We add mobility to Place-Transition Petri nets: tokens are names for places, and an input token of a transition can be used in its postset to specify a destination. Mobile Petri nets are then further extended to dynamic nets by adding the possibility of creating new nets during the firing of a transition. In this way, starting from Petri nets, we define a simple hierarchy of nets with increasing degrees of dynamicity. For each class in this hierarchy, we provide its encoding in the former class. Our work was largely inspired by the join-calculus of Fournet and Gonthier, which turns out to be a (well-motivated) particular case of dynamic Petri nets. The main difference is that, in the preset of a transition, we allow both non-linear patterns (name unification) and (locally) free names for input places (that is, we remove the locality constraint, and preserve reflexion).

We consider the structure of the intestinal epithelial tissue and of cell–cell junctions as the biological model inspiring a new class of P systems. First we define the concept of cell polarity, a formal property derived from epithelial cells, which present morphologically and functionally distinct regions of the plasma membrane. Then we show two preliminary results for this new model of computation: on the theoretical side, we show that P systems with cell polarity are computationally (Turing) complete; on the modelling side, we show that the transepithelial movement of glucose from the intestinal lumen into the blood can be described by such a formal system. Finally, we define tissue P systems with cell polarity, where each cell has fixed connections to the neighbouring cells and to the environment, according to both the cell polarity and specific cell–cell junctions.

Several notions of non-interference have been proposed in the literature for studying the problem of confidentiality in concurrent systems. The common feature of these non-interference properties is that they are all defined as extensional properties based on some notion of behavioural equivalence on systems. Here, instead, we address the problem of defining non-interference by looking at the structure of the systems under investigation. We use a simple class of Petri nets, namely, contact-free elementary net systems, as the system model and define structural non-interference properties based on the absence of particular places in the net: such places show that a suitable causality or conflict relation is present between a high-level transition and a low-level one. We characterise one structural property, called PBNI+, which we show to be equivalent to the well-known behavioural property SBNDC. It essentially captures all the positive information flows (that is, a low-level user can deduce that some high-level action has occurred). We start by providing a characterisation of PBNI+ on contact-free elementary net systems, then extend the definition to cope with the richer class of trace nets.

In this paper, we describe a new representation for deterministic rational-valued P systems that allows us to form a bridge between membrane computing and linear algebra. On the one hand, we prove that an efficient computation for these P systems can be described using linear algebra techniques. In particular, we show that the computation for getting a configuration in such P systems can be carried out by multiplying appropriate matrices. On the other hand, we also show that membrane computing techniques can be used to get the nth power of a given matrix.

In this paper we investigate the expressive power of three alternative approaches to the definition of infinite behaviours in process calculi, namely, recursive definitions, replication and iteration. We prove several results discriminating between the calculi obtained from a core CCS by adding the three mechanisms mentioned above. These results are derived by considering the decidability of four basic properties: termination (that is, all computations are finite); convergence (that is, the existence of a finite computation); barb (that is, the ability to perform an action on a given channel) and weak bisimulation. Our results, which are summarised in Table 1, show that the three calculi form a strict expressiveness hierarchy in that: all the properties mentioned are undecidable in CCS with recursion; only termination and barb are decidable in CCS with replication; all the properties are decidable in CCS with iteration. As a corollary, we also obtain a strict expressiveness hierarchy with respect to weak bisimulation, since there exist weak bisimulation preserving encodings of iteration in replication and of replication in recursion, whereas there are no weak bisimulation preserving encodings in the other directions.

The aim of the research domain known as process mining is to use process discovery to construct a process model as an abstract representation of event logs. The goal is to build a model (in terms of a Petri net) that can reproduce the logs under consideration, and does not allow different behaviours compared with those shown in the logs. In particular, process mining aims to verify the accuracy of the model design (represented as a Petri net), basically checking whether the same net can be rediscovered. However, the main mining methods proposed in the literature have some drawbacks: the classical α-algorithm is unable to rediscover various nets, while the region-based approach, which can mine them correctly, is too complex. In this paper, we compare different approaches and propose some ideas to counter the weaknesses of the region-based approach.

The calculus of Mobile Ambients was proposed by Cardelli and Gordon as a foundational calculus for mobile computing. Since its introduction, the computational strength and the decidability of properties have been investigated for several fragments and variants of the standard calculus. We consider the problem of reachability and characterise a public (that is, restriction-free) fragment for which it is decidable. This fragment is obtained by removing the open capability and restricting the application of the replication operator to guarded processes only. This decidability result may appear surprising in combination with the fact that the same fragment was shown to be Turing complete by Maffeis and Phillips. Finally, we extend our decidability result in two ways: we first prove the decidability of a more general property called target reachability (according to which the target of interest for the reachability analysis consists of a possibly infinite set of processes) and then show that our decidability results also hold for a more general calculus, which includes the sophisticated communication mechanisms of Boxed Ambients, which is the most relevant variant of Mobile Ambients without the open capability.

Priority is a frequently used feature of many computational systems. In this paper we study the expressiveness of two process algebras enriched with different priority mechanisms. In particular, we consider a finite (that is, recursion-free) fragment of asynchronous CCS with global priority (FAP, for short) and Phillips' CPG (CCS with local priority), and contrast their expressive power with that of two non-prioritised calculi, namely the π-calculus and its broadcast-based version, called bπ. We prove, by means of leader-election-based separation results, that, under certain conditions, there exists no encoding of FAP in π-Calculus or CPG. Moreover, we single out another problem in distributed computing, which we call thelast man standingproblem (LMS for short), that better reveals the gap between the two prioritised calculi above and the two non-prioritised ones, by proving that there exists no parallel-preserving encoding of the prioritised calculi in the non-prioritised calculi retaining anysincere(complete but partially correct, that is, admitting divergence or premature termination) semantics.

Peer-to-peer (P2P) has recently emerged as a promising model for supporting scalable networks composed of autonomous and spontaneously cooperating entities. The key concept in P2P is decentralization: the resources, the services, as well as the control are not in charge of specialized nodes in the network, but each node (called peer in this context) is directly involved in the management of all these aspects. Besides the advantages of decentralization (autonomy, adaptability, collaboration, and dinamicity just to mention few of them) one of the main drawbacks is the impossibility to predict the topology of the network, thus leaving at run-time any decision about the management of the interaction among the peers. For this reason, we consider useful to provide the developers of P2P applications with a high-level coordination language to be exploited to program the coordination among the peers. In this paper, we present [Formula: see text], a new data-driven coordination model suitable for P2P networks, and we describe [Formula: see text], an implementation of the [Formula: see text] coordination model based on the JXTA peer-to-peer technology.

In this paper we introduce a truly concurrent semantics for P/T nets with inhibitor and read arcs, called henceforth Contextual P/T nets. The semantics is based on a proper extension of the notion of process to cope with read and inhibitor arcs: we s

Extended Markovian Process Algebra (EMPA) is a stochastic process algebra equipped with an interleaving semantics, a Markovian semantics and a net semantics. The main drawback of its net semantics is that is usually associates huge nets with EMPA terms. Here we propose a new net semantics, based on contextual nets, in order to obtain more compact net representations for EMPA terms.