Separability, expressiveness, and decidability in the ambient logic

The Ambient Logic (AL) has been proposed for expressing properties of process mobility in the calculus of Mobile Ambients (MA), and as a basis for query languages on semistructured data. We study some basic questions concerning the descriptive and discriminating power of AL, focusing on the equivalence on processes induced by the logic (=/sub L/). We consider MA, and two Turing complete subsets of it, MA/sub IF/ and MA/sub IF//sup syn/, respectively defined by imposing a semantic and a syntactic constraint on process prefixes. The main contributions include: coinductive and inductive operational characterisations of =/sub L/; an axiomatisation of =/sub L/ on MA/sub IF//sup syn/; the construction of characteristic formulas for the processes in MA/sub IF/ with respect to =/sub L/; the decidability of =/sub L/ on MA/sub IF/ and on MA/sub IF//sup syn/, and its undecidability on MA.