Lecture Notes in Computer Science 6075 Commenced Publication in 973 Founding and Former Series Editors: Gerhard Goos. Juris Hartmanis. and Jan van Leeuwen Editorial board David hutchison Lancaster University, UK Takeo kanade Carnegie Mellon University, Pittsburgh, PA, USA Jon M. Kleinberg Cornell University. Ithaca. NY USA Alfred Kobsa University of California, Irvine, CA, USA Friedemann Mattern ETH Zurich. Switzer John C. Mitchell Stanford University, CA, USA Weizmann Institute of Science, Rehovot, Israel University of Bern, Switzerland C. Pandu rangan Indian Institute of Technology, Madras, India TU Dortmund University, Germany Madhu Sudan Microsoft Research, Cambridge, MA, USA Demetri Terzopoulos University of California, Los Angeles, CA, USA Doug t University of California, Berkeley, CA, USA Gerhard Weikum Mar-Planck Institute of Computer Science, Saarbruecken, GermanyLecture Notes in Computer Science 6075 Commenced Publication in 1973 Founding and Former Series Editors: Gerhard Goos, Juris Hartmanis, and Jan van Leeuwen Editorial Board David Hutchison Lancaster University, UK Takeo Kanade Carnegie Mellon University, Pittsburgh, PA, USA Josef Kittler University of Surrey, Guildford, UK Jon M. Kleinberg Cornell University, Ithaca, NY, USA Alfred Kobsa University of California, Irvine, CA, USA Friedemann Mattern ETH Zurich, Switzerland John C. Mitchell Stanford University, CA, USA Moni Naor Weizmann Institute of Science, Rehovot, Israel Oscar Nierstrasz University of Bern, Switzerland C. Pandu Rangan Indian Institute of Technology, Madras, India Bernhard Steffen TU Dortmund University, Germany Madhu Sudan Microsoft Research, Cambridge, MA, USA Demetri Terzopoulos University of California, Los Angeles, CA, USA Doug Tygar University of California, Berkeley, CA, USA Gerhard Weikum Max-Planck Institute of Computer Science, Saarbruecken, Germany