Ambient Calculus Research Articles

A language for the execution of graded BDI agents

We are interested in the specification and deployment of multi-agent systems, and particularly we focus on the execution of agents. Along this research line, we have proposed a general model for graded BDI agents, specifying an architecture based on multi-context systems (MCSs) and able to deal with the environment uncertainty (via graded beliefs) and with graded mental proactive attitudes (via desires and intentions). These graded attitudes are represented using appropriate fuzzy modal logics. In this article, we cope with the operational semantics of this agent model. We present a Multi-context calculus, based on Ambient calculus, for the execution of MCSs with its corresponding semantics. This calculus is general enough to support different kinds of MCSs and particularly, we show how a graded BDI agent can be mapped into the language of the calculus.

프로세스 대수에서 이동성과 상호작용을 분석하기 위한 행위 온톨로지를 이용한 추상화 방법

분산 이동 실시간 시스템을 개발하기 위해 pi-Calculus, Mobile Ambients Calculus, Bigraph 등의 수많은 프로세스 대수가 존재한다. 하지만 시스템이 방대해지고 복잡해질수록 시스템을 구성하는 프로세스들의 통신과 이동 역시 방대해지고 복잡해지므로 프로세스 대수로 이를 이해하는데 어려움이 존재한다. 그러므로 방대하고 복잡한 시스템을 체계적으로 이해할 수 있는 방법이 필요하다. 본 논문에서는 방대하고 복잡한 시스템을 프로세스들의 통신과 이동의 순서화된 추상화 방법 즉, 계층적으로 구조화된 격자(Lattice)들의 형태인 프리즘(Prism)으로 다룬다. 이는 액티브 온톨로지(Active Ontology)에서 확장된 새로운 개념인 행위 온톨로지(Behavior Ontology)를 기반으로 한다. 프리즘은 시스템을 체계적으로 이해하기 위해 시스템을 계층적으로 구성된 행위적 속성을 지닌 격자들 관점에서 분석하는 것을 허용한다. 이러한 방법은 통신과 이동의 복잡함을 의미적이고 계층적으로 구성된 행위의 구조로 체계적으로 이해할 수 있게 한다. A number of process algebras have been proposed to develop distributed mobile real-time systems: pi-Calculus, Mobile Ambients Calculus, Bigraph, etc. However, as the systems get large and complex, the algebras become less suitable for understanding the interactions and mobility of the processes of the systems due to the size and complexity. Therefore it is necessary to handle the size and complexity for systematic understanding of the systems. This paper handles the size and complexity with a method of abstraction on sequences of interactions and movements of processes in the systems, which can be further organized in the form of hierarchically structured lattices, namely, Prism. The theoretical principle of the abstraction is based on a new concept of Behavior Ontology, which is extended from Active ontology. Prism allows the systems to be analyzed in the perspective of the lattices in Prism, which are characterized by the hierarchically organized behavioral properties of the developing systems, for systematic understanding the systems. In this way, the complexity of the interactions and the movements can be handled systematically in the semantically and hierarchically organized structure of the behavior.

A decentralised graphical implementation of mobile ambients

We present a graphical implementation for finite processes of the mobile ambients calculus. Our encoding uses unstructured (i.e., non-hierarchical) graphs and it is sound and complete with respect to the structural congruence of the calculus (i.e., two processes are equivalent iff mapped to isomorphic graphs). With respect to alternative proposals for the graphical implementation of mobile ambients, our encoding distinguishes the syntactic structure of a process from the activation order of its components. Our solution faithfully captures a basic feature of the calculus (ambients can be nested and reductions are propagated across the nesting) and it allows to model the reduction semantics via a graph transformation system containing just three rules.

Deriving structural labelled transitions for mobile ambients

We present a new labelled transition system ( lts) for the ambient calculus. Its most important property is that ordinary (strong) bisimulation coincides with (strong) contextual equivalence. The lts is the outcome of the authors’ ongoing work towards developing general techniques and systematic procedures for deriving ltss in the structural ( sos) style from the underlying reduction semantics and observability.

