Design and Implementation of Dynamically Evolving Ensembles with the HELENA Framework

Abstract-Ensembles are collections of autonomic entities which collaborate to perform certain tasks. They show typically a complex dynamic behavior which is difficult to implement with state of the art development techniques. In this paper, we present a systematic methodology for the design and implementation of ensemble-based systems which goes beyond component-based development. A conceptual key point of our approach (elaborated i

Helena

Ensemble-based systems are software-intensive systems consisting of large numbers of components which can dynamically form goal-oriented communication groups. The goal of an ensemble is usually achieved through interaction of some components, but the contributing components may simultaneously participate in several collaborations. With standard component-based techniques, such systems can only be described by a complex model specifying all ensembles and participants at the same time. Thus, ensemble-based systems lack a development methodology which particularly addresses the dynamic formation and concurrency of ensembles as well as transparency of participants. This thesis proposes the Helena development methodology. It slices an ensemble-based system in two dimensions: Each kind of ensemble is considered separately. This allows the developer to focus on the relevant parts of the system only and abstract away those parts which are non-essential to the current ensemble. Furthermore, an ensemble itself is not defined solely in terms of participating components, but in terms of roles which components adopt in that ensemble. A role is the logical entity needed to contribute to the ensemble while a component provides the technical functionalities to actually execute a role. By simultaneously adopting several roles, a component can concurrently participate in several ensembles. Helena addresses the particular challenges of ensemble-based systems in the main development phases: The domain of an ensemble-based system is described as an ensemble structure of roles built on top of a component-based platform. Based on the ensemble structure, the goals of ensembles are specified as linear temporal logic formulae. With these goals in mind, the dynamic behavior of the system is designed as a set of role behaviors. To show that the ensemble participants actually achieve the global goals of the ensemble by collaboratively executing the specified behaviors, the Helena model is verified against its goals with the model-checker Spin. For that, we provide a translation of Helena models to Promela, the input language of Spin, which is proven semantically correct for a kernel part of Helena. Finally, we provide the Java framework jHelena which realizes all Helena concepts in Java. By implementing a Helena model with this framework, Helena models can be executed according to the formal Helena semantics. To support all activities of the Helena development methodology, we provide the Helena workbench as a tool for specification and automated verification and code generation. The general applicability of Helena is backed by a case study of a larger software system, the Science Cloud Platform. Helena is able to capture, verify and implement the main characteristics of the system. Looking at Helena from a different angle shows that the Helena idea of roles is also well-suited to realize adaptive systems changing their behavioral modes based on perceptions. We extend the Helena development methodology to adaptive systems and illustrate its applicability at an adaptive robotic search-and-rescue example

Helena

Ensemble-based systems are software-intensive systems consisting of large numbers of components which can dynamically form goal-oriented communication groups. The goal of an ensemble is usually achieved through interaction of some components, but the contributing components may simultaneously participate in several collaborations. With standard component-based techniques, such systems can only be described by a complex model specifying all ensembles and participants at the same time. Thus, ensemble-based systems lack a development methodology which particularly addresses the dynamic formation and concurrency of ensembles as well as transparency of participants. This thesis proposes the Helena development methodology. It slices an ensemble-based system in two dimensions: Each kind of ensemble is considered separately. This allows the developer to focus on the relevant parts of the system only and abstract away those parts which are non-essential to the current ensemble. Furthermore, an ensemble itself is not defined solely in terms of participating components, but in terms of roles which components adopt in that ensemble. A role is the logical entity needed to contribute to the ensemble while a component provides the technical functionalities to actually execute a role. By simultaneously adopting several roles, a component can concurrently participate in several ensembles. Helena addresses the particular challenges of ensemble-based systems in the main development phases: The domain of an ensemble-based system is described as an ensemble structure of roles built on top of a component-based platform. Based on the ensemble structure, the goals of ensembles are specified as linear temporal logic formulae. With these goals in mind, the dynamic behavior of the system is designed as a set of role behaviors. To show that the ensemble participants actually achieve the global goals of the ensemble by collaboratively executing the specified behaviors, the Helena model is verified against its goals with the model-checker Spin. For that, we provide a translation of Helena models to Promela, the input language of Spin, which is proven semantically correct for a kernel part of Helena. Finally, we provide the Java framework jHelena which realizes all Helena concepts in Java. By implementing a Helena model with this framework, Helena models can be executed according to the formal Helena semantics. To support all activities of the Helena development methodology, we provide the Helena workbench as a tool for specification and automated verification and code generation. The general applicability of Helena is backed by a case study of a larger software system, the Science Cloud Platform. Helena is able to capture, verify and implement the main characteristics of the system. Looking at Helena from a different angle shows that the Helena idea of roles is also well-suited to realize adaptive systems changing their behavioral modes based on perceptions. We extend the Helena development methodology to adaptive systems and illustrate its applicability at an adaptive robotic search-and-rescue example

