1,134 research outputs found
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
Higher-Order Operator Precedence Languages
Floyd's Operator Precedence (OP) languages are a deterministic context-free
family having many desirable properties. They are locally and parallely
parsable, and languages having a compatible structure are closed under Boolean
operations, concatenation and star; they properly include the family of Visibly
Pushdown (or Input Driven) languages. OP languages are based on three relations
between any two consecutive terminal symbols, which assign syntax structure to
words. We extend such relations to k-tuples of consecutive terminal symbols, by
using the model of strictly locally testable regular languages of order k at
least 3. The new corresponding class of Higher-order Operator Precedence
languages (HOP) properly includes the OP languages, and it is still included in
the deterministic (also in reverse) context free family. We prove Boolean
closure for each subfamily of structurally compatible HOP languages. In each
subfamily, the top language is called max-language. We show that such languages
are defined by a simple cancellation rule and we prove several properties, in
particular that max-languages make an infinite hierarchy ordered by parameter
k. HOP languages are a candidate for replacing OP languages in the various
applications where they have have been successful though sometimes too
restrictive.Comment: In Proceedings AFL 2017, arXiv:1708.0622
Precedence Automata and Languages
Operator precedence grammars define a classical Boolean and deterministic
context-free family (called Floyd languages or FLs). FLs have been shown to
strictly include the well-known visibly pushdown languages, and enjoy the same
nice closure properties. We introduce here Floyd automata, an equivalent
operational formalism for defining FLs. This also permits to extend the class
to deal with infinite strings to perform for instance model checking.Comment: Extended version of the paper which appeared in Proceedings of CSR
2011, Lecture Notes in Computer Science, vol. 6651, pp. 291-304, 2011.
Theorem 1 has been corrected and a complete proof is given in Appendi
Online Recognition of Environment Properties by Using Bilateral Control
The topic of this thesis is identification of the mechanical impedance of an unknown environment. Through the use of bilateral control based on DOB and RFOB structures, position, speed and force information are gathered and analyzed while performing continuous contact with the environment. The nonlinear Hunt-Crossley model is preferred over the classic Kelvin-Voigt model. Particular attention is given to the precise recognition of contact and the detection of an occurring deformation.ope
Integrated Modeling and Verification of Real-Time Systems through Multiple Paradigms
Complex systems typically have many different parts and facets, with
different characteristics. In a multi-paradigm approach to modeling, formalisms
with different natures are used in combination to describe complementary parts
and aspects of the system. This can have a beneficial impact on the modeling
activity, as different paradigms an be better suited to describe different
aspects of the system. While each paradigm provides a different view on the
many facets of the system, it is of paramount importance that a coherent
comprehensive model emerges from the combination of the various partial
descriptions. In this paper we present a technique to model different aspects
of the same system with different formalisms, while keeping the various models
tightly integrated with one another. In addition, our approach leverages the
flexibility provided by a bounded satisfiability checker to encode the
verification problem of the integrated model in the propositional
satisfiability (SAT) problem; this allows users to carry out formal
verification activities both on the whole model and on parts thereof. The
effectiveness of the approach is illustrated through the example of a
monitoring system.Comment: 27 page
Polarising Development – Introducing Alternatives to Neoliberalism and the Crisis
Neoliberal economic policies, with their emphasis on market-led development and individual rationality, have been exposed as bankrupt not only by the global economic crisis but also by increasing social opposition and resistance. Social movements and critical scholars in Latin America, East Asia, Europe and the United States, alongside the Arab uprisings, have triggered renewed debate on possible different futures. While for some years any discussion of substantive alternatives has been marginalised, the global crisis since 2008 has opened up new spaces to debate, and indeed to radically rethink, the meaning of develop- ment. Debates on developmental change are no longer tethered to the pole of ‘reform and reproduce’: a new pole of ‘critique and strategy beyond’ neoliberal capitalism has emerged.
Despite being forcefully challenged, neoliberalism has proven remarkably resilient. In the first years since the crisis erupted, the bulk of the alternative literature pointed to continued growth in the BRICS (Brazil, Russia, India, China and South Africa) and in other big emerging market countries to affirm the necessary role for the state in sustaining capitalist development. New devel- opmental economists have consequently reasserted themselves. Their proposals converged into a broader demand for global Keynesianism (Patomäki, 2012) – a demand that is proving to be less and less realistic in the face of a deepening global economic crisis
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