Gkoulalas-Divanis, Vassilios S. Verykios
IEEE Trans. Knowl. Data Eng.2
2008 A Free Terrain Model for Trajectory K-Anonymity
Aris Gkoulalas-Divanis, Vassilios S. Verykios
DEXA2
2008 A Parallelization Framework for Exact Knowledge Hiding in Transactional Databases
Aris Gkoulalas-Divanis, Vassilios S. Verykios
SEC2
2008 A MaxMin approach for hiding frequent itemsets
George V. Moustakides, Vassilios S. Verykios
Data Knowl. Eng.2
2007 A Hybrid Approach to Frequent Itemset Hiding
abstract
In this paper, we propose a novel, exact border-based approach that provides an optimal solution for the hiding of sensitive frequent itemsets by (i) minimally extending the original database by a synthetically generated database part - the database extension, (ii) formulating the creation of the database extension as a constraint satisfaction problem that is solved by using binary integer programming, and (Hi) providing an approximate solution close to the optimal one when an ideal solution does not exist. Extending the original database for sensitive itemset hiding is proved to provide optimal solutions to an extended set of hiding problems compared to previous approaches and to provide solutions of higher quality.
Aris Gkoulalas-Divanis, Vassilios S. Verykios
ICTAI (1)2
2007 Efficient algorithms for distortion and blocking techniques in association rule hiding
Vassilios S. Verykios, Emmanuel D. Pontikakis, Yannis Theodoridis, LiWu Chang
Distributed Parallel Databases1
2007 Duplicate Record Detection: A Survey
abstract
Often, in the real world, entities have two or more representations in databases. Duplicate records do not share a common key and/or they contain errors that make duplicate matching a difficult task. Errors are introduced as the result of transcription errors, incomplete information, lack of standard formats, or any combination of these factors. In this paper, we present a thorough analysis of the literature on duplicate record detection. We cover similarity metrics that are commonly used to detect similar field entries, and we present an extensive set of duplicate detection algorithms that can detect approximately duplicate records in a database. We also cover multiple techniques for improving the efficiency and scalability of approximate duplicate detection algorithms. We conclude with coverage of existing tools and with a brief discussion of the big open problems in the area
Ahmed K. Elmagarmid, Panagiotis G. Ipeirotis, Vassilios S. Verykios
IEEE Trans. Knowl. Data Eng.3
2006 An integer programming approach for frequent itemset hiding
abstract
The rapid growth of transactional data brought, soon enough, into attention the need of its further exploitation. In this paper, we investigate the problem of securing sensitive knowledge from being exposed in patterns extracted during association rule mining. Instead of hiding the produced rules directly, we decide to hide the sensitive frequent itemsets that may lead to the production of these rules. As a first step, we introduce the notion of distance between two databases and a measure for quantifying it. By trying to minimize the distance between the original database and its sanitized version (that can safely be released), we propose a novel, exact algorithm for association rule hiding and evaluate it on real world datasets demonstrating its effectiveness towards solving the problem. Copyright 2006 ACM.
Aris Gkoulalas-Divanis, Vassilios S. Verykios
CIKM2
2004 An Experimental Study of Distortion-Based Techniques for Association Rule Hiding
abstract
Data mining provides the opportunity to extract useful information from large databases. Various techniques have been proposed in this context in order to extract this information in the most efficient way. However efficiency is not our only concern in this study. The security and privacy issues over the extracted knowledge must be seriously considered as well. By taking this into consideration, we study the discovery of association rules in binary data sets and we propose algorithms for selectively hiding sensitive association rules. Association rule hiding is a well researched area in privacy preserving data mining and many algorithms have been proposed to address it. The algorithms that we introduce use a distortion-based technique for hiding the sensitive rules. The hiding process may introduce a number of side effects either by generating rules which were not previously existing (ghost rules) or by eliminating existing non-sensitive rules (lost rules). The proposed algorithms use effective data structures for the representation of the association rules and they strongly rely on the prioritization of the selection of the transactions to choose for falsification (victim transactions) by using weights. In this paper we show that our algorithms perform better than other similar algorithms in this field in eliminating non-sensitive rules without increasing the processing time significantly. These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.
