Nobody would claim that debugging computer software is easy: all too often it proceeds by trial-and-error experiments in which programmers examine the behaviour of the system and form hypotheses that could explain what they see. These problems are exacerbated when developing distributed, peer-to-peer or multi-processor applications, or when unreliable network links form part of the system under test. Environments for pervasive computing take this to an extreme, allowing user-supplied code to run or migrate within and around the network.
Timothy L Harris, University of Cambridge.