Preface Volume 27

AbstractThis volume contains the Proceedings of EXPRESS'99, the sixth International Workshop on Expressiveness in Concurrency. The workshop was held in Eindhoven, The Netherlands, on 23 August 1999, as a satellite event to the CONCUR '99 conference.The EXPRESS workshops aim at bringing together researchers interested in the relations between various formal systems, particularly in the field of Concurrency. More specifically, they focus on the comparison between programming concepts (such as concurrent, functional, imperative, logic and object-oriented programming) and between mathematical models of computation (such as process algebras, Petri nets, event structures, modal logics, rewrite systems etc.) on the basis of their relative expressive power.The EXPRESS workshops were originally held as meetings of the HCM project EXPress which was active with the same focus from January 1994 till December 1997. The first three workshops were held respectively in Amsterdam (1994, chaired by Frits Vaandrager), Tarquinia (1995, chaired by Rocco De Nicola), and Dagstuhl (1996, co-chaired by Ursula Goltz and Rocco De Nicola). The workshop in 1997, which took place in Santa Margherita Ligure and was co-chaired by Catuscia Palamidessi and Joachim Parrow, was organized as a conference with a call for papers and a significant attendance from outside the project. The 1998 workshop, co-chaired by Ilaria Castellani and Catuscia Palamidessi, was held as a satellite workshop of the CONCUR'98 conference in Nice.Like last year, EXPRESS'99 was hosted by the CONCUR conference, this year in Eindhoven. We had 16 submissions, out of which we selected 9 for inclusion in these proceedings. Two of the selected contributions are abstracts. We also had two invited talks, by Prakash Panangaden (McGill University, CA) and Roberto Amadio (Universitacute de Provence, FR).We would like to thank the authors of the submitted papers, the invited speakers, the members of the program committee and their sub-referees for their contribution to both the meeting and this volume. We also would like to thank Eindhoven Technical University for their excellent help with the local organization, and Michael Mislove for his help with the editing of the proceedings.EXPRESS'99 Programme CommitteIlaria Castellani (co-chair, INRIA Sophia-Antipolis, FR)Björn Victor (Uppsala University, SE)Luca Aceto (BRICS, DK)Eric Badouel (INRIA Rennes, FR)Steve Brookes (Carnegie Mellon University, US)Rob van Glabbeek (Stanford University, US)Astrid Kiehn (TU München, DE)Marta Kwiatkowska (University of Birmingham, UK)Ugo Montanari (Università di Pisa, IT)Uwe Nestmann (BRICS, DK)Catuscia Palamidessi (Penn State University, US)Ilaria Castellani and Björn Victor, Guest Editor