Workshop on the Art of Data Structures 2017 17 November, Patras, Greece A Glimpse at Athanasios Tsakalidis Elementary data structures and applications by Assoc. prof. Christos Makris Root & Route • Katerini (1950 – 1968) – Born on 1950 – Childhood, primary & secondary education • Thessaloniki (1968 – 1973) – Undergrad studies and took his Diploma of Mathematics, Aristotle University • Military service (1974-1976) • Saarbrucken, MA (1976 – 1983) – Postgrad studies at University of Saarland . – Master 1981 (Sorting presorted files) – PhD 1982 (Some Results for the Dictionary Problem) Patras 16.09.2015 2 Academic Career Date Position 1983 (Jan) Participating in Projects of DFG (Deutsche Forschungs Gemeinschaft) and teaching the courses: Data Structures, Graph Algorithms, Computational Geometry, • AcA Praxis of programming, in the University of Saarbrucken. 1985 (Sep) Assistant Professor in the Department of Computer Engineering and Informatics of University of Patras. 1988 (summer) Associate Professor in the Department of Computer Engineering and Informatics of University of Patras. 1989-1993 and Vice-Chairman of the department 2007-2009 1992 – 2017 Full Professor at Univ. of Patras 1996 – today R&D-Coordinator of the Research Academic Computer Technology Institute (Patras, Greece) (http://www.cti.gr) 1993-1997, 2001-2005 Chairman, in the Department of Computer Engineering and 2009 – 2013 and Informatics of University of Patras Scientific Career 1999-2002: Member of the Hellenic Supreme Council for Selection of Personnel (Evaluation Committee for specialties related to Computer Science). 1999-2000: Chairman of the Committee enacted by the Hellenic Ministry of the Interior, Public Administration and Decentralization for the Delivery of External Comptrollers Project on the Problem of the year 2000. 2000-2002: Member of the Group of Direct Interference of the Hellenic Republic Ministry of the Interior Public Administration and Decentralization. 2000-2002: Member of the Introductory Committee for the Strategic Design of the Informatics in the Health & Provision. 2001-2004: Member of the Strategic Committee for the Informatics in the Education. 2001-2004: Member of the Committee for the Digital Hellenic Cultural Reserve. 2005-today: Member of the Hellenic Supreme Council for Selection of Personnel (Evaluation Committee for specialties related to Computer Science). December 05- today: Record to the online encyclopedia “WikiPedia – the free Enclyclopedia”, under the category Greek Computer Scientists and the catefory Greek Academics (http://en.wikipedia.org/wiki/Athanasios_Tsakalidis) Research Areas Algorithms & Internet & Multimedia Complexity Applications • Data Structures • Web Engineering • Graph Algorithms • Internet – Intranet Applications • Computational Geometry • Electronic Commerce • Expert Systems • Tele-cooperation • GIS • Distance Learning • Medical Informatics • Tele-medicine • Databases • Electronic Business • Multimedia • Multimedia • Information Retrieval • Data Compression Techniques • Bioinformatics • Digital Image and Video Processing • Video on Demand • Educational Software Patras 16.09.2015 5 Key Features • Identify core problems in elementary data structures Visionary • Explore and combine efficiently techniques & methodologies • Mentoring students • Huge time investment at Inspiring training young scientists Patras 16.09.2015 6 Numbers Publications 480+ Citations 2978+ Books 5 (google scholar) Chapters in books/volumes 26 h-index 27 Journals 112 i10-index 81 Conferences 250 Archived repositories 23 Editor in Journals 1 Diploma theses 599 Masters theses 87 PhDs awarded 29 (12 elected professors) Recommendation letters 2222 (300 of them now university professors) Patras 16.09.2015 7 Achievements (1) https://en.wikipedia.org/wiki/Athanasios_Tsakalidis • He is one of the 48 writers (6 of whom have received the ACM Turing Award) of the ground- laying computer science book, Handbook of Theoretical Computer Science, 1990, Vol A Elsevier Science publishers, co-published by MIT Press, his work being, along with professor Kurt Mehlhorn, in Chapter 6: Data Structures (his favourite field). Achievements (2) https://en.wikipedia.org/wiki/Athanasios_Tsakalidis • His results on the list manipulation and localized search problems in the 1980s led to the foundation of the persistence theory on data structures, developed by Prof. Robert E. Tarjan. • Other significant results on the design and analysis of data structures were contributed on the problems of interpolation search, nearest common ancestor and negative cycle Achievements (3) https://en.wikipedia.org/wiki/Athanasios_Tsakalidis • He is cited and acknowledged by prominent computer scientists like Robert E. Tarjan, Ian J. Munro, Dan Willard, Jon