Nomadic Pict: Language and infrastructure design for mobile agents

ii Mobile agents | units of executing computation that can migrate between machines | are likely to become an important enabling technology for fu-ture distributed systems. We study the distributed infrastructures required for location-independent communication between migrating agents. These infrastructures are problematic: the choice or design of an infrastructure must be somewhat application-specic | any given algorithm will only have satisfactory performance for some range of migration and communication behaviour; the algorithms must be matched to the expected properties (and robustness demands) of applications and the failure characteristic of the com-munication medium. To study this problem we introduce an agent program-ming language { Nomadic Pict. It is designed to allow infrastructure al-gorithms to be expressed clearly, as translations from a high-level language to a lower level. The levels are based on rigorously-dened process calculi, which provide sharp levels of abstraction. In this dissertation we describe the language and use it to develop a distributed infrastructure for an ex-ample application. The language and examples have been implemented; we conclude with a description of the compiler and runtime system. iv To Maria and Zdzis law v