George Eleftherakis

Communicating X-machines: a practical approach for formal and modular specification of large systems

Abstract An X-machine is a general computational machine that can model: (a) non-trivial data structures as a typed memory tuple and (b) the dynamic part of a system by employing transitions, which are not labelled with simple inputs but with functions that operate on inputs and memory values. The X-machine formal method is valuable to software engineers since it is rather intuitive, while at the same time formal descriptions of data types and functions can be written in any known mathematical notation. These differences allow the X-machines to be more expressive and flexible than a Finite State Machine. In addition, a set of X-machines can be viewed as components, which communicate with each other in order to specify larger systems. This paper describes a methodology as well as an appropriate notation, namely X-machine Description Language (XMDL), for building communicating X-machines from existing stand-alone X-machine models. The proposed methodology is accompanied by an example model of a traffic light junction, which demonstrates the use of communicating X-machines towards the incremental modelling of large-scale systems. It is suggested that through XMDL, the practical development of such complex systems can be split into two separate activities: (a) the modelling of stand-alone X-machine components and (b) the description of the communication between these components. The approach is disciplined, practical, modular and general in the sense that it subsumes the existing methods for communicating X-machines.

Communicating X-machines: from theory to practice

Formal modeling of complex systems is a non-trivial task, especially if a formal method does not facilitate separate development of the components of a system.Th is paper describes a methodology of building communicating X-machines from existing stand-alone X-machine models and presents the theory that drives this methodology. An X-machine is a formal method that resembles a finite state machine but can model non-trivial data structures.T his is accomplished by incorporating a typed memory tuple into the model as well as transitions labeled with functions that operate on inputs and memory values. A set of X-machines can exchange messages with each other, thus building a communicating system model. Ho wever, existing communicating X-machines theories imply that the components of a communicating system should be built from scratch. We suggest that modeling of complex systems can be split into two separate and distinct activities: (a) the modeling of standalone X-machine components and (b) the description of the communication between these components.Th is approach is based on a different view of the theory of communicating X-machines and it leads towards disciplined, practical, and modular development.T he proposed methodology is accompanied by an example, which demonstrates the use of communicating X-machines towards the modeling of large-scale systems.

Simulation and verification of P systems through communicating X-machines

The aim of this paper is to prove the suitability of a parallel distributed computational model, communicating X-machines, to simulate in a natural way a well established model of molecular computation, P systems, and to present some further benefits of the approach allowing us to check for some formal properties. A set of rules to transform any P system with symbol-objects into a communicating X-machine model is presented and a variation of temporal logic for X-machines is briefly discussed, which facilitates model checking of desired properties of the system. Finally, the benefits resulting from the transformation are discussed.

Transforming communicating X-machines into P systems

Tissue P systems (tPS) represent a class of P systems in which cells are arranged in a graph rather than a hierarchical structure. On the other hand, communicating X-machines (XMs) are state-based machines, extended with a memory structure and transition functions instead of simple inputs, which communicate via message passing. One could use communicating XMs to create models built out of components in a rather intuitive way. There are investigations showing how various classes of P systems can be modelled as communicating XMs. In this paper, we define a set of principles to transform communicating XMs into tPS. We describe the rules that govern such transformations, present an example to demonstrate the feasibility of this approach and discuss ways to extend it to more general models, such as population P systems, which involve dynamic structures.

Architecting the IoT paradigm: a middleware for autonomous distributed sensor networks

Actualizing Internet of Things undoubtedly constitutes a major challenge of modern computing and is a promising next step in realizing the unification of all seamlessly interacting entities, either human users or participating machines, under a shared, coherent architecture. While it has now become common belief that the related solutions should be based on compatible network infrastructure employing widely accepted communication schemes, the specifics of the intermediate system that would act as global interface for all involved “things” are yet to be determined. A rising trend to define such machine-based entities is through cyber-physical systems, in terms of collaborating elements with physical input and output. Certainly, sensor networks constitute the most representative realization of such systems. Taking these issues and opportunities under consideration, this work proposes a bioinspired distributed architecture for an Internet of Things that exhibits self-organization properties to enable efficient interaction between entities modeled as cyber-physical systems, mainly focusing on sensor networks. Furthermore, a middleware has been implemented according to the proposed architecture, which serves the role of the backbone of this network as a multiagent and autonomous distributed system. The evaluation results demonstrate the self-optimization properties of the introduced scheme and indicate global network convergence.

