253 research outputs found
Multi-weighted Automata Models and Quantitative Logics
Recently, multi-priced timed automata have received much attention for real-time systems. These automata extend priced timed automata by featuring several price parameters. This permits to compute objectives like the optimal ratio between rewards and costs. Arising from the model of timed automata, the multi-weighted setting has also attracted much notice for classical nondeterministic automata.
The present thesis develops multi-weighted MSO-logics on finite, infinite and timed words which are expressively equivalent to multi-weighted automata, and studies decision problems for them. In addition, a Nivat-like theorem for weighted timed automata is proved; this theorem establishes a connection between quantitative and qualitative behaviors of timed automata. Moreover, a logical characterization of timed pushdown automata is given
Timed pushdown automata revisited
This paper contains two results on timed extensions of pushdown automata
(PDA). As our first result we prove that the model of dense-timed PDA of
Abdulla et al. collapses: it is expressively equivalent to dense-timed PDA with
timeless stack. Motivated by this result, we advocate the framework of
first-order definable PDA, a specialization of PDA in sets with atoms, as the
right setting to define and investigate timed extensions of PDA. The general
model obtained in this way is Turing complete. As our second result we prove
NEXPTIME upper complexity bound for the non-emptiness problem for an expressive
subclass. As a byproduct, we obtain a tight EXPTIME complexity bound for a more
restrictive subclass of PDA with timeless stack, thus subsuming the complexity
bound known for dense-timed PDA.Comment: full technical report of LICS'15 pape
Timed Context-Free Temporal Logics
The paper is focused on temporal logics for the description of the behaviour
of real-time pushdown reactive systems. The paper is motivated to bridge
tractable logics specialized for expressing separately dense-time real-time
properties and context-free properties by ensuring decidability and
tractability in the combined setting. To this end we introduce two real-time
linear temporal logics for specifying quantitative timing context-free
requirements in a pointwise semantics setting: Event-Clock Nested Temporal
Logic (EC_NTL) and Nested Metric Temporal Logic (NMTL). The logic EC_NTL is an
extension of both the logic CaRet (a context-free extension of standard LTL)
and Event-Clock Temporal Logic (a tractable real-time logical framework related
to the class of Event-Clock automata). We prove that satisfiability of EC_NTL
and visibly model-checking of Visibly Pushdown Timed Automata (VPTA) against
EC_NTL are decidable and EXPTIME-complete. The other proposed logic NMTL is a
context-free extension of standard Metric Temporal Logic (MTL). It is well
known that satisfiability of future MTL is undecidable when interpreted over
infinite timed words but decidable over finite timed words. On the other hand,
we show that by augmenting future MTL with future context-free temporal
operators, the satisfiability problem turns out to be undecidable also for
finite timed words. On the positive side, we devise a meaningful and decidable
fragment of the logic NMTL which is expressively equivalent to EC_NTL and for
which satisfiability and visibly model-checking of VPTA are EXPTIME-complete.Comment: In Proceedings GandALF 2018, arXiv:1809.02416. arXiv admin note: A
technical report with full details is available at arXiv:1808.0427
Verification for Timed Automata extended with Unbounded Discrete Data Structures
We study decidability of verification problems for timed automata extended
with unbounded discrete data structures. More detailed, we extend timed
automata with a pushdown stack. In this way, we obtain a strong model that may
for instance be used to model real-time programs with procedure calls. It is
long known that the reachability problem for this model is decidable. The goal
of this paper is to identify subclasses of timed pushdown automata for which
the language inclusion problem and related problems are decidable
Zenoness for Timed Pushdown Automata
Timed pushdown automata are pushdown automata extended with a finite set of
real-valued clocks. Additionaly, each symbol in the stack is equipped with a
value representing its age. The enabledness of a transition may depend on the
values of the clocks and the age of the topmost symbol. Therefore, dense-timed
pushdown automata subsume both pushdown automata and timed automata. We have
previously shown that the reachability problem for this model is decidable. In
this paper, we study the zenoness problem and show that it is EXPTIME-complete.Comment: In Proceedings INFINITY 2013, arXiv:1402.661
Generalizing input-driven languages: theoretical and practical benefits
Regular languages (RL) are the simplest family in Chomsky's hierarchy. Thanks
to their simplicity they enjoy various nice algebraic and logic properties that
have been successfully exploited in many application fields. Practically all of
their related problems are decidable, so that they support automatic
verification algorithms. Also, they can be recognized in real-time.
Context-free languages (CFL) are another major family well-suited to
formalize programming, natural, and many other classes of languages; their
increased generative power w.r.t. RL, however, causes the loss of several
closure properties and of the decidability of important problems; furthermore
they need complex parsing algorithms. Thus, various subclasses thereof have
been defined with different goals, spanning from efficient, deterministic
parsing to closure properties, logic characterization and automatic
verification techniques.
Among CFL subclasses, so-called structured ones, i.e., those where the
typical tree-structure is visible in the sentences, exhibit many of the
algebraic and logic properties of RL, whereas deterministic CFL have been
thoroughly exploited in compiler construction and other application fields.
After surveying and comparing the main properties of those various language
families, we go back to operator precedence languages (OPL), an old family
through which R. Floyd pioneered deterministic parsing, and we show that they
offer unexpected properties in two fields so far investigated in totally
independent ways: they enable parsing parallelization in a more effective way
than traditional sequential parsers, and exhibit the same algebraic and logic
properties so far obtained only for less expressive language families
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