Emmanuel D. Pontikakis, Achilleas A. Tsitsonis, Vassilios S. Verykios
DBSec3
2004 Association Rule Hiding
abstract
Large repositories of data contain sensitive information that must be protected against unauthorized access. The protection of the confidentiality of this information has been a long-term goal for the database security research community and for the government statistical agencies. Recent advances in data mining and machine learning algorithms have increased the disclosure risks that one may encounter when releasing data to outside parties. A key problem, and still not sufficiently investigated, is the need to balance the confidentiality of the disclosed data with the legitimate needs of the data users. Every disclosure limitation method affects, in some way, and modifies true data values and relationships. We investigate confidentiality issues of a broad category of rules, the association rules. In particular, we present three strategies and five algorithms for hiding a group of association rules, which is characterized as sensitive. One rule is characterized as sensitive if its disclosure risk is above a certain privacy threshold. Sometimes, sensitive rules should not be disclosed to the public since, among other things, they may be used for inferring sensitive data, or they may provide business competitors with an advantage. We also perform an evaluation study of the hiding algorithms in order to analyze their time complexity and the impact that they have in the original database.
Vassilios S. Verykios, Ahmed K. Elmagarmid, Elisa Bertino, Yücel Saygin, Elena Dasseni
IEEE Trans. Knowl. Data Eng.1
2003 Improving Data Quality in Practice: A Case Study in the Italian Public Administration
Paolo Missier, Gail Lalk, Vassilios S. Verykios, F. Grillo, T. Lorusso, Paola Angeletti
Distributed Parallel Databases3
2003 A Bayesian decision model for cost optimal record matching
Vassilios S. Verykios, George V. Moustakides, Mohamed G. Elfeky
VLDB J.1
2002 TAILOR: A Record Linkage Tool Box
abstract
Data cleaning is a vital process that ensures the quality of data stored in real-world databases. Data cleaning problems are frequently encountered in many research areas, such as knowledge discovery in databases, data warehousing, system integration and e-services. The process of identifying the record pairs that represent the same entity (duplicate records), commonly known as record linkage, is one of the essential elements of data cleaning. In this paper, we address the record linkage problem by adopting a machine learning approach. Three models are proposed and are analyzed empirically. Since no existing model, including those proposed in this paper, has been proved to be superior, we have developed an interactive record linkage toolbox named TAILOR (backwards acronym for "RecOrd LInkAge Toolbox"). Users of TAILOR can build their own record linkage models by tuning system parameters and by plugging in in-house-developed and public-domain tools. The proposed toolbox serves as a framework for the record linkage process, and is designed in an extensible way to interface with existing and future record linkage models. We have conducted an extensive experimental study to evaluate our proposed models using not only synthetic but also real data. The results show that the proposed machine-learning record linkage models outperform the existing ones both in accuracy and in performance.
Mohamed G. Elfeky, Ahmed K. Elmagarmid, Vassilios S. Verykios
ICDE3
2002 MyPYTHIA: a recommendation portal for scientific software and services
abstract
Abstract We outline the design of a recommendation system (MyPYTHIA) implemented as a Web portal. MyPYTHIA's design objectives include evaluating the quality and performance of scientific software on Grid platforms, creating knowledge about which software and computational services should be selected for solving particular problems, selecting parameters of software (or of computational services) based on user‐specified computational objectives, providing access to performance data and knowledge bases over the Web and enabling recommendations for targeted application domains. MyPYTHIA uses a combination of statistical analysis, pattern extraction techniques and a database of software performance to map feature‐based representations of problem instances to appropriate software. MyPYTHIA's open architecture allows the user to customize it for conducting individual case studies. We describe the architecture as well as several scientific domains of knowledge enabled by such case studies. Copyright © 2002 John Wiley & Sons, Ltd.
