Composing distributed systems: overcoming the interoperability challenge

Software systems are increasingly composed of independently-developed components, which are often systems by their own. This composition is possible only if the components are interoperable, i.e., are able to work together in order to achieve some user task(s). However, interoperability is often hampered by the differences in the data types, communication protocols, and middleware technologies used by the components involved. In order to enable components to interoperate despite these differences, mediators that perform the necessary data translations and coordinate the components' behaviours appropriately, have been introduced. Still, interoperability remains a critical challenge for today's and even more tomorrow's distributed systems that are highly heterogeneous and dynamic. This chapter introduces the fundamental principles and solutions underlaying interoperability in software systems with a special focus on protocols. First, we take a software architecture perspective and present the fundamentals for reasoning about interoperability and bring out mediators as a key solution to achieve protocol interoperability. Then, we review the solutions proposed for the implementation, synthesis, and dynamic deployment of mediators. We show how these solutions still fall short in automatically solving the interoperability problem in the context of systems of systems. This leads us to present the solution elaborated in the context of the European Connect project, which revolves around the notion of emergent middleware, whereby mediators are synthesised on the fly

Automated synthesis of mediators to support component interoperability

Interoperability is a major concern for the software engineering field, given the increasing need to compose components dynamically and seamlessly. This dynamic composition is often hampered by differences in the interfaces and behaviours of independently-developed components. To address these differences without changing the components, mediators that systematically enforce interoperability between functionally-compatible components by mapping their interfaces and coordinating their behaviours are required. Existing approaches to mediator synthesis assume that an interface mapping is provided which specifies the correspondence between the operations and data of the components at hand. In this paper, we present an approach based on ontology reasoning and constraint programming in order to infer mappings between components' interfaces automatically. These mappings guarantee semantic compatibility between the operations and data of the interfaces. Then, we analyse the behaviours of components in order to synthesise, if possible, a mediator that coordinates the computed mappings so as to make the components interact properly. Our approach is formally-grounded to ensure the correctness of the synthesised mediator. We demonstrate the validity of our approach by implementing the MICS (Mediator synthesIs to Connect Components) tool and experimenting it with various real-world case studies

Dynamic decision networks for decision-making in self-adaptive systems: a case study

Bayesian decision theory is increasingly applied to support decision-making processes under environmental variability and uncertainty. Researchers from application areas like psychology and biomedicine have applied these techniques successfully. However, in the area of software engineering and specifically in the area of self-adaptive systems (SASs), little progress has been made in the application of Bayesian decision theory. We believe that techniques based on Bayesian Networks (BNs) are useful for systems that dynamically adapt themselves at runtime to a changing environment, which is usually uncertain. In this paper, we discuss the case for the use of BNs, specifically Dynamic Decision Networks (DDNs), to support the decision-making of self-adaptive systems. We present how such a probabilistic model can be used to support the decision-making in SASs and justify its applicability. We have applied our DDN-based approach to the case of an adaptive remote data mirroring system. We discuss results, implications and potential benefits of the DDN to enhance the development and operation of self-adaptive systems, by providing mechanisms to cope with uncertainty and automatically make the best decision

A Security Supervision System for Hybrid Networks

The traditional way of protecting networks and applications with e.g., firewalls and encryption, is no longer sufficient to protect effectively emerging hybrid wired-cum-wireless networks including ad hoc networks. Intrusion detection mechanisms should be coupled with preventive measures so as to identify unauthorised abuses. To this end, we propose a novel Hybrid Distributed Security Operation Center (HDSOC) which collects logs that are generated by any application/service, layer of the protocol stack or resource (e.g., router), providing a global view of the supervised system based on which complex and distributed intrusions can be detected. Our HDSOC further (i) distributes its capabilities and (ii) provides extensive coordination capabilities for guarantying that both the networks and the HDSOC components do not constitute isolated entities largely unaware of each others

Layered Connectors: Revisiting the Formal Basis of Architectural Connection for Complex Distributed Systems

International audienceThe complex distributed systems of nowadays require the dynamic composition of multiple components, which are autonomous and so complex that they can be considered as systems in themselves. These components often use different application protocols and are implemented on top of heterogeneous middleware, which hamper their successful interaction. The explicit and rigorous description and analysis of components interaction is essential in order to enable the dynamic composition of these components. In this paper, we propose a formal approach to represent and reason about interactions between components using layered connectors. Layered connectors describe components interaction at both the application and middleware layers and make explicit the role of middleware in the realisation of this interaction. We provide formal semantics of layered connectors and present an approach for the synthesis of layered connectors in order to enable the dynamic composition of highly heterogeneous components. We validate our approach through a case study in the area of collaborative emergency management