The Ambience of Ambience

The Ambience of Ambience

Abstract interpretation based verification of temporal properties for BioAmbients

This paper concerns the application of formal methods to biological systems, modeled specifically in BioAmbients, a variant of the Mobile Ambients calculus. Following the semantic-based approach of abstract interpretation, we define a new static analysis that computes an abstract transition system. Our analysis has two main advantages with respect to the analyses appearing in the literature: (i) it is able to address temporal properties which are more general than invariant properties; (ii) it supports, by means of a particular labeling discipline, the validation of systems where several copies of an ambient may appear. We also design new weaker and more efficient analyses by means of simple widening operators.

The Calculus of Context-aware Ambients

We present the Calculus of Context-aware Ambients ( CCA in short) for the modelling and verification of mobile systems that are context-aware. This process calculus is built upon the calculus of mobile ambients and introduces new constructs to enable ambients and processes to be aware of the environment in which they are being executed. This results in a powerful calculus where both mobility and context-awareness are first-class citizens. We present the syntax and a formal semantics of the calculus. We propose a new theory of equivalence of processes which allows the identification of systems that have the same context-aware behaviours. We prove that CCA encodes the π-calculus which is known to be a universal model of computation. Finally, we illustrate the pragmatics of the calculus through many examples and a real-world case study of a context-aware hospital bed.

On Barbs and Labels in Reactive Systems

Reactive systems (RSs) represent a meta-framework aimed at deriving behavioral congruences for those computational formalisms whose operational semantics is provided by reduction rules. RSs proved a flexible specification device, yet so far most of the efforts dealing with their behavioural semantics focused on idem pushouts (IPOs) and saturated (also known as dynamic) bisimulations. In this paper we introduce a novel, intermediate behavioural equivalence: L-bisimilarity, which is able to recast both its IPO and saturated counterparts. The equivalence is parametric with respect to a set L of RSs labels, and it is shown that under mild conditions on L it is indeed a congruence. Furthermore, L-bisimilarity can also recast the notion of barbed semantics for RSs, proposed by the same authors in a previous paper. In order to provide a suitable test-bed, we instantiate our proposal by addressing the semantics of (asynchronous) CCS and of the calculus of mobile ambients.

Ambient-PRISMA: Ambients in mobile aspect-oriented software architecture

This work presents an approach called Ambient-PRISMA for modelling and developing distributed and mobile applications. Ambient-PRISMA enriches an aspect-oriented software architectural approach called PRISMA with the ambient concept from Ambient Calculus. Ambients are introduced in PRISMA as specialized kinds of connectors that offer mobility services to architectural elements (components and connectors) and are able to coordinate a boundary, which models the notion of location. Mobility of architectural elements is supported by reconfiguring the software architecture. This paper presents a metamodel that introduces ambients to design aspect-oriented software architectural models for mobile systems. The design of models is performed using an Aspect-Oriented Architecture Description Language. A middleware called Ambient-PRISMANET which maps the metamodel to .NET technology and supports the distributed runtime environment needed for executing mobile applications is also presented. In addition, a CASE Tool which allows users to specify the aspect-oriented architectural models in a graphical way and generate .NET code is provided. In this way, we explain how Ambient-PRISMA follows Model Driven Engineering. An example of an auction system is used throughout the article to illustrate the work.

Hybrid logical analyses of the ambient calculus

In this paper, hybrid logic is used to formulate three control flow analyses for Mobile Ambients, a process calculus designed for modelling mobility. We show that hybrid logic is very well-suited to express the semantic structure of the ambient calculus and how features of hybrid logic can be exploited to reduce the “administrative overhead” of the analysis specification and thus simplify it. Finally, we use HyLoTab, a fully automated theorem prover for hybrid logic, both as a convenient platform for a prototype implementation as well as to formally prove the correctness of the analysis.

Deciding reachability problems in Turing-complete fragments of Mobile Ambients

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.

On Mobility and Communication

By imposing three semantic constraints on the π-calculus equipped with delayed input, we obtain a variant of the π-calculus. We prove that Hennessy and Riely's distributed π-calculus can be encoded into this new model, satisfying a full abstraction theorem, which means that one-dimensional mobility can be characterized by communication. We also discuss the difficulties of expressing two-dimensional mobility, the mechanism used by ambient calculi.

