arXiv subjects

Marco Peressotti

Publications and source records attributed to Marco Peressotti.

46 records · Page 3Linked to original sources

arXiv2017

On the trade-off between labels and weights in quantitative bisimulation

Reductions for transition systems have been recently introduced as a uniform and principled method for comparing the expressiveness of system models with respect to a range of properties, especially bisimulations. In this paper we study the expressiveness (w.r.t. bisimulations) of models for quantitative computations such as weighted labelled transition systems (WLTSs), uniform labelled transition systems (ULTraSs), and state-to-function transition systems (FuTSs). We prove that there is a trade-off between labels and weights: at one extreme lays the class of (unlabelled) weighted transition systems where information is presented using weights only; at the other lays the class of labelled transition systems (LTSs) where information is shifted on labels. These categories of systems cannot be further reduced in any significant way and subsume all the aforementioned models.

cs.LO↗

arXiv2017

Reductions for Transition Systems at Work: Deriving a Logical Characterization of Quantitative Bisimulation

Weighted labelled transition systems (WLTSs) are an established meta-model aiming to provide general results and tools for a wide range of systems such as non-deterministic, stochastic, and probabilistic systems. In order to encompass processes combining several quantitative aspects, extensions of the WLTS framework have been further proposed, state-to-function transition systems (FuTSs) and uniform labelled transition systems (ULTraSs) being two prominent examples. In this paper we show that this hierarchy of meta-models collapses when studied under the lens of bisimulation-coherent encodings. Taking advantage of these reductions, we derive a fully abstract Hennessy-Milner-style logic for FuTSs, i.e., which characterizes quantitative bisimilarity, from a fully-abstract logic for WLTSs.

cs.LO↗

arXiv2016

Endofunctors modelling higher-order behaviours

In this paper we show how the abstract behaviours of higher-order systems can be modelled as final coalgebras of suitable behavioural functors. These functors have the challenging peculiarity to be circularly defined with their own final coalgebra. Our main contribution is a general construction for defining these functors, solving this circularity which is the essence of higher-order behaviours. This characterisation is syntax agnostic. To achieve this property, we shift from term passing to behaviour passing: in the former higher-order is expressed by passing around syntactic objects (such as terms or processes) as representations of behaviours whereas the former ditches the syntactic encoding altogether and works directly with behaviours i.e. semantic objects. From this perspective, the former can be seen as syntactic higher-order whereas the later as semantic higher-order.

cs.LO↗

arXiv2016

A Specification of Open Transactional Memory for Haskell

Transactional memory (TM) has emerged as a promising abstraction for concurrent programming alternative to lock-based synchronizations. However, most TM models admit only isolated transactions, which are not adequate in multi-threaded programming where transactions have to interact via shared data before committing. In this paper, we present Open Transactional Memory (OTM), a programming abstraction supporting safe, data-driven interactions between composable memory transactions. This is achieved by relaxing isolation between transactions, still ensuring atomicity: threads of different transactions can interact by accessing shared variables, but then their transactions have to commit together-actually, these transactions are transparently merged. This model allows for loosely-coupled interactions since transaction merging is driven only by accesses to shared data, with no need to specify participants beforehand. In this paper we provide a specification of the OTM in the setting of Concurrent Haskell, showing that it is a conservative extension of current STM abstraction. In particular, we provide a formal semantics, which allows us to prove that OTM satisfies the \emph{opacity} criterion.

cs.PL↗

arXiv2015

Behavioural equivalences for coalgebras with unobservable moves

We introduce a general categorical framework for the definition of weak behavioural equivalences, building on and extending recent results in the field. This framework is based on parametrized saturation categories, i.e. categories whose hom-sets are endowed with complete orders and a suitable iteration operators; this structure allows us to provide the abstract definitions of various (weak) behavioural equivalence. We show that the Kleisli categories of many common monads are categories of this kind. This allows us to readily instantiate the abstract definitions to a wide range of existing systems (weighted LTS, Segala systems, calculi with names, etc.), recovering the corresponding notions of weak behavioural equivalences. Moreover, we can provide neatly new weak behavioural equivalences for more complex behaviours, like those definable on topological spaces, measurable spaces, etc.

