On the expressiveness of event notification in data-driven coordination languages

Abstract

JavaSpaces and TSpaces are two coordination middlewares for distributed Java programming recently proposed by Sun and IBM, respectively. They are both inspired by the Linda coordination model: processes interact via the emission (out), consumption (in) and the test for absence (inp) of data inside a shared repository. The most interesting improvement introduced by these new products is the event notification mechanism (notify): a process can register interest in the incoming arrivals of a particular kind of data, and then receive communication of the occurrence of these events. We investigate the expressiveness of this new coordination mechanism and we prove that even if event notification strictly increases the expressiveness of a language with only input and output, the obtained language is still strictly less expressive than a language containing also the test for absence.