61 research outputs found
P and dP Automata: A Survey
This is a quick survey of basic notions and results related to P automata (P systems with symport/antiport rules working in the accepting mode), with some emphasis on the recently introduced dP automata (a distributed version of the standard P automata), ending with some open problems and research topics which we find of interest in this area.Junta de AndalucĂa P08 – TIC 0420
Session Coalgebras: A Coalgebraic View on Regular and Context-Free Session Types
Compositional methods are central to the verification of software systems. For concurrent and communicating systems, compositional techniques based on behavioural type systems have received much attention. By abstracting communication protocols as types, these type systems can statically check that channels in a program interact following a certain protocol—whether messages are exchanged in the intended order. In this article, we put on our coalgebraic spectacles to investigate session types, a widely studied class of behavioural type systems. We provide a syntax-free description of session-based concurrency as states of coalgebras. As a result, we rediscover type equivalence, duality, and subtyping relations in terms of canonical coinductive presentations. In turn, this coinductive presentation enables us to derive a decidable type system with subtyping for the π-calculus, in which the states of a coalgebra will serve as channel protocols. Going full circle, we exhibit a coalgebra structure on an existing session type system, and show that the relations and type system resulting from our coalgebraic perspective coincide with existing ones. We further apply to session coalgebras the coalgebraic approach to regular languages via the so-called rational fixed point, inspired by the trinity of automata, regular languages, and regular expressions with session coalgebras, rational fixed point, and session types, respectively. We establish a suitable restriction on session coalgebras that determines a similar trinity, and reveals the mismatch between usual session types and our syntax-free coalgebraic approach. Furthermore, we extend our coalgebraic approach to account for context-free session types, by equipping session coalgebras with a stack
Session Coalgebras: A Coalgebraic View on Session Types and Communication Protocols
Compositional methods are central to the development and verification of
software systems. They allow to break down large systems into smaller
components, while enabling reasoning about the behaviour of the composed
system. For concurrent and communicating systems, compositional techniques
based on behavioural type systems have received much attention. By abstracting
communication protocols as types, these type systems can statically check that
programs interact with channels according to a certain protocol, whether the
intended messages are exchanged in a certain order. In this paper, we put on
our coalgebraic spectacles to investigate session types, a widely studied class
of behavioural type systems. We provide a syntax-free description of
session-based concurrency as states of coalgebras. As a result, we rediscover
type equivalence, duality, and subtyping relations in terms of canonical
coinductive presentations. In turn, this coinductive presentation makes it
possible to elegantly derive a decidable type system with subtyping for
-calculus processes, in which the states of a coalgebra will serve as
channel protocols. Going full circle, we exhibit a coalgebra structure on an
existing session type system, and show that the relations and type system
resulting from our coalgebraic perspective agree with the existing ones.Comment: 36 pages, submitte
Languages and P Systems: Recent Developments
Languages appeared from the very beginning in membrane computing, by
their length sets or directly as sets of strings. We briefly recall here this relationship, with
some details about certain recent developments. In particular, we discuss the possibility
to associate a control word with a computation in a P system. An improvement of a result
concerning the control words of spiking neural P systems is given: regular languages can
be obtained as control words of such systems with only four neurons (and with usual
extended rules: no more spikes are produces than consumed). Several research topics are
pointed out.Junta de AndalucĂa P08 – TIC 0420
Frontiers of Membrane Computing: Open Problems and Research Topics
This is a list of open problems and research topics collected after the Twelfth
Conference on Membrane Computing, CMC 2012 (Fontainebleau, France (23 - 26 August
2011), meant initially to be a working material for Tenth Brainstorming Week on
Membrane Computing, Sevilla, Spain (January 30 - February 3, 2012). The result was
circulated in several versions before the brainstorming and then modified according to
the discussions held in Sevilla and according to the progresses made during the meeting.