Elias N. Houstis, Ann Christine Catlin, Nitesh Dhanjani, John R. Rice, Naren Ramakrishnan, Vassilios S. Verykios
Concurr. Comput. Pract. Exp.6
2001 Automating the analysis of option pricing algorithms through intelligent knowledge acquisition approaches
abstract
The traditional approach for estimating the performance of numerical methods is to combine an operation's count with an asymptotic error analysis. This analytic approach gives a general feel of the comparative efficiency of methods, but it rarely leads to very precise results. It is now recognized that accurate performance evaluation can be made only with actual measurements on working software. Given that such an approach requires an enormous amount of performance data related to actual measurements, the development of novel approaches and systems that intelligently and efficiently analyze these data is of great importance to scientists and engineers. The paper presents intelligent knowledge acquisition approaches and an integrated prototype system, which enables the automatic and systematic analysis of performance data. The system analyzes the performance data which is usually stored in a database with statistical, and inductive learning techniques and generates knowledge which can be incorporated in a knowledge base incrementally. We demonstrate the use of the system in the context of a case study, covering the analysis of numerical algorithms for the pricing of American vanilla options in a Black and Scholes modeling framework. We also present a qualitative and quantitative comparison of two techniques used for the automated knowledge acquisition phase.
Vassilios S. Verykios, Elias N. Houstis, Lefteri H. Tsoukalas, Konstantinos N. Pantazopoulos
IEEE Trans. Syst. Man Cybern. Part A1
2000 Automating the approximate record-matching process
Vassilios S. Verykios, Ahmed K. Elmagarmid, Elias N. Houstis
Inf. Sci.1
2000 PYTHIA-II: a knowledge/database system for managing performance data and recommending scientific software
abstract
Often scientists need to locate appropriate software for their problems and then select from among many alternatives. We have previously proposed an approach for dealing with this task by processing performance data of the targeted software. This approach has been tested using a customized implementation referred to as PYTHIA. This experience made us realize the complexity of the algorithmic discovery of knowledge from performance data and of the management of these data together with the discovered knowledge. To address this issue, we created PYTHIA-II—a modular framework and system which combines a general knowledge discovery in databases (KDD) methodology and recommender system technologies to provide advice about scientific software/hardware artifacts. The functionality and effectiveness of the system is demonstrated for two existing performance studies using sets of software for solving partial differential equations. From the end-user perspective, PYTHIA-II allows users to specify the problem to be solved and their computational objectives. In turn, PYTHIA-II (i) selects the software available for the user's problem (ii) suggests parameter values, and (iii) assesses the recommendation provided. PYTHIA-II provides all the necessary facilities to set up database schemas for testing suites and associated performance data in order to test sets of software. Moreover, it allows easy interfacing of alternative data mining and recommendation facilities. PYTHIA-II is an open-ended system implemented on public domain software and has been used for performance evaluation in several different problem domains.
Elias N. Houstis, Ann Christine Catlin, John R. Rice, Vassilios S. Verykios, Naren Ramakrishnan, Catherine E. Houstis
ACM Trans. Math. Softw.4
1998 A knowledge based system for evaluation of option pricing algorithms
abstract
Presents the design and prototype implementation of a system built around the FINANZIA system that aims in the automated analysis and classification of option pricing algorithms based on experimental data. The main objective is to assist in the generation, storage and evaluation of large amounts of experimental option pricing data and to facilitate the identification of performance properties of the pricing algorithms with respect to the various problems. The analysis of the data is achieved using statistical and inductive logic techniques and the identified properties are used to expand the knowledge base. We demonstrate the use of the system in the context of a case study covering the pricing of American vanilla options in a Black & Scholes (1973) modeling framework.
Konstantinos N. Pantazopoulos, Vassilios S. Verykios, Elias N. Houstis
CIFEr2
1994 BIND: A Biomedical INteroperable Database System
Catherine E. Houstis, Theodore S. Papatheodorou, Vassilios S. Verykios, Aris Floratos, Ahmed K. Elmagarmid
DEXA3