"Next-Generation Experiment Management Systems" , 12th Int’l Conf. on Scientific and Statistical Database Mgnt., Βερολίνο, Γερμανία, Ιούλιος 2000 (keynote talk).

"Databases and the Web: An Oxymoron or a Pleonasm" , 8th Euromicro Wkshp on Parallel & Distributed Processing, Ρόδος, Ελλάδα, Ιανουάριος 2000 (keynote talk).

"Scientific Workflow Management" , 2nd European Conference on Digital Libraries, Ηράκλειο, Ελλάδα, Σεπτέμβριος 1998 (invited talk).

"Desktop Experiment Management" , Johns Hopkins University, Βαλτιμόρη, MD, ΗΠΑ, Νοέμβριος 1994 (Distinguished Lecturer Series).

"Databases and the Web: An Oxymoron or a Pleonasm" , 1st HELDINET Seminar, Αθήνα, Ελλάδα,  Ιούλιος 2000.

"ZOO: A Desktop Experiment Management Environment" ,

	Warner-Lambert Global R&D IT Vision Conference, Maumee, OH, ΗΠΑ, Ιούνιος 1999 (προσκεκλημένη ομιλία).
	AT&T Labs and Bell Labs, Murray Hill, NJ, ΗΠΑ, Νοέμβριος 1996.
	University of Maryland, College Park, MD, ΗΠΑ, Νοέμβριος 1996.
	22nd Int’l VLDB Conference, Bombay, Ινδία, Σεπτέμβριος 1996.
	Indian Institute of Science, Bangalore, Ινδία, Αύγουστος 1996.
	Indian Institute of Technology, New Delhi, Ινδία, Αύγουστος 1996.

"Bitmap Index Design" , CWI and University of Amsterdam, Ολλανδία, Νοέμβριος  1997.

"Histograms" , Data Reduction Workshop, AT&T Labs, ΗΠΑ, Ιούνιος 1997.

"Querying External Scientific Systems" , Workshop on Data Matching and Mapping, Greenbelt, MD, ΗΠΑ, Νοέμβριος 1996.

"Estimation of Query-Result Distribution and its Application in Parallel-Join Load Balancing" , 22nd Int’l VLDB Conference, Bombay, Ινδία, Σεπτέμβριος 1996.

"Frog and Turtle:  Visual Bridges Between Files and Object-Oriented Data" , 8th Int’l Conference on Scientific and Statistical Database Management, Στοκχόλμη, Σουηδία, Ιούνιος 1996

"Visual User Interfaces for Database Systems" , ACM Workshop on Strategic Directions in Computing Research (HCI Working Group), Cambridge, MA, ΗΠΑ, Ιούνιος 1996

"The FADIVA Benchmark: Version 0" , 3rd FADIVA Workshop, Gubbio, Ιταλία, Μάιος 1996

"User-Oriented Visual Layout at Multiple Granularities" , 3rd Int’l Workshop on Advanced Visual Interfaces, Gubbio, Ιταλία, Μάιος 1996

"Improved Histograms for Query Result Estimation" , Workshop on Performance Enhancement in Object Bases, Dagstuhl, Γερμανία, Απρίλιος 1996