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The Problem of Correlation and Substitution in SPARQL -- Extended Version [article]

Daniel Hernández and Claudio Gutierrez and Renzo Angles
2018 arXiv   pre-print
We show that at the core of this problem lies the historically troubling notion of logical substitution.  ...  In this paper we study why different implementations of SPARQL (Fuseki, Virtuoso, Blazegraph and rdf4j) behave differently when evaluating queries with correlated variables.  ...  Of course the example is highly unnatural but, as we will show, it codes the essence of the problems of substitution of correlated variables in SPARQL.  ... 
arXiv:1801.04387v2 fatcat:yxjpcs7ksve4fn724myw2grxx4

Cost-Driven Ontology-Based Data Access (Extended Version) [article]

Davide Lanti, Guohui Xiao, Diego Calvanese
2018 arXiv   pre-print
In this work, we show that translating to UCQs is not always the best choice, and that, under certain conditions on the interplay between the ontology, the map- pings, and the statistics of the data, alternative  ...  Standard translation techniques in OBDA try to transform the user query into a union of conjunctive queries (UCQ), following the heuristic argument that UCQs can be efficiently evaluated by modern relational  ...  Conclusion and Future Work In this paper, we have studied the problem of finding efficient alternative translations of a user query in OBDA.  ... 
arXiv:1707.06974v2 fatcat:kptqhkvfv5bgvetibkyw6tqooq

Revealing Secrets in SPARQL Session Level [article]

Xinyue Zhang, Meng Wang, Muhammad Saleem, Axel-Cyrille Ngonga Ngomo, Guilin Qi, Haofen Wang
2020 arXiv   pre-print
, approximation, and relaxation techniques in the future.  ...  In particular, we thoroughly assess query changes made by users w.r.t. structural and data-driven features of SPARQL queries.  ...  (version 2, 15 from Bio2RDF [4] and 3 oth- ers), containing real-world SPARQL queries collected from public SPARQL end- points of these datasets.  ... 
arXiv:2009.06625v2 fatcat:kjuwevbkpvckbblcqcwnllra6y

Extending SPARQL Algebra to Support Efficient Evaluation of Top-K SPARQL Queries [chapter]

Alessandro Bozzon, Emanuele Della Valle, Sara Magliacane
2012 Lecture Notes in Computer Science  
Top-k queries can be expressed in SPARQL by appending to a SELECT query the ORDER BY and LIMIT clauses, which impose a sorting order on the result set, and limit the number of results.  ...  In this paper, we present SPARQL-RANK, an extension of the SPARQL algebra and execution model that supports ranking as a first-class SPAR-QL construct.  ...  We also run some preliminary experiments using our prototype on an extended version of the BSBM.  ... 
doi:10.1007/978-3-642-34213-4_10 fatcat:l4v2yejsvnavfmljimpb2ovsja

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  ...  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.  ...  The basis of the query language is the DIACHRON graph pattern, which, in the context of extending SPARQL, is a specialization of a SPARQL graph pattern, thus making SPARQL queries valid DIACHRON QL queries  ... 
arXiv:1504.01891v3 fatcat:wazigr2bsnamve3wpo2avfnzq4

Certain Answers for SPARQL with Blank Nodes [chapter]

Daniel Hernández, Claudio Gutierrez, Aidan Hogan
2018 Lecture Notes in Computer Science  
A prominent example of such usage can be found in the Wikidata dataset where, e.g., the author of Beowulf is given as a blank node.  ...  We thus explore the feasibility of an alternative SPARQL semantics based on certain answers.  ...  Acknowledgements The work was also supported by the Millennium Institute for Foundational Research on Data (IMFD) and by Fondecyt Grant No. 1181896.  ... 
doi:10.1007/978-3-030-00671-6_20 fatcat:imtlfngijzaqtj2fml6cmno6ay

SPBERT: An Efficient Pre-training BERT on SPARQL Queries for Question Answering over Knowledge Graphs [article]

Hieu Tran, Long Phan, James Anibal, Binh T. Nguyen, Truong-Son Nguyen
2021 arXiv   pre-print
By incorporating masked language modeling objectives and the word structural objective, SPBERT can learn general-purpose representations in both natural language and SPARQL query language.  ...  The experimental results show that SPBERT can obtain promising results, achieving state-of-the-art BLEU scores on several of these tasks.  ...  To alleviate the out-of-vocabulary problem in tokenization, we use WordPiece [17] to split the query sentence into subword units.  ... 
arXiv:2106.09997v2 fatcat:6k2ids2m4faglbj5nmrmwiqliu

Negation in SPARQL [article]

Renzo Angles, Claudio Gutierrez
2016 arXiv   pre-print
This paper presents a thorough study of negation in SPARQL. The types of negation supported in SPARQL are identified and their main features discussed.  ...  Then, we study the expressive power of the corresponding negation operators. At this point, we identify a core SPARQL algebra which could be used instead of the W3C SPARQL algebra.  ...  We will show, for each axiom, examples of cases not satisfied by the negation operators. We will use a generic operator NEG to denote any of the operators used in our analysis, i.e. DIFF and MINUS.  ... 
arXiv:1603.06053v4 fatcat:exwwk76havflldeft5ew6dbpvy

