Event-based systems are developed and used to integrate components in loosely coupled systems. Research and product development focused so far on e#ciency issues but neglected methodological support to build such systems. In this article, the modular design and implementation of an event system is presented which supports scopes and event mappings, two new and powerful structuring methods that facilitate engineering and coordination of components in event-based systems. We give a

We present an evaluation of advanced routing algorithms for content-based publish/subscribe systems that focuses on the inherent characteristics of routing algorithms (routing table sizes and filter forwarding overhead) instead of system-specific parameters (CPU load etc.). The evaluation is based on a working prototype instead of simulations and compares several routing algorithms to each other. Moreover, the effects of locality among the interests of the consumers are investigated. The results offer new insights into the behavior of content-based routing algorithms: Firstly, advanced routing algorithms can be considered mandatory in large-scale publish/subscribe systems. Secondly, the use of advertisements considerably improves the scalability. Thirdly, advanced routing algorithms operate efficiently in more dynamic environments than was previously thought. Finally, the good behavior of the algorithms even improves if the interests of the consumers are not evenly distributed, which can be expected in practice.

Achieving availability and scalability while providing service guarantees such as in-order, gapless delivery is essential for deploying publish/subscribe messaging middleware in wide area networks. Scalability often requires a publish/subscribe system to propagate subscription information and perform content matching across the network. Existing subscription propagation algorithms do not support in-order, gapless delivery in a redundant overlay network. This paper

Content-based publish/subscribe systems are usually implemented as a network of brokers that collaboratively route messages from information providers to consumers. A major challenge of such middleware infrastructures is their reliability and their ability to cope with failures in the system. In this paper, we present the architecture of the XNET XML content network and we detail the mechanisms that we implemented to gracefully handle failures and maintain the system state consistent with the consumer population at all times. In particular, we propose several approaches to fault tolerance so that our system can recover from various types of router and link failures. We analyze the efficiency of our techniques in a large scale experimental deployment on the PlanetLab testbed. We show that XNET does not only offer good performance and scalability with large consumer populations under normal operation, but can also quickly recover from system failures.

Content based publish-subscribe systems are being increasingly used to deliver information in large distributed environments. Subscription covering is an effective way to reduce the complexity of content-based routing and avoid unnecessary proliferation of subscriptions throughout the system. Although covering detection has been implemented in current systems, their efficient implementation has not been systematically studied so far. In this paper, we propose a general framework for covering detection and for maintaining covering relationships. We formalize the interaction between the above two tasks and show that a simple heuristic provides a 2-approximation algorithm for optimizing the number of covering queries on average. We also present efficient indexing schemes for covering queries resulting from range-based numeric subscriptions. We formulate this as a multidimensional rangesearch problem and explore the use of two well-known spatial indexes, k-d tree and space filling curve. Experimental results demonstrate that the proposed indexing schemes offer significant performance gains.

this paper. This way, publishers and subscribers use a common semantic level of subscription

Abstract. Component-based architectures are the traditional approach to reconcile application specific optimization with reusable abstractions in sensor networks. However, they frequently overwhelm the application designer with the range of choices in component selection and composition. We introduce a component framework that reduces this complexity. It provides a well-defined content-based publish/subscribe service, but allows the application designer to adapt the service by making orthogonal choices about: (1) the communication protocol components for subscription and notification delivery, (2) the supported data attributes and (3) a set of service extension components. We present TinyCOPS, our implementation of the framework in TinyOS 2.0, and demonstrate its advantages by showing experimental results for different application configurations on two sensor node platforms in a large-scale indoor testbed. 1

Abstract. Publish/subscribe middleware provides efficient support for loosely coupled communication in distributed systems. A number of different distributed message-filtering algorithms have been proposed. So far, a systematic comparison and analysis of these filter algorithms is still missing. This paper proposes a classification scheme for distributed filter algorithms that supports the theoretical and practical analysis of these algorithms. We present a first cut theoretical evaluation and a subsequent practical evaluation of promising candidate algorithms. Factors that are considered include the characteristics of the underlying network and application-related constraints. Based on the findings of these evaluations, we conclude with a summary of the strengths and weaknesses of the algorithms that we have studied. 1

We consider a problem that arises during the propagation of subscriptions in a content-based publish-subscribe system. Subscription covering is a promising optimization that reduces the number of subscriptions propagated, and hence the size of routing tables in a content-based publish-subscribe system. However, detecting covering relationships among subscriptions can be an expensive computational task that potentially reduces the utility of covering as an optimization. We introduce an alternate approach approximate subscription covering, which provide much of the benefits of subscription covering at a fraction of its cost. By forgoing an exhaustive search for covering subscriptions in favor of an approximate search, it is shown that the time complexity of covering detection can be dramatically reduced. The trade off between efficiency of covering detection and the approximation error is demonstrated through the analysis of indexes for multi-attribute subscriptions based on space filling curves. 1

The event-based approach is well suited for integrating autonomous components or applications into complex systems by means of exchanging events. Event-based systems need an event dissemination mechanism to deliver relevant events to interested consumers. The publish/subscribe interaction paradigm has been gaining relevance in this context. One of the main characteristics of publish/subscribe systems is that they decouple producers and consumers so that they can remain unknown to each other. Therefore, the consideration of data heterogeneity issues is fundamental. However, most pub/sub notification services do not support the interaction among heterogeneous event producers and consumers. In this paper we describe the concept-based approach as a high-level dissemination mechanism for distributed and heterogeneous event-based applications. It enhances the notification service by enabling it to pass semantic information across component, institutional or cultural boundaries. It provides a high level abstraction for a meaningful exchange of data within the pub/sub interaction paradigm. 1.