Toward a Formal Semantics for Grid Computing Marco Aldinucci Institute of Information Science and Technologies National Research Council, Via Moruzzi 1, I-56124 Pisa, Italy Emilio Tuosto Dipartimento di Informatica, Universit` a di Pisa, Via Buonarroti 2, I-56127 Pisa, Italy {aldinuc,etuosto}@di.unipi.it Abstract Current Grid-aware applications are developed on existing soft- ware infrastructures, such as Globus, by developers who are experts on Grid software implementation. Although many useful applications have been produced this way, this approach requires a level of expertise that will make it difficult for Grid computing to achieve widespread acceptance. The problem is faced in a number of current research projects that are targeted to raise the abstraction level in Grid pro- gramming. A major weakness of the current high-level parallel pro- gramming and Grid targeted systems is that semantics is usually pro- vided in an informal way, thus preventing any formal reasoning about program behavior. We describe a semantical model based on (hy- per)graph rewriting suitable for the description of both functional and parallel semantics of that is aimed at filling this gap. 1 Introduction Grid computing is supposed to enable the development of large scientific ap- plications on an unprecedent scale. The key idea behind Grid-aware applica- tions consists in making use of the aggregate power of distributed resources, thus benefiting from a computing power that falls far beyond the current availability threshold in a single site. Despite the huge computing power potentially available on the Grid, developing algorithms able to exploit it is currently likely to be a hard task. To realize the potential, programmers must design highly concurrent algorithms that can execute on large-scale 1