cs.LO↗

arXiv2015

Structural operational semantics for non-deterministic processes with quantitative aspects

General frameworks have been recently proposed as unifying theories for processes combining non-determinism with quantitative aspects (such as probabilistic or stochastically timed executions), aiming to provide general results and tools. This paper provides two contributions in this respect. First, we present a general GSOS specification format and a corresponding notion of bisimulation for non-deterministic processes with quantitative aspects. These specifications define labelled transition systems according to the ULTraS model, an extension of the usual LTSs where the transition relation associates any source state and transition label with state reachability weight functions (like, e.g., probability distributions). This format, hence called Weight Function GSOS (WF-GSOS), covers many known systems and their bisimulations (e.g. PEPA, TIPP, PCSP) and GSOS formats (e.g. GSOS, Weighted GSOS, Segala-GSOS, among others). The second contribution is a characterization of these systems as coalgebras of a class of functors, parametric on the weight structure. This result allows us to prove soundness and completeness of the WF-GSOS specification format, and that bisimilarities induced by these specifications are always congruences.

cs.LO↗

arXiv2015

Open Transactions on Shared Memory

Transactional memory has arisen as a good way for solving many of the issues of lock-based programming. However, most implementations admit isolated transactions only, which are not adequate when we have to coordinate communicating processes. To this end, in this paper we present OCTM, an Haskell-like language with open transactions over shared transactional memory: processes can join transactions at runtime just by accessing to shared variables. Thus a transaction can co-operate with the environment through shared variables, but if it is rolled-back, also all its effects on the environment are retracted. For proving the expressive power of TCCS we give an implementation of TCCS, a CCS-like calculus with open transactions.

cs.PL↗

arXiv2015

Distributed execution of bigraphical reactive systems

The bigraph embedding problem is crucial for many results and tools about bigraphs and bigraphical reactive systems (BRS). Current algorithms for computing bigraphical embeddings are centralized, i.e. designed to run locally with a complete view of the guest and host bigraphs. In order to deal with large bigraphs, and to parallelize reactions, we present a decentralized algorithm, which distributes both state and computation over several concurrent processes. This allows for distributed, parallel simulations where non-interfering reactions can be carried out concurrently; nevertheless, even in the worst case the complexity of this distributed algorithm is no worse than that of a centralized algorithm.

cs.DC↗

arXiv2014

GSOS for non-deterministic processes with quantitative aspects

Recently, some general frameworks have been proposed as unifying theories for processes combining non-determinism with quantitative aspects (such as probabilistic or stochastically timed executions), aiming to provide general results and tools. This paper provides two contributions in this respect. First, we present a general GSOS specification format (and a corresponding notion of bisimulation) for non-deterministic processes with quantitative aspects. These specifications define labelled transition systems according to the ULTraS model, an extension of the usual LTSs where the transition relation associates any source state and transition label with state reachability weight functions (like, e.g., probability distributions). This format, hence called Weight Function SOS (WFSOS), covers many known systems and their bisimulations (e.g. PEPA, TIPP, PCSP) and GSOS formats (e.g. GSOS, Weighted GSOS, Segala-GSOS, among others). The second contribution is a characterization of these systems as coalgebras of a class of functors, parametric on the weight structure. This result allows us to prove soundness of the WFSOS specification format, and that bisimilarities induced by these specifications are always congruences.

cs.LO↗

arXiv2013

Weak bisimulations for labelled transition systems weighted over semirings

Weighted labelled transition systems are LTSs whose transitions are given weights drawn from a commutative monoid. WLTSs subsume a wide range of LTSs, providing a general notion of strong (weighted) bisimulation. In this paper we extend this framework towards other behavioural equivalences, by considering semirings of weights. Taking advantage of this extra structure, we introduce a general notion of weak weighted bisimulation. We show that weak weighted bisimulation coincides with the usual weak bisimulations in the cases of non-deterministic and fully-probabilistic systems; moreover, it naturally provides a definition of weak bisimulation also for kinds of LTSs where this notion is currently missing (such as, stochastic systems). Finally, we provide a categorical account of the coalgebraic construction of weak weighted bisimulation; this construction points out how to port our approach to other equivalences based on different notion of observability.

cs.LO↗