Notion Of Behavioural Equivalence Research Articles

A Calculus of Mobility and Communication for Ubiquitous Computing

We propose a Calculus of Mobility and Communication (CMC) for the modelling of mobility, communication and context-awareness in the setting of ubiquitous computing. CMC is an ambient calculus with the in and out capabilities of Cardelli and Gordon's Mobile Ambients. The calculus has a new form of global communication similar to that in Milner's CCS. In CMC an ambient is tagged with a set of ports that agents executing inside the ambient are allowed to communicate on. It also has a new context-awareness feature that allows ambients to query their location. We present reduction semantics and labelled transition system semantics of CMC and prove that the semantics coincide. A new notion of behavioural equivalence is given by defining capability barbed bisimulation and congruence which is proved to coincide with barbed bisimulation congruence. The expressiveness of the calculus is illustrated by two case studies.

Exact fluid lumpability in Markovian process algebra

Quantitative analysis by means of discrete-state stochastic processes is hindered by the well-known phenomenon of state-space explosion, whereby the size of the state space may have an exponential growth with the number of agents of the system under scrutiny. When the stochastic process underlies a Markovian process algebra model, this problem may be alleviated by suitable notions of behavioural equivalence that induce lumping at the underlying continuous-time Markov chain, establishing an exact relation between a potentially much smaller aggregated chain and the original one. For the analysis of massively parallel systems, however, lumping techniques may not be sufficient to yield a computationally tractable problem. Recently, much work has been directed towards forms of fluid techniques that provide a set of ordinary differential equations (ODEs) approximating the expected path of the stochastic process. Unfortunately, even fluid models of realistic systems may be too large for feasible analysis. This paper studies a behavioural relation for process algebra with fluid semantics, called projected label equivalence, which is shown to yield an exactly fluid lumpable model, i.e., an aggregated ODE system which can be related to the original one without any loss of information. Project label equivalence relates sequential components of a process term. In general, for any two sequential components that are related in the fluid sense, nothing can be said about their relationship from the stochastic viewpoint. We define and study a notion of well-posedness which allows us to relate fluid lumpability to the stochastic notion of semi-isomorphism, which is a weaker version of the common notion of isomorphism between the doubly labelled transition systems at the basis of the Markovian interpretation.

Meta SOS - A Maude Based SOS Meta-Theory Framework

Meta SOS is a software framework designed to integrate the results from the meta-theory of structural operational semantics (SOS). These results include deriving semantic properties of language constructs just by syntactically analyzing their rule-based definition, as well as automatically deriving sound and ground-complete axiomatizations for languages, when considering a notion of behavioural equivalence. This paper describes the Meta SOS framework by blending aspects from the meta-theory of SOS, details on their implementation in Maude, and running examples.

TCTL-preserving translations from timed-arc Petri nets to networks of timed automata

We present a framework for TCTL-preserving translations between time-dependent modeling formalisms. The framework guarantees that once the original and the translated system are in one-by-many correspondence relation (a notion of behavioral equivalence between timed transition systems) then TCTL properties of the original system can be transformed too while preserving the verification answers. We demonstrate the usability of the technique on two reductions from bounded timed-arc Petri nets to networks for timed automata, providing unified proofs of the translations implemented in the verification tool TAPAAL. We evaluate the efficiency of the approach on a number of experiments: alternating bit protocol, Fischer's protocol, Lynch–Shavit protocol, MPEG-2 encoder, engine workshop and medical workflow. The results are encouraging and confirm the practical applicability of the approach.

Generalizing determinization from automata to coalgebras

The powerset construction is a standard method for converting a nondeterministic automaton into a deterministic one recognizing the same language. In this paper, we lift the powerset construction from automata to the more general framework of coalgebras with structured state spaces. Coalgebra is an abstract framework for the uniform study of different kinds of dynamical systems. An endofunctor F determines both the type of systems (F-coalgebras) and a notion of behavioural equivalence (~_F) amongst them. Many types of transition systems and their equivalences can be captured by a functor F. For example, for deterministic automata the derived equivalence is language equivalence, while for non-deterministic automata it is ordinary bisimilarity. We give several examples of applications of our generalized determinization construction, including partial Mealy machines, (structured) Moore automata, Rabin probabilistic automata, and, somewhat surprisingly, even pushdown automata. To further witness the generality of the approach we show how to characterize coalgebraically several equivalences which have been object of interest in the concurrency community, such as failure or ready semantics.

Structural non-interference in elementary and trace nets

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.

ONTOLOGY- AND BEHAVIOR-AWARE DISCOVERY OF WEB SERVICE COMPOSITIONS

Web service discovery is one of the key issues in the emerging area of Service-oriented Computing. In this paper, we present a complete composition-oriented, ontology-based methodology for discovering semantic Web services, which exploits functional and behavioral properties contained in OWL-S service advertisements to satisfy functional and behavioral client queries. To this aim, we build on top of the results contained in two recent articles, where we presented (1) a suitable data structure (viz. a dependency hypergraph) to collect functional information of services, and (2) a suitable notion of behavioral equivalence for Web services. We also discuss the architecture and the main implementation choices of the matchmaking system applying such a methodology.

Classification of security properties in a Linda-like process algebra

We provide a classification of noninterference-based security properties for the formal analysis of secure information flow in concurrent and distributed systems. This is done in the setting of a process algebra modeling some Linda coordination primitives (asynchronous communication and read operation). For this purpose, we define relaxed notions of behavioural equivalence that take into account the observational power of the external observer. The resulting taxonomy is compared with analogous security definitions based on synchronous communication models, thus emphasizing the influence of the Linda coordination model upon the expressivity of the security properties, by giving a new intuition to the relative merits.