Dioptase: a distributed data streaming middleware for the future web of things

International audienceThe Internet of Things (IoT) is a promising concept toward pervasive computing as it may radically change the way people interact with the physical world, by connecting sensors to the Internet and, at a higher level, to the Web, thereby enacting a Web of Things (WoT). One of the challenges raised by the WoT is the in-network continuous processing of data streams presented by Things, which must be investigated urgently because it affects the future data models of the IoT, and is critical regarding the scalability and the sustainability required by the IoT. This cross-cutting concern has been previously studied in the context of Wireless Sensor Networks (WSN) given the focus on the acquisition and in-network processing of sensed data. However, proposed solutions feature various proprietary and highly specialized technologies that are difficult to integrate and complex to use, which represents a hurdle to their wide deployment. At the other end of the spectrum, cloud-based solutions introduce a too high energy cost for the envisioned IoT scale, considering the energy cost of communication over computation. There is thus a need for a distributed middleware solution for data stream management that leverages existing WSN work, while integrating it with today's Web technologies in order to support the required flexibility and the interoperability of the IoT.Toward that goal, this paper introduces Dioptase, a lightweight Data Stream Management System for the WoT, which aims to integrate the Things and their streams into today's Web by presenting sensors and actuators as Web services. The middleware specifically provides a way to describe complex fully-distributed stream-based mashups and to deploy them dynamically, at any time, as task graphs, over available Things of the network, including resource-constrained ones

From Task Graphs to Concrete Actions: A New Task Mapping Algorithm for the Future Internet of Things

International audienceTask mapping, which basically consists of mapping a set of tasks onto a set of nodes, is a well-known problem in distributed computing research. As a particular case of distributed systems, the Internet of Things (IoT) poses a set of renewed challenges, because of its scale, heterogeneity and properties traditionally associated with wireless sensor networks (WSN), shared sensing, continous processing and real time computing. To handle IoT features, we present a formalization of the task mapping problem that captures the varying consumption of resources and various constraints (location, capabilities, QoS) in order to compute a mapping that guarantees the lifetime of the concurrent tasks inside the network and the fair allocation of tasks among the nodes. It results in a binary programming problem for which we provide an efficient heuristic that allows its resolution in polynomial time. Our experiments show that our heuristic: (i) gives solutions that are close to optimal and (ii) can be implemented on reasonably powerful Things and performed directly within the network, without requiring any centralized infrastructure

An incentive compatible reputation mechanism for ubiquitous computing environments

International audienceThe vision of ubiquitous computing is becoming a reality thanks to the advent of portable devices and the advances in wireless networking technologies. It aims to facilitate user tasks through seamless utilization of services available in the surrounding environments. In such distributed environments featuring openness, interactions, especially service provision and consumption, between entities that are unknown or barely known to each other, are commonplace. Trust management through reputation mechanism to facilitate such interactions is recognized as an important element of ubiquitous computing. It is, however, faced by the problems of how to stimulate reputation information sharing and honest recommendation elicitation. We present in this paper an incentive compatible reputation mechanism to facilitate the trustworthiness evaluation in ubiquitous computing environments. It is based on probability theory and supports reputation evolution and propagation. Our reputation mechanism not only shows robustness against lies, but also stimulates honest and active recommendations. The latter is realized by ensuring that active and honest recommenders, compared to inactive or dishonest ones, can elicit the most honest (helpful) recommendations and thus suffer the least number of wrong trust decisions, as validated by simulation based evaluation

La puissance du crowdsensing au service de la durée de vie des réseaux IoT urbains

International audienceLe déploiement à grande échelle d'infrastructures de capteurs dans nos villes permet une meilleure gestion de l'espace urbain en offrant de nouvelles applications telles que la surveillance de la pollution, la gestion de l'énergie et des déchets, etc. En raison de contraintes environnementales, les capteurs sont souvent alimentés par pile. L'utilisation d'une communication convergecast réduit considérablement la durée de vie du réseau IoT urbain. Nous proposons donc d'équilibrer l'acheminement du trafic à l'intérieur du réseau pour mieux répartir la consommation d'énergie. Nous définissons un programme linéaire qui calcule un routage maximisant la durée de vie des infrastructures IoT. En outre, nous pensons que le réseau IoT urbain doit tirer parti de la puissance de la foule, ce qui conduit à combiner l'infrastructure avec les capacités de détection des smartphones des citoyens. Nous intégrons le déchargement d'une partie du trafic généré par l'infrastructure fixe vers des dispositifs mobiles de crowdsensing. Nous mettons en évidence les principales caractéristiques de cette coopération. L'évaluation de notre solution sur une topologie réaliste montre que nous sommes capables d'augmenter d'un facteur 7 la durée de vie de l'infrastructure IoT urbaine

CONNECT: Emergent Connectors for Eternal Software Intensive Networked Systems

International audienceThe CONNECT Integrated Project aims at dropping the interoperability barrier by adopting a revolutionary approach to the seamless networking of digital systems, that is, synthesizing on the fly the connectors via which networked systems communicate. CONNECT enables the dynamic synthesis of CONNECTors by introducing a formal foundation for connectors, which allows learning, reasoning about and adapting the interaction behavior of networked systems