7 research outputs found
Bisimilarity in Fresh-Register Automata
Research supported by the Engineering and Physical Sciences Research Council (EP/J019577/1) and the Royal Academy of Engineering (RF: Tzevelekos)
Synthesis of Data Word Transducers
In reactive synthesis, the goal is to automatically generate an
implementation from a specification of the reactive and non-terminating
input/output behaviours of a system. Specifications are usually modelled as
logical formulae or automata over infinite sequences of signals
(-words), while implementations are represented as transducers. In the
classical setting, the set of signals is assumed to be finite. In this paper,
we consider data -words instead, i.e., words over an infinite alphabet.
In this context, we study specifications and implementations respectively given
as automata and transducers extended with a finite set of registers. We
consider different instances, depending on whether the specification is
nondeterministic, universal or deterministic, and depending on whether the
number of registers of the implementation is given or not.
In the unbounded setting, we show undecidability for both universal and
nondeterministic specifications, while decidability is recovered in the
deterministic case. In the bounded setting, undecidability still holds for
nondeterministic specifications, but can be recovered by disallowing tests over
input data. The generic technique we use to show the latter result allows us to
reprove some known result, namely decidability of bounded synthesis for
universal specifications
Symbolic Register Automata
Symbolic Finite Automata and Register Automata are two orthogonal extensions
of finite automata motivated by real-world problems where data may have
unbounded domains. These automata address a demand for a model over large or
infinite alphabets, respectively. Both automata models have interesting
applications and have been successful in their own right. In this paper, we
introduce Symbolic Register Automata, a new model that combines features from
both symbolic and register automata, with a view on applications that were
previously out of reach. We study their properties and provide algorithms for
emptiness, inclusion and equivalence checking, together with experimental
results
Computer Aided Verification
This open access two-volume set LNCS 11561 and 11562 constitutes the refereed proceedings of the 31st International Conference on Computer Aided Verification, CAV 2019, held in New York City, USA, in July 2019. The 52 full papers presented together with 13 tool papers and 2 case studies, were carefully reviewed and selected from 258 submissions. The papers were organized in the following topical sections: Part I: automata and timed systems; security and hyperproperties; synthesis; model checking; cyber-physical systems and machine learning; probabilistic systems, runtime techniques; dynamical, hybrid, and reactive systems; Part II: logics, decision procedures; and solvers; numerical programs; verification; distributed systems and networks; verification and invariants; and concurrency
Bisimilarity in fresh-register automata.
Register automata are a basic model of computation over infinite alphabets.
Fresh-register automata extend register automata with the capability to
generate fresh symbols in order to model computational scenarios involving name
creation. This paper investigates the complexity of the bisimilarity problem
for classes of register and fresh-register automata. We examine all main
disciplines that have appeared in the literature: general register assignments;
assignments where duplicate register values are disallowed; and assignments
without duplicates in which registers cannot be empty. In the general case, we
show that the problem is EXPTIME-complete.
However, the absence of duplicate values in registers enables us to identify
inherent symmetries inside the associated bisimulation relations, which can be
used to establish a polynomial bound on the depth of Attacker-winning
strategies. Furthermore, they enable a highly succinct representation of the
corresponding bisimulations. By exploiting results from group theory and
computational group theory, we can then show solvability in PSPACE and NP
respectively for the latter two register disciplines. In each case, we find
that freshness does not affect the complexity class of the problem.
The results allow us to close a complexity gap for language equivalence of
deterministic register automata. We show that deterministic language
inequivalence for the no-duplicates fragment is NP-complete, which disproves an
old conjecture of Sakamoto.
Finally, we discover that, unlike in the finite-alphabet case, the addition
of pushdown store makes bisimilarity undecidable, even in the case of visibly
pushdown storage