CoBiC: Context-dependent Bioambient Calculus

In biological phenomena like osmosis, the rate of flow of water molecules in or out of biological compartments depends on the solute concentration and on other forces, like hydrostatic pressure. A similar example is the passive transport of ions in and out the cell membrane. In this paper, we address the problem of faithfully modelling these kind of phenomena with an adequate process calculus. We enhance the ambient calculus stochastic semantics with functional rates, which are calculated by taking into account the volume of ambients and the surrounding environment. A model of osmosis in plant cells will be used as an example to show the new features of our calculus.

Mutual Mobile Membranes with Timers

A feature of current membrane systems is the fact that objects and membranes are persistent. However, this is not true in the real world. In fact, cells and intracellular proteins have a well-defined lifetime. Inspired from these biological facts, we define a model of systems of mobile membranes in which each membrane and each object has a timer representing their lifetime. We show that systems of mutual mobile membranes with and without timers have the same computational power. An encoding of timed safe mobile ambients into systems of mutual mobile membranes with timers offers a relationship between two formalisms used in describing biological systems.

Labelled Transitions for Mobile Ambients (As Synthesized via a Graphical Encoding)

The paper presents a case study on the synthesis of labelled transition systems (LTSs) for process calculi, choosing as testbed Cardelli and Gordon's Mobile Ambients (MAs). The proposal is based on a graphical encoding: each process is mapped into a graph equipped with suitable interfaces, such that the denotation is fully abstract with respect to the usual structural congruence. Graphs with interfaces are amenable to the synthesis mechanism proposed by Ehrig and König and based on borrowed contexts (BCs), an instance of relative pushouts, introduced by Leifer and Milner. The BC mechanism allows the effective construction of a LTS that has graphs with interfaces as both states and labels, and such that the associated bisimilarity is automatically a congruence. Our paper focuses on the analysis of a LTS over (processes as) graphs with interfaces, as distilled by exploiting the graphical encoding of MAs. In particular, we use the LTS on graphs to recover a suitable LTS directly defined over the structure of MAs processes.

Deciding Reachability in Mobile Ambients with Name Restriction

We investigate the reachability problem for fragments of the Mobile Ambients, a powerful model for distributed and mobile computation. By using a connection with associative-commutative term rewriting, we prove that reachability is decidable in the open-free fragment of pure Mobile Ambients with name restriction and weak reduction semantics. Processes in this model have three sources of infiniteness: depth of ambients, width of parallel composition, and number of restricted names. Our work extends similar results obtained for public fragments of Mobile Ambients.

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.

Reachability Analysis in BioAmbients

We rephrase results, previously proved by Busi and Zavattaro on Mobile Ambients, characterizing a fragment of BioAmbients –without restriction and merge– in which a generalized form of reachability turns out to be decidable.

Flow-sensitive type systems and the ambient calculus

The Ambient Calculus was developed by Cardelli and Gordon as a formal framework to study issues of mobility and migrant code. Numerous analyses have been developed for numerous variants of that calculus. We take up the challenge of developing, in a type-based setting, a relatively precise topology analysis for the original version of the calculus. To compensate for the lack of co-capabilities (an otherwise increasingly popular extension), the analysis is flow-sensitive, with the actions of processes being summarized by behaviors. A subject reduction property guarantees that for a well-typed process, the location of any ambient is included in what is predicted by its type; additionally it ensures that communicating subprocesses agree on their topic of conversation. Based on techniques borrowed from finite automata theory, type checking of type-annotated processes is decidable (though potentially exponential).

Separability in the Ambient Logic

The \it{Ambient Logic} (AL) has been proposed for expressing properties of process mobility in the calculus of Mobile Ambients (MA), and as a basis for query languages on semistructured data. We study some basic questions concerning the discriminating power of AL, focusing on the equivalence on processes induced by the logic $(=_L>)$. As underlying calculi besides MA we consider a subcalculus in which an image-finiteness condition holds and that we prove to be Turing complete. Synchronous variants of these calculi are studied as well. In these calculi, we provide two operational characterisations of $_=L$: a coinductive one (as a form of bisimilarity) and an inductive one (based on structual properties of processes). After showing $_=L$ to be stricly finer than barbed congruence, we establish axiomatisations of $_=L$ on the subcalculus of MA (both the asynchronous and the synchronous version), enabling us to relate $_=L$ to structural congruence. We also present some (un)decidability results that are related to the above separation properties for AL: the undecidability of $_=L$ on MA and its decidability on the subcalculus.