OBSERVING DISTRIBUTION IN PROCESSES: STATIC AND DYNAMIC LOCALITIES

Abstract

The distributed structure of CCS processes can be made explicit by assigning different locations to their parallel components. These locations then become part of what is observed of a process. The assignment of locations may be done statically, or dynamically as the execution proceeds. The dynamic approach was developed first, in Refs. [4,5], as it appeared to be more convenient for defining notions of location equivalence and preorder. Extending previous work by L. Aceto1 we study here the static approach, which is more natural from an intuitive point of view, and more manageable for verification purposes. We define static notions of location equivalence and preorder, and show that they coincide with the dynamic ones. To establish the equivalence of the two location semantics, we introduce an intermediate transition system called occurrence system, which incorporates both notions of locality. This system supports a definition of local history preserving bisimulation for CCS, which is a third formulation of location equivalence.