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In the frame of the series of Invited Talks organised by SKEL | The AI Lab, the Institute will host Dr. Theofilos Mailis, Post Doc. Researcher at the Management of Data, Information & Knowledge Group (MaDgIK), to deliver a talk with the title View selection over knowledge graphs in triple stores. 

The talk will take place in at the Aegeo Meeting Room of the Institute of Informatics & Telecommunications, on Tuesday 14 November at 14:00, Athens time.

About the talk: Knowledge Graphs (KGs) are collections of interconnected and annotated entities that have become powerful assets for data integration, search enhancement, and other industrial applications. Knowledge Graphs such as DBPEDIA may contain billion of triple relations and are intensively queried with millions of queries per day. A prominent approach to enhance query answering on Knowledge Graph databases is View Materialization, ie., the materialization of an appropriate set of computations that will improve query performance.

We study the problem of view materialization and propose a view selection methodology for processing query workloads with more than a million queries. Our approach heavily relies on subgraph pattern mining techniques that allow to create efficient summarizations of massive query workloads while also identifying the candidate views for materialization. In the core of our work is the correspondence between the view selection problem to that of Maximizing a Nondecreasing Submodular Set Function Subject to a Knapsack Constraint. The latter leads to a tractable view-selection process that allows a (1 – e—1)-approximation of the optimal selection of views. Our experimental evaluation shows that all the steps of the view-selection process are completed in a few minutes, while the corresponding rewritings accelerate 67.68% of the queries in the DBPEDIA query workload. Those queries are executed in 2.19% of their initial time on average.

Speaker Bio: Dr. Theophilos Mailis received his Diploma in Electrical Engineering and Computer Engineering from the National Technical University of Athens in 2004. In 2012, he obtained a Ph.D. in Engineering from the Laboratory of Digital Image, Video, and Multimedia of the School of Electrical and Computer Engineering at the National Technical University of Athens, under the supervision of Professor Stefanos Kollias. He has extensive experience as a researcher and programmer in European, Greek, and German research programs. Specifically, after completing his Ph.D., he worked as a postdoctoral researcher in the Computational Logic Group at the Technical University of Dresden in collaboration with Professor Franz Baader. Since 2014, he has been working in the ‘Management of Data, Information, and Knowledge’ (MaDgIK) group of the Department of Informatics and Telecommunications at the National and Kapodistrian University of Athens, collaborating with Professor Giannis Ioannidis. His research interests focus on description logics, knowledge graphs, query optimization techniques, and continuous query answering.

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