Heuristics-based query optimisation for SPARQL

Petros Tsialiamanis, Lefteris Sidirourgos, Irini Fundulaki, Vassilis Christophides, Peter Boncz
2012 Proceedings of the 15th International Conference on Extending Database Technology - EDBT '12  
For this, we define the variable graph and we show a reduction of the SPARQL query optimization problem to the maximum weight independent set problem.  ...  We present these in the context of a new Heuristic SPARQL Planner (HSP) that is capable of exploiting the syntactic and the structural variations of the triple patterns in a SPARQL query in order to choose  ...  We used MonetDB5 11.2.0 [20] and RDF-3X version 0.3.5. MonetDB was extended with the Redland Raptor 1.9.0 [28] parser to parse the RDF triples and store them as regular tables in MonetDB.  ... 
doi:10.1145/2247596.2247635 dblp:conf/edbt/TsialiamanisSFCB12 fatcat:onpf27gmvndabivryphmeczcse

Mind the Cultural Gap: Bridging Language-Specific DBpedia Chapters for Question Answering [chapter]

Elena Cabrio, Julien Cojan, Fabien Gandon
2014 Towards the Multilingual Semantic Web  
In the current version of QAKiS, English, French and German DBpedia chapters are queried using a natural language interface.  ...  In this chapter we first propose an approach to automatically extend the existing alignments, and we then present an extension of QAKiS, a system for Question Answering over Linked Data that allows to  ...  topic, we are investigating the problem of reconciling information obtained by distributed SPARQL endpoints.  ... 
doi:10.1007/978-3-662-43585-4_9 fatcat:ettfisn7hre5rfxqa5untxa6ei

FedX: Optimization Techniques for Federated Query Processing on Linked Data [chapter]

Andreas Schwarte, Peter Haase, Katja Hose, Ralf Schenkel, Michael Schmidt
2011 Lecture Notes in Computer Science  
In experiments, we demonstrate the practicability and efficiency of our framework on a set of real-world queries and data sources from the Linked Open Data cloud.  ...  We propose novel join processing and grouping techniques to minimize the number of remote requests, and develop an effective solution for source selection in the absence of preprocessed metadata.  ...  Research reported in this paper was partially supported by the German BMBF in the project CollabCloud.  ... 
doi:10.1007/978-3-642-25073-6_38 fatcat:3mgfop65s5dmbpmkterq4j2hve

Using AberOWL for fast and scalable reasoning over BioPortal ontologies

Luke Slater, Georgios V. Gkoutos, Paul N. Schofield, Robert Hoehndorf
2016 Journal of Biomedical Semantics  
Acknowledgements This paper is an extended version of a conference paper by the same name, presented at ICBO 2015.  ...  The time required to answer a query using AberOWL correlates linearly with the number of logical axioms in the ontologies (Pearson correlation, ρ = 0.33), and also strongly correlates with the number of  ...  We extended the AberOWL framework to obtain a list of ontologies from the Bioportal repository, periodically checking for new ontologies as well as for new versions of existing ontologies.  ... 
doi:10.1186/s13326-016-0090-0 pmid:27502585 pmcid:PMC4976511 fatcat:nxvmvxi6evbo5dk3amtqmfvc2u

SPARQL1.1: New Features and Friends (OWL2, RIF) [chapter]

Axel Polleres
2010 Lecture Notes in Computer Science  
the data" to express incomplete information, written as _:x or [] Literals, e.g. "2010"^^xsd:gYear "Brixen"@de "Bressanone"@it "Diego Calvanese"  ...  URIs, e.g. Blanknodes: "existential variables in  ...  identified as both desirable and important for interoperability based on experience with the initial version of the standard  ... 
doi:10.1007/978-3-642-15918-3_3 fatcat:vbtjrsucvnhcnoj7o3j45pzlhy

Mining Software Repositories with iSPAROL and a Software Evolution Ontology

Christoph Kiefer, Abraham Bernstein, Jonas Tappolet
2007 Fourth International Workshop on Mining Software Repositories (MSR'07:ICSE Workshops 2007)  
Together with EvoOnt, iSPARQL can accomplish a sizable number of tasks sought in software repository mining projects, such as an assessment of the amount of change between versions or the detection of  ...  Since OWL describes the semantics of the data, EvoOnt is (1) easily extendible, (2) comes with many existing tools, and (3) allows to derive assertions through its inherent Description Logic reasoning  ...  edit operations: insertion, substitution, and deletion of nodes [15] .  ... 
doi:10.1109/msr.2007.21 dblp:conf/msr/KieferBT07 fatcat:2ze7bky6tbbltovifjrcmallza

Benchmarking Knowledge Graphs on the Web [article]

Michael Röder and Mohamed Ahmed Sherif and Muhammad Saleem and Felix Conrads and Axel-Cyrille Ngonga Ngomo
2020 arXiv   pre-print
History in computer science has shown that a main driver to scientific advances, and in fact a core element of the scientific method as a whole, is the provision of benchmarks to make progress measurable  ...  The growing interest in making use of Knowledge Graphs for developing explainable artificial intelligence, there is an increasing need for a comparable and repeatable comparison of the performance of Knowledge  ...  In (Cornolti et al., 2013) , the authors propose a set of different extraction types that can be benchmarked. These definitions are further refined and extended in .  ... 
arXiv:2002.06039v1 fatcat:tc25o6rplbekndjng4cqh2oxoe
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