Evaluation of a selective distributed discovery strategy in a fully decentralized biologically inspired environment

The increased demand and complexity of services operating within open distributed environments has emphasized the need for systems that are adaptive, self-organizing and more robust. In order to address these issues some agent oriented approaches have adopted ideas from natural systems as possible solutions. The introduction of biological properties, especially birth and death of agents as expected events, generates an extremely dynamic environment where it is difficult to maintain the overall connectivity of the overlay network and facilitate efficient discovery processes. In this paper we evaluate the performance of a selective discovery mechanism in a distributed bio-inspired multi-agent community through a simulation study. The primary focus of the study is on the impacts which death and (sexual/asexual) reproduction events have on the effectiveness of the discovery process in different overlay networks.

Formal Verification of Generalised State Machines

The demand for more complex software is constantly increasing while at the same time the need for reliability leads modern software engineering to use more formally based development techniques. One of the most successfully employed formalisms to address the reliability issue were Finite State Machines (FSM) but they are too simple to capture the modelling needs of modern software that normally require manipulation of non-trivial data structures. X-machines is a formal method that provides such a data structure in form of a memory. On the other hand, FSM models are suitable for verification through model checking, i.e. to prove that certain properties are satisfied by a system model. However, with existing logics, it is obscure how one can describe properties that refer to the memory structure of an X-machine. This paper describes how a new logic, namely XmCTL, which extends temporal logic with memory quantifiers, facilitates model checking of X-machine models. XmCTL is defined and its use is demonstrated through the verification of a steam-boiler system which acts as a case study for our contribution.

Transforming State-Based Models to P Systems Models in Practice

We present an automatic practical transformation of Communicating X-machines to Population P Systems. The resulting compiler is able to take as input a Communicating X-machine model written in an appropriately designed language (XMDL) and produce a Population P System in another notation (PPSDL). The latter contains only transformation and communication rules. However, the user can further enhance the models with more rules that deal with the reconfiguration of structure of the network of cells. XMDL, PPSDL and their accompanied compilers and animators are briefly presented. The principles of transformations and the transformation templates of the compiler are discussed. We use an example model of a biological system, namely an ant colony, to demonstrate the usefulness of this approach.

Secure Judicial Communication Exchange Using Soft-computing Methods and Biometric Authentication

This paper describes how “Computer supported cooperative work”, coped with security technologies and advanced knowledge management techniques, can support the penal judicial activities, in particular national and trans-national investigations phases when different judicial system have to cooperate together. Increase of illegal immigration, trafficking of drugs, weapons and human beings, and the advent of terrorism, made necessary a stronger judicial collaboration between States. J-WeB project (http://www.jweb-net.com/), financially supported by the European Union under the FP6 – Information Society Technologies Programme, is designing and developing an innovative judicial cooperation environment capable to enable an effective judicial cooperation during cross-border criminal investigations carried out between EU and Countries of enlarging Europe, having the Italian and Montenegrin Ministries of Justice as partners. In order to reach a higher security level, an additional biometric identification system is integrated in the security environment.

Emergent Distributed Bio-organization: A Framework for Achieving Emergent Properties in Unstructured Distributed Systems

Distributed systems are particularly well suited to hosting emergent phenomena, especially when individual nodes possess a high degree of autonomy and the overall control tends to be decentralized. Introducing novel bio-inspired behaviours and interactions among individual nodes and the environment as a means of engineering desirable behaviours, could greatly assist with managing the complexity inherent to artificial distributed systems. The paper details the Emergent Distributed Bio-Organization (EDBO) as an abstract distributed system model aiming to engineer emergent properties at the macroscopic level. EDBO was designed to be suitable as a starting point in the design of a specific class of problems of real-world distributed systems. A thorough discussion justifies why the proposed bio-inspired properties planted into the model, could potentially allow for the desired behaviours to emerge.