Section: New Results
Advanced computation models for the Grid
This work is carried out in close co-operation with Pascal Fradet, from Inria Rhône-Alpes (Project-Team POP ART ).
We are considering unconventional approaches for Grid programming and, more generally, for the programming of distributed applications.
It is well known that the task of programming is very difficult in general and even harder when the environment is distributed. As usual, the best way to proceed is by separation of concerns. Programs are first expressed in a model independent of any architecture, and then are refined taking into account the properties of the (distributed) environment. Several properties have to be taken into account, such as correctness, coordination/co-operation, mobility, load balancing, migration, efficiency, security, robustness, time, reliability, availability, computing/communication ratio, etc.
Our present work relies on the chemical reaction paradigm and more precisely on the Gamma model of programming. We believe that this model can be a nice basis for the construction of applications exploiting grid technology.
Our recent contributions include the extension of Gamma to higher-order and the generalization of multiplicity. The extension of the basic Gamma model to a higher-order Gamma makes it possible to consider a Gamma program as a member of a multiset, thus eligible for reactions as any other element of the multiset. We have called this model, the -calculus.
The Grand Challenge in Non-Classical Computation Workshop has been a great opportunity to expose our model, and to have a large overview on non-conventional models of computation. It has also raised some fundamental questions about non-classical programming languages. Revised versions  ,  of the two related articles will be published by the end of this year in the International Journal of Unconventional Computing .
Another generalization of the Gamma language stands in the introduction of multisets with infinite cardinality and multisets with a negative cardinality. These new kind of data structures, combined with the above higher-order properties, provide a very general and powerful tool for expressing very general (and original) coordination schemes. This work has been presented in the International Workshop on Developments in Computational Models which has been published in a volume  of the Electronic Notes in Theoretical Computer Science (ENTCS) series. A complete version of this work has been published in a journal this year  .
We have also published an abstract  in a special issue of Ercim News devoted to ``Emergent Computing''.
Our most recent work concerns task coordination on Grids within the chemical framework. In a first step, applications are programmed in an abstract manner describing essentially the chemical coordination between (not necessarily chemical) software components. In a second step, chemical service programs are specifically provided to the run-time system in order to obtain the expected quality of service from the resources, in terms of efficiency, reliability, security, etc. The implementation of a prototype is being continued.