Semantic-based policy engineering for autonomic systems

This paper presents some important directions in the use of ontology-based semantics in achieving the vision of Autonomic Communications. We examine the requirements of Autonomic Communication with a focus on the demanding needs of ubiquitous computing environments, with an emphasis on the requirements shared with Autonomic Computing. We observe that ontologies provide a strong mechanism for addressing the heterogeneity in user task requirements, managed resources, services and context. We then present two complimentary approaches that exploit ontology-based knowledge in support of autonomic communications: service-oriented models for policy engineering and dynamic semantic queries using content-based networks. The paper concludes with a discussion of the major research challenges such approaches raise

FAIDECS: Fair Decentralized Event Correlation

Part 5: Notification and StreamingInternational audienceMany distributed applications rely on event correlation. Such applications, when not built as ad-hoc solutions, typically rely on centralized correlators or on broker overlay networks. Centralized correlators constitute performance bottlenecks and single points of failure; straightforwardly duplicating them can hamper performance and cause processes interested in the same correlations to reach different outcomes. The latter problem can manifest also if broker overlays provide redundant paths to tolerate broker failures as events do not necessarily reach all processes via the same path and thus in the same order.This paper describes FAIDECS, a generic middleware system for fair decentralized correlation of events multicast among processes: processes with identical interests reach identical outcomes, and subsumption relationships among subscriptions are considered for respectively delivered composite events. Based on a generic subset of FAIDECS’s predicate language, we introduce properties for composite event deliveries in the presence of process failures and present novel decentralized algorithms implementing these properties. Our algorithms are compared under various workloads to solutions providing equivalent guarantees

Composite Subscriptions in Content-Based Publish/Subscribe Systems

Abstract. Distributed publish/subscribe systems are naturally suited for processing events in distributed systems. However, support for expressing patterns about distributed events and algorithms for detecting correlations among these events are still largely unexplored. Inspired from the requirements of decentralized, event-driven workflow processing, we design a subscription language for expressing correlations among distributed events. We illustrate the potential of our approach with a workflow management case study. The language is validated and implemented in PADRES. In this paper we present an overview of PADRES, highlighting some of its novel features, including the composite subscription language, the coordination patterns, the composite event detection algorithms, the rule-based router design, and a detailed case study illustrating the decentralized processing of workflows. Our experimental evaluation shows that rule-based brokers are a viable and powerful alternative to existing, special-purpose, content-based routing algorithms. The experiments also show that the use of composite subscriptions in PADRES significantly reduces the load on the network. Complex workflowscanbeprocessedinadecentralizedfashionwithagainof40% in message dissemination cost. All processing is realized entirely in the publish/subscribe paradigm.

Dependability and Performance Assessment of Dynamic CONNECTed Systems

Abstract. In this chapter we present approaches for analysis and monitoring of dependability and performance of Connected systems, and their combined usage. These approaches need to account for dynamicity and evolvability of Connected systems. In particular, the chapter covers the quantitative assessment of dependability and performance properties through a stochastic model-based approach: first an overview of dependability-related measurements and stochastic model-based approaches provides the necessary background. Then, our proposal in Connect of an automated and modular dependability analysis framework for dynamically Connected systems is described. This framework can be used off-line for system design (specifically, in Connect, for Connector synthesis), and on-line, to continuously assess system behaviour and detect possible issues arising at run-time. For the latter purpose, a generic, flexible and modular monitoring infrastructure has been developed. Monitoring is at the core of the Connect vision, in order to ensure run-time observation of specified quantitative properties and possibly trigger adequate reactions. We focus here on the interaction chain between monitoring and analysis, to allow for on-line continuous validation of specified dependability and performance properties. Illustrative examples of applications of analysis and monitoring are provided with reference to the Connect Terrorist Alert scenario.