On-Demand Composition of Smart Service Systems in Decentralized Environments

The increasing number of smart systems inevitably leads to a huge number of systems that potentially provide independently designed, autonomously operating services. In near-future smart computing systems, such as smart cities, smart grids or smart mobility, independently developed and heterogeneous services need to be dynamically interconnected in order to develop their full potential in a rather complex collaboration with others. Since the services are developed independently, it is challenging to integrate them on-the-fly at run time. Due to the increasing degree of distribution, such systems operate in a decentralized and volatile environment, where central management is infeasible. Conversely, the increasing computational power of such systems also supersedes the need for central management. The four identified key problems of adaptable, collaborative Smart Service Systems are on-demand composition of complex service structures in decentralized environments, the absence of a comprehensive, serendipity-aware specification, a discontinuity from design-time specification to run-time execution, and the lack of a development methodology that separates the development of a service from that of its role essential to a collaboration. This approach utilizes role-based models, which have a collaborative nature, for automated, on-demand service composition. A rigorous two-phase development methodology is proposed in order to demarcate the development of the services from that of their role essential to a collaboration. Therein, a collaboration designer specifies the collaboration including its abstract functionality using the proposed role-based collaboration specification for Smart Service Systems. Thereof, a partial implementation is derived, which is complemented by services developed in the second phase. The proposed middleware architecture provides run-time support and bridges the gap between design and run time. It implements a protocol for coordinated, role-based composition and adaptation of Smart Service Systems. The approach is quantitatively and qualitatively evaluated by means of a case study and a performance evaluation in order to identify limitations of complex service structures and the trade-off of employing the concept of roles for composition and adaptation of Smart Service Systems.:1 Introduction 1.1 Motivation 1.2 Terminology 1.3 Problem Statement 1.4 Requirements Analysis 1.5 Research Questions and Hypothesis 1.6 Focus and Limitations 1.7 Outline 2 The Role Concept in Computer Science 2.1 What is a Role in Computer Science? 2.2 Roles in RoleDiSCo 3 State of the Art & Related Work 3.1 Role-based Modeling Abstractions for Software Systems 3.1.1 Classification 3.1.2 Approaches 3.1.3 Summary 3.2 Role-based Run-Time Systems 3.2.1 Classification 3.2.2 Approaches 3.2.3 Summary 3.3 Spontaneously Collaborating Run-Time Systems 3.3.1 Classification 3.3.2 Approaches 3.3.3 Summary 3.4 Summary 4 On-Demand Composition and Adaptation of Smart Service Systems 4.1 RoleDiSCo Development Methodology 4.1.1 Role-based Collaboration Specification for Smart Service Systems 4.1.2 Derived Partial Implementation 4.1.3 Player & Context Provision 4.2 RoleDiSCo Middleware Architecture for Smart Service Systems 4.2.1 Infrastructure Abstraction Layer 4.2.2 Context Management 4.2.3 Local Repositories & Knowledge 4.2.4 Discovery 4.2.5 Dispatcher 4.3 Coordinated Composition and Subsequent Adaptation 4.3.1 Initialization and Planning 4.3.2 Composition: Coordinating Subsystem 4.3.3 Composition: Non-Coordinating Subsystem 4.3.4 Competing Collaborations & Negotiation 4.3.5 Subsequent Adaptation 4.3.6 Terminating a Pervasive Collaboration 4.4 Summary 5 Implementing RoleDiSCo 5.1 RoleDiSCo Development Support 5.2 RoleDiSCo Middleware 5.2.1 Infrastructure Abstraction Layer 5.2.2 Knowledge Repositories and Local Class Discovery 5.2.3 Planner 6 Evaluation 6.1 Case Study: Distributed Slideshow 6.1.1 Scenario 6.1.2 Phase 1: Collaboration Design 6.1.3 Phase 2: Player Complementation 6.1.4 Coordinated Composition and Adaptation at Run Time 6.2 Runtime Evaluation 6.2.1 General Testbed Setup and Scenarios 6.2.2 Discovery Time 6.2.3 Composition Time 6.2.4 Discussion 6.3 The ›Role‹ of Roles 6.4 Summary 7 Conclusion 7.1 Summary 7.2 Research Results 7.3 Future Wor