In the present form, the list gives an image about key research directions currently active
in membrane computing
Session coalgebras: A coalgebraic view on session types and communication protocols
Compositional methods are central to the development and verification of software systems. They allow breaking down large systems into smaller components, while enabling reasoning about the behaviour of the composed system. For concurrent and communicating systems, compositional techniques based on behavioural type systems have received much attention. By abstracting communication protocols as types, these type systems can statically check that programs interact with channels according to a certain protocol, whether the intended messages are exchanged in a certain order. In this paper, we put on our coalgebraic spectacles to investigate session types, a widely studied class of behavioural type systems. We provide a syntax-free description of session-based concurrency as states of coalgebras. As a result, we rediscover type equivalence, duality, and subtyping rela
Provable randomized rounding for minimum-similarity diversification
When searching for information in a data collection, we are often interested not only in finding relevant items, but also in assembling a diverse set, so as to explore different concepts that are present in the data. This problem has been researched extensively. However, finding a set of items with minimal pairwise similarities can be computationally challenging, and most existing works striving for quality guarantees assume that item relatedness is measured by a distance function. Given the widespread use of similarity functions in many domains, we believe this to be an important gap in the literature. In this paper we study the problem of finding a diverse set of items, when item relatedness is measured by a similarity function. We formulate the diversification task using a flexible, broadly applicable minimization objective, consisting of the sum of pairwise similarities of the selected items and a relevance penalty term. To find good solutions we adopt a randomized rounding strategy, which is challenging to analyze because of the cardinality constraint present in our formulation. Even though this obstacle can be overcome using dependent rounding, we show that it is possible to obtain provably good solutions using an independent approach, which is faster, simpler to implement and completely parallelizable. Our analysis relies on a novel bound for the ratio of Poisson-Binomial densities, which is of independent interest and has potential implications for other combinatorial-optimization problems. We leverage this result to design an efficient randomized algorithm that provides a lower-order additive approximation guarantee. We validate our method using several benchmark datasets, and show that it consistently outperforms the greedy approaches that are commonly used in the literature.Peer reviewe
An Improvement of the Piggyback Algorithm for Parallel Model Checking
This paper extends the piggyback algorithm to enlarge the set of liveness properties it can verify. Its extension is motivated by an attempt to express in logic the counterexamples it can detect and relate them to bounded liveness. The original algorithm is based on parallel breadth-first search and piggybacking of accepting states that are deleted after counting a fixed number of transitions. The main improvement is obtained by renewing the counter of transitions when the same accepting states are visited in the negated property automaton. In addition, we describe piggybacking of multiple states in either sets (exact) or Bloom filters (lossy but conservative), and use of local searches that attempt to connect cycles fragmented among processing cores. Finally it is proved that accepting cycle detection is in NC in the size of the product automaton's entire state space, including unreachable states
Data parallel string manipulating programs
String-manipulating programs are an important class of programs with applications in malware detection, graphics, input sanitization for Web security, and large-scale HTML processing. This paper extends prior work on BEK, an expressive domain-specific language for writing string-manipulating programs, with algorithmic insights that make BEK both analyzable and data-parallel. By analyzable we mean that unlike most general purpose programming languages, many algebraic properties of a BEK program are decidable (i.e., one can check whether two programs commute or compute the inverse of a program). By data-parallel we mean that a BEK program can compute on arbitrary subsections of its input in parallel, thus exploiting parallel hardware. This latter requirement is particularly important for programs which operate on large data: without data parallelism, a programmer cannot hide the latency of reading data from various storage media (i.e., reading a terabyte of data from a modern hard drive takes about 3 hours). With a data-parallel approach, the system can split data across multiple disks and thus hide the latency of reading the data. A BEK program is expressive: a programmer can use conditionals, switch statements, and registers--or local variables--in order to implement common string-manipulating programs. Unfortunately, this expressivity induces data dependencies, which are an obstacle to parallelism. The key contribution of this paper is an algorithm which automatically removes these data dependencies by mapping a B EK program into a intermediate format consisting of symbolic transducers, which extend classical transducers with symbolic predicates and symbolic assignments. We present a novel algorithm that we call exploration which performs symbolic loop unrolling of these transducers to obtain simplified versions of the original program. We show how these simplified versions can then be lifted to a stateless form, and from there compiled to data-parallel hardware. To evaluate the efficacy of our approach, we demonstrate up to 8x speedups for a number of real-world, BEK programs, (e.g., HTML encoder and decoder) on data-parallel hardware. To the best of our knowledge, these are the first data parallel implementation of these programs. To validate that our approach is correct, we use an automatic testing technique to compare our generated code to the original implementations and find no semantic deviations
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