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Hierarchical Characteristic Set Merging for Optimizing SPARQL Queries in Heterogeneous RDF [article]

Marios Meimaris, George Papastefanatos
2018 arXiv   pre-print
Characteristic sets (CS) organize RDF triples based on the set of properties characterizing their subject nodes. This concept is recently used in indexing techniques, as it can capture the implicit schema of RDF data. While most CS-based approaches yield significant improvements in space and query performance, they fail to perform well in the presence of schema heterogeneity, i.e., when the number of CSs becomes very large, resulting in a highly partitioned data organization. In this paper, we
more » ... In this paper, we address this problem by introducing a novel technique, for merging CSs based on their hierarchical structure. Our technique employs a lattice to capture the hierarchical relationships between CSs, identifies dense CSs and merges dense CSs with their ancestors, thus reducing the size of the CSs as well as the links between them. We implemented our algorithm on top of a relational backbone, where each merged CS is stored in a relational table, and we performed an extensive experimental study to evaluate the performance and impact of merging to the storage and querying of RDF datasets, indicating significant improvements.
arXiv:1809.02345v1 fatcat:6vuyp5oam5ezvhmpfzvybssm2q

Towards a Methodology for Publishing Linked Open Statistical Data

Irene Petrou, Marios Meimaris, George Papastefanatos
2014 JeDEM - eJournal of eDemocracy & Open Government  
Marios Meimaris received his Diploma in Electrical and Computer Engineering from the National Technical University of Athens.  ...  Marios has served as invited expert in W3C's Government Linked Data working group. Center, where he is involved in several R&D EU and national projects.  ... 
doi:10.29379/jedem.v6i1.322 fatcat:qeikub3ldvhnplipktr5voz4nm

Computational methods and optimizations for containment and complementarity in web data cubes

Marios Meimaris, George Papastefanatos, Panos Vassiliadis, Ioannis Anagnostopoulos
2018 Information Systems  
Multidimensional data are published in the web of data under common directives, such as the Resource Description Framework (RDF). The increasing volume and diversity of these data pose the challenge of finding relations between them in a most efficient and accurate way, by taking into advantage their overlapping schemes. In this paper we define two types of relationships between multidimensional RDF data, and we propose algorithms for efficient and scalable computation of these relationships.
more » ... se relationships. Specifically, we define the notions of containment and complementarity between points in multidimensional dataspaces, as different aspects of relatedness, and we propose a baseline method for computing them, as well as two alternative methods that target speed and scalability. We provide an experimental evaluation over real-world and synthetic datasets and we compare our approach to a SPARQL-based and a rule-based alternative, which prove to be inefficient for increasing input sizes.
doi:10.1016/ fatcat:xtzdi5t6fvcnxhzz7czyhs3cxy

LinkZoo: A Linked Data Platform for Collaborative Management of Heterogeneous Resources [chapter]

Marios Meimaris, George Alexiou, George Papastefanatos
2014 Lecture Notes in Computer Science  
Modern collaborations rely on sharing and reusing heterogeneous resources. The ability to combine different types of information objects in semantically meaningful ways becomes a necessity for the information-intensive requirements of collaborative environments. In this paper we present LinkZoo, a web-based, linked data enabled platform that allows users to create, manage, discover and search heterogeneous resources such as files, web documents, people and events, interlink them, annotate them,
more » ... hem, annotate them, exploit their inherent structures, enrich them with semantics and make them available as linked data. LinkZoo easily and intuitively allows for dynamic communities that enable web-based collaboration through resource sharing and annotating, exposing objects on the Linked Data Web under controlled vocabularies and permissions.
doi:10.1007/978-3-319-11955-7_57 fatcat:wge57fhbbfgznkotwqm72yqdje

Public Spending as LOD: The Case of Greece

Michalis N. Vafopoulos, Marios Meimaris, Ioannis Anagnostopoulos, Agis Papantoniou, Ioannis Xidias, Giorgos Alexiou, Giorgos Vafeiadis, Michailis Klonaras, Vasilis Loumos
2013 Social Science Research Network  
The PSGR project is the first attempt to generate, curate, interlink and distribute daily updated public spending data in LOD formats that can be useful to both expert (i.e. scientists and professionals) and naïve users. The PSGR ontology is based on the UK payments ontology and reuses, among others, the W3C Registered Organization Vocabulary and the Core Business Vocabulary. RDFized data are linked to product classifications, Geonames and DBpedia resources. Online services contain advanced
more » ... ontain advanced search features and domain level information (e.g. local government), simple and complex visualizations based on network analysis, linked information about payment entities and SPARQL endpoints. During February 2013, the growing dataset consists of approximately 2 mil. payment decisions valued 44,5 bil. euros forming 65 mil. triples.
doi:10.2139/ssrn.2233998 fatcat:7lurxei5erhp3pqh3hbthni5oi

A Framework for Managing Evolving Information Resources on the Data Web [article]

Marios Meimaris, George Papastefanatos, Christos Pateritsas, Theodora Galani, Yannis Stavrakas
2015 arXiv   pre-print
The web of data has brought forth the need to preserve and sustain evolving information within linked datasets; however, a basic requirement of data preservation is the maintenance of the datasets' structural characteristics as well. As open data are often found using different and/or heterogeneous data models and schemata from one source to another, there is a need to reconcile these mismatches and provide common denominations of interpretation on a multitude of levels, in order to be able to
more » ... rder to be able to preserve and manage the evolution of the generated resources. In this paper, we present a linked data approach for the preservation and archiving of open heterogeneous datasets that evolve through time, at both the structural and the semantic layer. We first propose a set of re-quirements for modelling evolving linked datasets. We then proceed on concep-tualizing a modelling framework for evolving entities and place these in a 2x2 model space that consists of the semantic and the temporal dimensions.
arXiv:1504.06451v2 fatcat:t3dvjwcs3zdpbm6mm7ua4ul7kq

