Maria Grazia Vigliotti

On Reduction Semantics for the Push and Pull Ambitent Calculus

Honda and Yoshida showed how to obtain a meaningful equivalence on processes in the asynchronous π-calculus using equational theories identifying insensitive processes. We apply their approach to a dialect of Cardelli and Gordon’s Mobile Ambients. The version we propose here is the Push and Pull Ambient Calculus, where the operational semantics is no longer defined in terms of ambients entering and exiting other ambients, but in terms of being pulled and being pushed away by another ambient. Like the standard ambient calculus, this dialect has the computational power of the asynchronous π-calculus. We contend that the new calculus allows a better modelling of certain security issues.

Electoral Systems in Ambient Calculi

This paper compares the expressiveness of ambient calculi against different dialects of the pi-calculus. Cardelli and Gordon encoded the asynchronous pi-calculus into their calculus of Mobile Ambients (MA). Zimmer has shown that the synchronous pi-calculus without choice can be encoded in pure (no communication) Safe Ambients. We show that pure MA without restriction has symmetric electoral systems, that is, it is possible to solve the problem of electing a leader in a symmetric network. By the work of Palamidessi, this implies that pure MA without restriction is not encodable (under certain conditions) in the pi-calculus with separate choice. We adapt the work of Carbone and Maffeis to show that pure MA cannot be encoded (under certain other conditions) into the pi-calculus with mixed choice (but without matching).

Tutorial on separation results in process calculi via leader election problems

We compare the expressive power of process calculi by studying the problem of electing a leader in a symmetric network of processes. We consider the @p-calculus with mixed choice, separate choice and internal mobility, value-passing CCS and Mobile Ambients, together with other ambient calculi (Safe Ambients, the Push and Pull Ambient Calculus and Boxed Ambients). We provide a unified approach for all these calculi using reduction semantics.

Leader election in rings of ambient processes

Palamidessi has shown that the π-calculus with mixed choice is powerful enough to solve the leader election problem on a symmetric ring of processes. We show that this is also possible in the calculus of Mobile Ambients (MA), without using communication or restriction. Following Palamidessis methods, we deduce that there is no encoding satisfying certain conditions from MA into CCS. We also show that the calculus of Boxed Ambients is more expressive than its communication-free fragment.

A general result for deriving product-form solutions in markovian models

In this paper we provide a general method to derive product-form solutions for stochastic models. We take inspiration from the Reversed Compound Agent Theorem and we provide a different formulation using labeled automata, a generalization which encompasses a bigger class of product-form solutions, and a new proof based on the solution of the system of global balance equations. We show that our result may have practical applications in the performance evaluation of complex software and hardware architectures and can be the base for the development of new analysis tools or the extension of existing ones.

Probabilistic Mobile Ambients

The calculus of Mobile Ambients has been introduced for expressing mobility and mobile computation. In this paper we present a probabilistic version of Mobile Ambients by augmenting the syntax of the original Ambient Calculus with a (guarded) probabilistic choice operator. To allow for the representation of both the probabilistic behaviour introduced through the new probabilistic choice operator and the nondeterminism present in the original Ambient Calculus we use probabilistic automata as the underpinning semantic model. The Ambient logic is a logic for Mobile Ambients that contains a novel treatment of both locations and hidden names. For specifying properties of Probabilistic Mobile Ambients, we extend this logic to specify probabilistic behaviour. In addition, to show the utility of our approach we present an example of a virus infecting a network.

Symmetric electoral systems for ambient calculi

This paper compares the expressiveness of different fragments of ambient calculi via leader election problems. We consider Mobile Ambients (MA), Safe Ambients (SA) and the Push and Pull Ambient Calculus (PAC). Cardelli and Gordon encoded the asynchronous @p-calculus into MA. Zimmer has shown that the synchronous @p-calculus without choice can be encoded in pure (no communication) SA. We show that pure MA without restriction has symmetric electoral systems, that is, it is possible to solve the problem of electing a leader in a symmetric network. By the work of Palamidessi, this implies that this fragment of MA is not encodable (under certain conditions) in the @p-calculus with separate choice. Moreover, we use the same technique to show that fragments of SA and PAC are not encodable (under certain conditions) in the @p-calculus with separate choice. We also show that particular fragments of ambient calculi do not admit a solution to leader election problems, in the same way as the @p-calculus with separate choice. This yields a fine-grained hierarchy within ambient calculi.

Barbs and Congruences for Safe Mobile Ambients

Abstract The Ambient Calculus offers many ways in which processes can interact and be observed. In the context of Levi and Sangiorgis Safe Mobile Ambients (SA), the extra co-capabilities required for interaction complicate the fundamental observations. We show that different formulations of barbs lead to the same barbed congruence. We prove this by following Honda and Yoshidas approach for the π-calculus by defining the insensitive terms of SA.

Discovery of anomalous behaviour in temporal networks

Abstract In this work we consider the problem of detecting anomalous behaviour and present a novel approach that allows ‘behaviour’ to be classified as either to be normal or abnormal by checking the p -value associated with the occurrence of the behaviour which is modelled following a binomial distribution within a discrete time model. We investigate the problem of detecting anomalous behaviour by looking at how communication evolves over time in a social network graph. Under the assumption that some nodes of the network could be labelled qualitatively, we present a novel approach that allows us to infer a subset of nodes of the social network which might share the same qualitative connotation. In other words, assuming one or more members belong to some criminal organisation, we wish to investigate how many other persons belong to the same organisation. We have tested our method in two datasets, VAST2008 and a Twitter Dataset (data collected in 2012), with encouraging results.

A Logical Interpretation of the λ-Calculus into the η-Calculus, Preserving Spine Reduction and Types

We define a new, output-based encoding of the λ -calculus into the asynchronous η -calculus --- enriched with pairing --- that has its origin in mathematical logic, and show that this encoding respects one-step spine-reduction up to substitution, and that normal substitution is respected up to similarity. We will also show that it fully encodes lazy reduction of closed terms, in that term-substitution as well as each reduction step are modelled up to similarity. We then define a notion of type assignment for the η -calculus that uses the type constructor →, and show that all Curry-assignable types are preserved by the encoding.