  Spatial concurrent constraint programming (SCCP) is an algebraic model of
spatial modalities in constrained-based process calculi; it can be used to
reason about spatial information distributed among the agents of a system. This
work presents an executable rewriting logic semantics of SCCP with extrusion
(i.e., process mobility) that uses rewriting modulo SMT, a novel technique that
combines the power of term rewriting, matching algorithms, and SMT-solving. In
this setting, constraints are encoded as formulas in a theory with a
satisfaction relation decided by an SMT solver, while the topology of the
spatial hierarchy is encoded as part of the term structure of symbolic states.
By being executable, the rewriting logic specification offers support for the
inherent symbolic and challenging task of reachability analysis in the
constrained-based model. The approach is illustrated with examples about the
automatic verification of fault-tolerance, consistency, and privacy in
distributed spatial and hierarchical systems.
