Efficient Probabilistic Subsumption Checking for Content-Based Publish/Subscribe Systems

Abstract. Efficient subsumption checking, deciding whether a subscription or publication is covered by a set of previously defined subscriptions, is of paramount importance for publish/subscribe systems. It provides the core system functionality—matching of publications to subscriber needs expressed as subscriptions—and additionally, reduces the overall system load and generated traffic since the covered subscriptions are not propagated in distributed environments. As the subsumption problem was shown previously to be co-NP complete and existing solutions typically apply pairwise comparisons to detect the subsumption relationship, we propose a ‘Monte Carlo type ’ probabilistic algorithm for the general subsumption problem. It determines whether a publication/subscription is covered by a disjunction of subscriptions in O(k md), wherek is the number of subscriptions, m is the number of distinct attributes in subscriptions, and d is the number of tests performed to answer a subsumption question. The probability of error is problem-specific and typically very small, and sets an upper bound on d. Our experimental results show significant gains in term of subscription set reduction which has favorable impact on the overall system performance as it reduces the total computational costs and networking traffic. Furthermore, the expected theoretical bounds underestimate algorithm performance because it performs much better in practice due to introduced optimizations, and is adequate for fast forwarding of subscriptions in case of high subscription rate.

Mobile Information Systems 3 (2007) 107-132 107 IOS Press High performance publish/subscribe middleware for mobile wireless networks

Abstract. Decoupling, flexible, scalable and asynchronous nature of publish/subscribe paradigms makes them a good choice for mobile wireless networks. However, our research shows that current implementations of publish/subscribe systems as well as the traditional solutions for extending publish/subscribe systems to the mobile domain do not perform well in highly mobile and unreliable wireless settings. We present semi-durable subscriptions, a technique that we have developed to overcome the challenges and the performance concerns publish/subscribe systems face in mobile wireless settings. We discuss the architecture of semi-durable subscriptions and study in detail the effect of various mobility parameters on the performance of semi-durable subscriptions to demonstrate their efficacy in mobile wireless settings. We also discuss system parameters for semi-durable subscriptions and with the help of experimental results demonstrate how these parameters can be controlled to configure a system according to a set of desired characteristics

Fast Probabilistic Subsumption Checking for Publish/Subscribe Systems

Efficient subsumption checking, deciding whether a subscription or publication is subsumed (covered) by a set of previously defined subscriptions, is of paramount importance for publish/subscribe systems. It provides the core system functionality, and additionally, reduces the overall system load and generated traffic in distributed environments. As the deterministic solution was shown previously to be co-NP complete and existing solutions typically employ costly pairwise comparisons to detect the subsumption relationship, we propose a probabilistic algorithm for the general subsumption problem. It efficiently determines whether a publication/subscription is covered by a disjunction of subscriptions in $O(k~m~d)$, where $k$ is the number of subscriptions, $m$ is the number of distinct attributes in subscriptions, and $d$ is the number of tests performed to answer a subsumption question. The probability of error is problem specific and typically very small, and determines an upper bound on $d$ in polynomial time prior to the algorithm execution. Our experimental results demonstrate the algorithm performs even better in practice due to introduced optimizations, and is adequate for fast forwarding of publications/subscriptions, especially in resource scarce environments, e.g. sensor networks

Evaluating Advanced Routing Algorithms for Content-Based Publish/Subscribe Systems

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

Trusted content-based publish/subscribe trees

Publish/Subscribe systems hold strong assumptions of the expected behaviour of clients and routers, as it is assumed they all abide by the matching and routing protocols. Assumptions of implicit trust between the components of the publish/subscribe infrastructure are acceptable where the underlying event distribution service is under the control of a single or multiple co-operating administrative entities and contracts between clients and these authorities exist, however there are application contexts where these presumptions do not hold. In such environments, such as ad hoc networks, there is the possibility of selfish and malicious behaviour that can lead to disruption of the routing and matching algorithms. The most commonly researched approach to security in publish/subscribe systems is role-based access control (RBAC). RBAC is suitable for ensuring confidentiality, but due to the assumption of strong identities associated with well defined roles and the absence of monitoring systems to allow for adaptable policies in response to the changing behaviour of clients, it is not appropriate for environments where: identities can not be assigned to roles in the absence of a trusted administrative entity; long-lived identities of entities do not exist; and where the threat model consists of highly adaptable malicious and selfish entities. Motivated by recent work in the application of trust and reputation to Peer-to-Peer networks, where past behaviour is used to generate trust opinions that inform future transactions, we propose an approach where the publish/subscribe infrastructure is constructed and re-configured with respect to the trust preferences of clients and routers. In this thesis, we show how Publish/Subscribe trees (PSTs) can be constructed with respect to the trust preferences of publishers and subscribers, and the overhead costs of event dissemination. Using social welfare theory, it is shown that individual trust preferences over clients and routers, which are informed by a variety of trust sources, can be aggregated to give a social preference over the set of feasible PSTs. By combining this and the existing work on PST overheads, the Maximum Trust PST with Overhead Budget problem is defined and is shown to be in NP-complete. An exhaustive search algorithm is proposed that is shown to be suitable only for very small problem sizes. To improve scalability, a faster tabu search algorithm is presented, which is shown to scale to larger problem instances and gives good approximations of the optimal solutions. The research contributions of this work are: the use of social welfare theory to provide a mechanism to establish the trustworthiness of PSTs; the finding that individual trust is not interpersonal comparable as is considered to be the case in much of the trust literature; the Maximum Trust PST with Overhead Budget problem; and algorithms to solve this problem

Inhaltlich entkoppelte Kommunikation in heterogenen, veränderlichen Netzwerktopologien

In einem von mobilen Geräten dominierten Umfeld stellt die spontane Kooperation dieser Geräte umfangreiche Anforderungen an eine geeignete Kommunikations-Middleware. Der anhaltende Trend, alle Daten zuerst in die „Cloud“ zu schicken, dort zu verarbeiten und anschließend zurück in dieselbe Umgebung zu versenden, ist in vielerlei Hinsicht unbefriedigend. Die vorliegende Dissertation schafft eine Basis zur Realisierung einer auf dem Publish-Subscribe-Paradigma aufbauenden Middleware, die inhaltlich entkoppelte Kommunikation in heterogenen, veränderlichen Umgebungen gewährleisten kann