Linda[m] and Tiamat: Providing generative communications in a changing world

Abstract

When generative communications, as exemplified by Linda [Gel85], were originally proposed, they were intended as a mechanism for coordination of parallel processes. Since that time, they have been adapted to a variety of distributed environments with great success, as can be seen in commercial systems such as T Spaces [WMLF98]. The time, space and identity decoupling afforded to coordinating entities by generative communications also seems to be ideally suited to mobile environments where devices can come and go frequently and often without warning. Such a rapidly changing environment, however, presents a new set of challenges and attempts to introduce the generative communications paradigm into these environments have, so far, met with limited success. Indeed evaluation of research platforms, such as LIME (Linda In a Mobile Environment) [PMR99.MPR01] and L[2]imbo [DFWB98] have led some to conclude that the generative communication paradigm is not well suited to mobile environments. It is my belief, however, that it is the research platforms in question, rather than the paradigm, which do not fit well with mobile environments. These platforms either attempt to impose tight constraints on an inherently loosely constrained environment, or require significant alterations to the semantics of generative communications. I believe that these systems do not work well as they are not designed around the environment, rather they are forced onto the environment. I will begin by examining why these systems do not suit their environment. This done, I will then show that the conclusions drawn from these systems, namely that generative communications are unsuitable for mobile environments, are incorrect. Further, through construction and examination of a proof of concept system built around an environment-centric design, I will show that generative communications can be provided in a mobile environment with few (minor) semantic alterations. An evaluation of some of the mechanisms used will also be presented along with characterisation of the operation of the system. A comparison with existing mobile solutions will be used to highlight how the environment-driven design results in a system which better suits the nature of the target environment