From distributed coordination to field calculus and aggregate computing

open6siThis work has been partially supported by: EU Horizon 2020 project HyVar (www.hyvar-project .eu), GA No. 644298; ICT COST Action IC1402 ARVI (www.cost -arvi .eu); Ateneo/CSP D16D15000360005 project RunVar (runvar-project.di.unito.it).Aggregate computing is an emerging approach to the engineering of complex coordination for distributed systems, based on viewing system interactions in terms of information propagating through collectives of devices, rather than in terms of individual devices and their interaction with their peers and environment. The foundation of this approach is the distillation of a number of prior approaches, both formal and pragmatic, proposed under the umbrella of field-based coordination, and culminating into the field calculus, a universal functional programming model for the specification and composition of collective behaviours with equivalent local and aggregate semantics. This foundation has been elaborated into a layered approach to engineering coordination of complex distributed systems, building up to pragmatic applications through intermediate layers encompassing reusable libraries of program components. Furthermore, some of these components are formally shown to satisfy formal properties like self-stabilisation, which transfer to whole application services by functional composition. In this survey, we trace the development and antecedents of field calculus, review the field calculus itself and the current state of aggregate computing theory and practice, and discuss a roadmap of current research directions with implications for the development of a broad range of distributed systems.embargoed_20210910Viroli, Mirko; Beal, Jacob; Damiani, Ferruccio; Audrito, Giorgio; Casadei, Roberto; Pianini, DaniloViroli, Mirko; Beal, Jacob; Damiani, Ferruccio; Audrito, Giorgio; Casadei, Roberto; Pianini, Danil

Context-based confidentiality analysis in dynamic Industry 4.0 scenarios

In Industry 4.0 environments highly dynamic and flexible access control strategies are needed. State of the art strategies are often not included in the modelling process but must be considered afterwards. This makes it very difficult to analyse the security properties of a system. In the framework of the Trust 4.0 project the confidentiality analysis tries to solve this problem using a context-based approach. Thus, there is a security model named context metamodel. Another important problem is that the transformation of an instance of a security model to a wide-spread access control standard is often not possible. This is also the case for the context metamodel. Moreover, another transformation which is very interesting to consider is one to an ensemble based component system which is also presented in the Trust 4.0 project. This thesis introduces an extension to the beforementioned context metamodel in order to add more extensibility to it. Furthermore, the thesis deals with the creation of a concept and an implementation of the transformations mentioned above. For that purpose, at first, the transformation to the attribute-based access control standard XACML is considered. Thereafter, the transformation from XACML to an ensemble based component system is covered. The evaluation indicated that the model can be used for use cases in Industry 4.0 scenarios. Moreover, it also indicated the transformations produce adequately accurate access policies. Furthermore, the scalability evaluation indicated linear runtime behaviour of the implementations of both transformations for respectively higher number of input contexts or XACML rules

