Séminaire Donnees et APprentissage Artificiel
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Exploring the Trade-Offs of Web Interfaces to Support Live Queries over (Semantic) Web Data
Intervenant(s) : Olaf Hartig (IDA (Linköping University))In the context of the Linked Open Data effort, a significant number of public SPARQL endpoints had been made available on the Web to provide query-based access to various types of datasets. Many such endpoints have sacrificed high availability because maintaining a server that provides a reliable SPARQL endpoint is costly. To address this issue we have started investigating approaches that shift some of the effort of executing queries from the server to the clients; these approaches rely only on data access interfaces that are limited to simple types of requests. In this two-parts talk I will first introduce two such interfaces and present experimental results that highlight their respective properties. Thereafter, in the second part of the talk, I will introduce an abstract machine model that allows us to study such client-server scenarios formally. I will present results of such a study based on which we have drawn a fairly complete expressiveness lattice that shows the interplay between several combinations of client and server capabilities. Additionally, I will show the usefulness of our model to formally analyze the fine-grain interplay between several metrics such as the number of requests sent to the server, and the bandwidth of communication between client and server.
Olaf is an Assistant Professor at the Department of Computer and Information Science of Linköping University. He holds a Ph.D. in Computer Science from the Humboldt-Universität zu Berlin, and worked previously as a postdoctoral research fellow at the Cheriton School of Computer Science at the University of Waterloo and, thereafter, at the Hasso Plattner Institute, Potsdam. Olaf is interested in problems related to the management of data and databases. His focus in this broad context is on data on the Web and on graph data, as well as on problems in which the data is distributed over multiple, autonomous and/or heterogeneous sources. Regarding these topics, Olaf's interests range from systems-building related research (e.g., efficient storage of data, query processing, and query optimization) all the way to theoretical foundations (e.g., complexity and expressive power of query languages). Olaf was honored with the SWSA Distinguished Dissertation Award in 2015 for his Ph.D. dissertation “Querying a Web of Linked Data: Foundations and Query Execution,” and he has received two best research paper awards (ESWC 2009 and ESWC 2015). Olaf is leader or contributor of several open source projects, most notably SQUIN, which is a novel query processing system for the Semantic Web. He co-organized international research workshops, served on multiple program committees, and participated as an invited expert in the provenance incubator group and the provenance working group of the World Wide Web Consortium.
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