Lime: Linda in a Mobile Environment

Lime is a Java-based middleware that provides a coordination layer that can be exploited for designing applications which exhibit either logical or physical mobility---or both. Lime is specifically targeted toward the complexities of the ad hoc mobile environment, however it is applicable beyond this scope. The driving force in the development of Lime has been the observation that application design in the physical and logical mobile environments is complicated due to the constant changes in the availability of resources (both data and computational elements) as hosts move through space and mobile agents move among hosts. Our goal was to simplify programming in this constantly changing environment by providing a middleware to handle on behalf of the programmer many of the complexities, while still revealing enough of the interesting aspects of the mobile environment to remain flexible and applicable to a wide variety of development projects.

With this goal, we turned toward Linda, a shared memory computing model developed in the mid 1980's at Yale University, which simplifies distributed computing. Our idea is to provide the simple Linda model of coordination in the mobile environment. The result of our investigation is Lime: Linda in a Mobile environment.

In Linda, processes communicate by writing, reading, and removing data from a tuple space that is assumed to be persistent and globally shared among all processes. Lime adapts this notion to a mobile environment by breaking up the notion of a global tuple space, and distributing its contents across multiple mobile components. When components are within range (i.e., mobile agents are on the same host or communication is available between mobile hosts that contain agents), the contents of the tuple spaces held by the individual mobile components are transiently and transparently shared, forming a federated tuple space. The content accessible through such virtual tuple space, made up of the concrete tuple spaces contributed by each component, changes from time to time according to the current connectivity pattern. Lime also introduces the notions of tuple location, for querying a partition of the federated tuple space, and of reactive programming, for allowing actions to be performed with varying degrees of atomicity upon insertion of a tuple.

The current implementation is kept independent from both the underlying support for mobile agents and the underlying tuple space implementation. In the first case, an adaptation layer is directly provided in Lime that allows integration of virtually any mobile agent system. The current release provides an adapter for the µCode mobile code system. As for tuple spaces, Lime leverages off of the LighTS package, a tuple space implementation that offers also an adaptation layer allowing one to use a different tuple space implementation without changing the interface. Both µCode and LighTS have been designed and implemented by one of the Lime authors as separate projects independent from Lime, and are available as open source on SourceForge.

We hope that you will find the Lime model amenable to the styles of mobile programs that you want to write. To learn more, see how it works, or jump into the API documentation to figure it out. You can also download it and run the examples. Lime is open source, with the use of the binaries and source code regulated by the GNU Lesser Public License.

LIME: Linda in a Mobile Environment