Engineering Self-Adaptive Collective Processes for Cyber-Physical Ecosystems

The pervasiveness of computing and networking is creating significant opportunities for building valuable socio-technical systems. However, the scale, density, heterogeneity, interdependence, and QoS constraints of many target systems pose severe operational and engineering challenges. Beyond individual smart devices, cyber-physical collectives can provide services or solve complex problems by leveraging a “system effect” while coordinating and adapting to context or environment change. Understanding and building systems exhibiting collective intelligence and autonomic capabilities represent a prominent research goal, partly covered, e.g., by the field of collective adaptive systems. Therefore, drawing inspiration from and building on the long-time research activity on coordination, multi-agent systems, autonomic/self-* systems, spatial computing, and especially on the recent aggregate computing paradigm, this thesis investigates concepts, methods, and tools for the engineering of possibly large-scale, heterogeneous ensembles of situated components that should be able to operate, adapt and self-organise in a decentralised fashion. The primary contribution of this thesis consists of four main parts. First, we define and implement an aggregate programming language (ScaFi), internal to the mainstream Scala programming language, for describing collective adaptive behaviour, based on field calculi. Second, we conceive of a “dynamic collective computation” abstraction, also called aggregate process, formalised by an extension to the field calculus, and implemented in ScaFi. Third, we characterise and provide a proof-of-concept implementation of a middleware for aggregate computing that enables the development of aggregate systems according to multiple architectural styles. Fourth, we apply and evaluate aggregate computing techniques to edge computing scenarios, and characterise a design pattern, called Self-organising Coordination Regions (SCR), that supports adjustable, decentralised decision-making and activity in dynamic environments.Con lo sviluppo di informatica e intelligenza artificiale, la diffusione pervasiva di device computazionali e la crescente interconnessione tra elementi fisici e digitali, emergono innumerevoli opportunità per la costruzione di sistemi socio-tecnici di nuova generazione. Tuttavia, l'ingegneria di tali sistemi presenta notevoli sfide, data la loro complessità—si pensi ai livelli, scale, eterogeneità, e interdipendenze coinvolti. Oltre a dispositivi smart individuali, collettivi cyber-fisici possono fornire servizi o risolvere problemi complessi con un “effetto sistema” che emerge dalla coordinazione e l'adattamento di componenti fra loro, l'ambiente e il contesto. Comprendere e costruire sistemi in grado di esibire intelligenza collettiva e capacità autonomiche è un importante problema di ricerca studiato, ad esempio, nel campo dei sistemi collettivi adattativi. Perciò, traendo ispirazione e partendo dall'attività di ricerca su coordinazione, sistemi multiagente e self-*, modelli di computazione spazio-temporali e, specialmente, sul recente paradigma di programmazione aggregata, questa tesi tratta concetti, metodi, e strumenti per l'ingegneria di ensemble di elementi situati eterogenei che devono essere in grado di lavorare, adattarsi, e auto-organizzarsi in modo decentralizzato. Il contributo di questa tesi consiste in quattro parti principali. In primo luogo, viene definito e implementato un linguaggio di programmazione aggregata (ScaFi), interno al linguaggio Scala, per descrivere comportamenti collettivi e adattativi secondo l'approccio dei campi computazionali. In secondo luogo, si propone e caratterizza l'astrazione di processo aggregato per rappresentare computazioni collettive dinamiche concorrenti, formalizzata come estensione al field calculus e implementata in ScaFi. Inoltre, si analizza e implementa un prototipo di middleware per sistemi aggregati, in grado di supportare più stili architetturali. Infine, si applicano e valutano tecniche di programmazione aggregata in scenari di edge computing, e si propone un pattern, Self-Organising Coordination Regions, per supportare, in modo decentralizzato, attività decisionali e di regolazione in ambienti dinamici

Collective Adaptive Systems: Qualitative and Quantitative Modelling and Analysis (Dagstuhl Seminar 14512)

This report documents the program and the outcomes of Dagstuhl Seminar 14512 "Collective Adaptive Systems: Qualitative and Quantitative Modelling and Analysis". Besides presentations on current work in the area, the seminar focused on the following topics: (i) Modelling techniques and languages for collective adaptive systems based on the above formalisms. (ii) Verification of collective adaptive systems. (iii) Humans-in-the-loop in collective adaptive systems