A Query Language for Multi-version Data Web Archives [article]

Marios Meimaris, George Papastefanatos, Stratis Viglas, Yannis Stavrakas, Christos Pateritsas, Ioannis Anagnostopoulos
2016 arXiv   pre-print
The Data Web refers to the vast and rapidly increasing quantity of scientific, corporate, government and crowd-sourced data published in the form of Linked Open Data, which encourages the uniform representation of heterogeneous data items on the web and the creation of links between them. The growing availability of open linked datasets has brought forth significant new challenges regarding their proper preservation and the management of evolving information within them. In this paper, we focus
more » ... his paper, we focus on the evolution and preservation challenges related to publishing and preserving evolving linked data across time. We discuss the main problems regarding their proper modelling and querying and provide a conceptual model and a query language for modelling and retrieving evolving data along with changes affecting them. We present in details the syntax of the query language and demonstrate its functionality over a real-world use case of evolving linked dataset from the biological domain.
arXiv:1504.01891v3 fatcat:wazigr2bsnamve3wpo2avfnzq4

Acknowledgement to Reviewers of Information in 2018

Information Editorial Office
2019 Information  
Marzi, Claudia Mashima, Daisuke Mateos, Cristian Matić, Frano Matsumoto, Ryutaroh Mayo, Michael Mazzeo, Pier Luigi Mcdonald, Scott McGregor, Simon Medvedev, Viktor Meharouech, Amira Meimaris  ...  Maragoudakis, Manolis Marais, Mario Maran, Vinicius Mardani, Abbas Margaris, Dionisis Marian, Romeo Mariani, Ilaria Markakis, Evangelos K. Marston, Hannah R.  ... 
doi:10.3390/info10010023 fatcat:qeundy7bwvhqzkffn4uqrjltmq

Reconsidering the Date of the En-Gedi Leviticus Scroll (EGLev): Exploring the Limitations of the Comparative-Typological Paleographic Method

Drew Longacre
2018 Textus: Annual of the Hebrew University Bible Project  
Politis 33 Meimaris et al., Inscriptions, 64-66, pl. XV.  ...  Meimaris longacre Textus 27 (2018) 44-84 37For a discussion of the large size, see Sirat,Les papyrus, 35-38, 119. 38 W.D.  ... 
doi:10.1163/2589255x-02701004 fatcat:o2fj2ul2pnanra2pvp2oncxvs4

A Hierarchical Aggregation Framework for Efficient Multilevel Visual Exploration and Analysis [article]

Nikos Bikakis, George Papastefanatos, Melina Skourla, Timos Sellis
2016 arXiv   pre-print
Further, we thank Giorgos Giannopoulos and Marios Meimaris for many helpful comments on earlier versions of this article.  ... 
arXiv:1511.04750v4 fatcat:23kschvh2fgydm3n67svnqi3w4

National OSC initiatives models [article]

Eleni Toli, Elli Papadopoulou, Christos Liatas, Electra Sifakaki, Ilias Papastamatiou, Ognjen Prnjat
2020 Zenodo  
., MEIMARIS M., JISC L.M, DANS R.T, (2018). European Open Science Cloud for Research pilot project (EOSCpilot), Deliverable 3.2: EOSC Open Science Monitor specifications, v 1.0.  ...  General for European Programmes  Mandated organisation: To be appointed  Participation in EOSC pillars: OpenAIRE: Sylvia Koukounidou, Natasa Ioannou, Zafeiro Marti all from the University of Cyprus, NGI: Marios  ... 
doi:10.5281/zenodo.4061800 fatcat:nk7spvxzbjhljaem4h4zumfxga

Greek Geopolitical Linked Data: The Case of Public Spending:

Γεώργιος Ηλία Αλεξίου
Of course, this work could never be carried out without the support and the help of the team, which is composed of Marios Meimaris, Agis Papantoniou, Ioannis Xidias, Georgios Vafeiadis  ... 
doi:10.26262/ fatcat:jvkg72mvqfgohjk4dkjefiksxe

Natural Language Processing and Information Extraction

Νικόλαος Ε. Στυλιανού
Michalis Vafopoulos, Marios Meimaris, Agis Papantoniou, Ioannis Anagnostopoulos, Ioannis Xidias, George Alexiou, Giorgos Vafeiadis, and Vassilis Loumos. 2012.  ...  Leon Weber, Mario Sänger, Jannes Münchmeyer, Maryam Habibi, Ulf Leser, and Alan Akbik. 2021. HunFlair: an easy-to-use tool for state-of-the-art biomedical named entity recognition.  ... 
doi:10.26262/ fatcat:xnmddj3t7jg7poadfwrsxqsi6a

Hagia Koryphe (Jabal Musa) in Sinai, Egypt

Georgios Manginis
Jesuit missions aiming to attract Sinai back into contact with Rome (like the one by Mario Amato in 1583) proved fruitless; see Libois 1993 : 63. 804 Gregoriades 1875 Eckenstein 1921: 148-50, 166; Amantos  ...  importantly, they provide concrete evidence from the site itself for the ziyara tradition mentioned in sources since the first Islamic centuiy (section 4 .1).692 pagination, material studied by Dr Ioannis Meimaris  ... 
doi:10.25501/soas.00028729 fatcat:yr3o45rthbbnpcd77gqqxdma3a