Specification and execution of declarative policies for grid service selection

We describe a modified Grid architecture that allows to specify and enforce connection policies with preferences and integrity constraints. This is done by interposing a policy enforcement engine between a calling application and the relative client stubs. Such policies are conveniently expressed in the declarative policy specification language PPDL. In particular, PPDL allows expressing preferences on how to enforce constraints on action execution. PPDL policies are evaluated by translating them into a Logic Program with Ordered Disjunctions and calling the psmodels interpreter. We describe an experimental architecture that enforces connection policies by catching and filtering only service requests. The process is completely transparent to both client applications and Grid services. There are clear advantages in having the connection logic expressed declaratively and externally to applications.