Bentley, Jan van Leeuwen, Timothy M. Chan, Lars Arge, Mihai Patrascu, Erik Demaine, Mikkel Thorup, Prosenjit Bose, Gerth S. Brodal, Haim Kaplan, Peter Widmayer, Giuseppe F. Italiano, Peyman Afshani, Kasper Larsen and more. Research Highlights (influential) Athanasios K. Tsakalidis, Maintaining order in a generalized linked list. Acta Inf. 21: 101-112 (1984) Athanasios K. Tsakalidis, AVL-Trees for Localized Search. Information and Control 67(1-3): 173-194 (1985) Athanasios K. Tsakalidis, The Nearest Common Ancestor in a Dynamic Tree. Acta Inf. 25(1): 37-54 (1988) Kurt Mehlhorn, Athanasios K. Tsakalidis: Dynamic Interpolation Search. J. ACM 40(3): 621-634 (1993) Patras 16.09.2015 11 Maintaining order in a generalized linked list. Result: the proposed structure performs n insertions and deletions in O(n log n) steps and determines the order of two query elements in constant time, assuming that the locations of the queried elements at are given. Used in, implied: James R. Driscoll, Neil Sarnak, Daniel Dominic Sleator, Robert Endre Tarjan: Making Data Structures Persistent. J. Comput. Syst. Sci. 38(1): 86-124 (1989) Stephen Alstrup , Theis Rauhe, Improved labeling scheme for ancestor queries, Proceedings of the thirteenth annual ACM-SIAM symposium on Discrete algorithms, p.947-953, January 06-08, 2002, San Francisco, California Gerth Stølting Brodal , Konstantinos Tsakalidis , Spyros Sioutas , Kostas Tsichlas, Fully persistent B-trees, Proceedings of the Twenty-Third Annual ACM-SIAM Symposium on Discrete Algorithms, p.602-614, January 17-19, 2012, Kyoto, Japan AVL-Trees for Localized Search Result: a data structure based on AVL-trees which allows an insertion or a deletion of an element to be performed in time O(log d), where d is the distance of the position searched for from a finger which points to the end of the file. Moving a finger to a distance d costs O(log d). Used in, implied: James R. Driscoll, Neil Sarnak, Daniel Dominic Sleator, Robert Endre Tarjan: Making Data Structures Persistent. J. Comput. Syst. Sci. 38(1): 86-124 (1989) Haim Kaplan, Robert Endre Tarjan, Purely Functional Representations of Catenable Sorted Lists. STOC 1996: 202-211 Gerth Stølting Brodal: Finger Search Trees with Constant Insertion Time. SODA 1998: 540-549 Gerth Stølting Brodal, George Lagogiannis, Christos Makris, Athanasios K. Tsakalidis, Kostas Tsichlas: Optimal finger search trees in the pointer machine. J. Comput. Syst. Sci. 67(2): 381-418 (2003) The nearest common ancestor in a dynamic tree Result: an implementation of a dynamic tree in a pointer machine is presented which needs linear space, performs m arbitrary insertions and deletions in the initially empty tree in time O(m) and a query about nca(x, y) can be answered on-line in time O(log(min{depth(x), depth(y))+α(k,k))}. Used in, implied: Stephen Alstrup , Jacob Holm, Improved Algorithms for Finding Level Ancestors in Dynamic Trees, Proceedings of the 27th International Colloquium on Automata, Languages and Programming, p.73-84, July 09-15, 2000 Stephen Alstrup, Mikkel Thorup, Optimal Pointer Algorithms for Finding Nearest Common Ancestors in Dynamic Trees. J. Algorithms 35(2): 169-188(2000) Gerth Stølting Brodal, Christos Makris, Spyros Sioutas, Athanasios K. Tsakalidis, Kostas Tsichlas: Optimal Solutions for the Temporal Precedence Problem. Algorithmica 33(4): 494-510 (2002) Dynamic Interpolation Search Result: a data structure called Interpolation Search tree (IST) is presents which supports interpolation search and insertions and deletions. Amortized insertion and deletion cost is O(log n). The expected search time in a random file is O(log log n). This is not only true for the uniform distribution but for a wide class of probability distributions. Used in, implied: Alexis C. Kaporis, Christos Makris, Spyros Sioutas, Athanasios K. Tsakalidis, Kostas Tsichlas, Christos D. Zaroliagis: Improved Bounds for Finger Search on a RAM. Algorithmica 66(2): 249-286 (2013) Alexis C. Kaporis, Christos Makris, George Mavritsakis, Spyros Sioutas, Athanasios K. Tsakalidis, Kostas Tsichlas, Christos D. Zaroliagis: ISB-Tree: A New Indexing Scheme with Efficient Expected Behaviour. ISAAC 2005: 318-327) Alexis C. Kaporis, Christos Makris, Spyros Sioutas, Athanasios K. Tsakalidis, Kostas Tsichlas, Christos D. Zaroliagis: Dynamic Interpolation Search Revisited. ICALP (1) 2006: 382-394 Contents • Optimal Search Trees with fingers in Pointer Machine • Temporal precedence query in PPM (Pure Pointer Machine Model) • Results in string algorithmics Finger Search Trees • ACM STOC 2002 • Journal of Computer and System Sciences, Special Issue devoted to STOC 2002 Finger Search Trees Maintain a sequence of ordered elements supporting the following operations: Insert(f,x) 4 6 8 9 4 6 7 8 9 f x=7