Milenko Petrovic

S-ToPSS: semantic Toronto publish/subscribe system

Publisher Summary This chapter discusses the semantic Toronto publish/subscribe system. Middleware that can satisfy this requirement include event-based architectures such as publish-subscribe systems. The pub/sub paradigm has recently gained a significant interest in the database community for the support of information dissemination applications for which other models turned out to be inadequate. In pub/sub systems, clients are autonomous components that exchange information by publishing events and by subscribing to the classes of events, they are interested in. In these systems, publishers produce information, while subscribers consume it. A component usually generates a message when it wants the external world to know that a certain event has occurred. All components that have previously expressed their interest in receiving such events will be notified about it. The central component of this architecture is the event dispatcher. This component records all subscriptions in the system. When a certain event is published, the event dispatcher matches it against all subscriptions in the system.

G-ToPSS: fast filtering of graph-based metadata

RDF is increasingly being used to represent metadata. RDF Site Summary (RSS) is an application of RDF on the Web that has considerably grown in popularity. However, the way RSS systems operate today does not scale well. In this paper we introduce G-ToPSS, a scalable publish/subscribe system for selective information dissemination. G-ToPSS is particularly well suited for applications that deal with large-volume content distribution from diverse sources. RSS is an instance of the content distribution problem. G-ToPSS allows use of ontology as a way to provide additional information about the data. Furthermore, in this paper we show how G-ToPSS can support RDFS class taxonomies. We have implemented and experimentally evaluated G-ToPSS and we provide results in the paper demonstrating its scalability compared to alternatives.

Content-based routing in mobile ad hoc networks

The publish/subscribe model of communication provides sender/receiver decoupling and selective information dissemination that is appropriate for mobile environments characterized by scarce resources and a lack of fixed infrastructure. We propose and evaluate three content-based routing protocols: CBR is an adaptation of existing distributed publish/subscribe protocols for wired networks, FT-CBR extends CBR to provide fault-tolerance, and RAFT-CBR provides both fault-tolerance and reliability. Using network simulations we analyze the applicability and test the tradeoffs of these algorithms. We show that RAFT-CBR can guarantee 100% delivery to small groups, at the expense of transmission delay. CBR, with a low message overhead and low delay, is more suitable for larger groups at the expense of reliability. FT-CBR provides comparable delivery rates to RAFT-CBR, as well as low delay, at the expense of increased message cost.

Effects of routing computations in content-based routing networks with mobile data sources

This paper presents the first quantitative evaluation of the role of routing computations on performance when mobility is introduced to a content-based routing network. Additionally, the paper identifies the factors that affect the performance of a distributed publish/subscribe architecture supporting mobile publishers, formalizes publisher mobility protocols for distributed publish/subscribe systems, and develops and evaluates protocols that reduce the costs associated with supporting mobile publishers in publish/subscribe systems. Our results show that ignoring route computation time paints a false picture of the scalability of content-based routing networks, but that with appropriate protocols the adverse effects can be mitigated.

Publisher mobility in distributed publish/subscribe systems

The decoupling of producers and consumers in the publish/subscribe paradigm lends itself well to the support of mobile users who roam about the environment with intermittent network connectivity. This paper presents the first quantitative evaluation of publisher mobility in a distributed publish/subscribe system. Our results indicate that publisher mobility breaks a fundamental assumption of publish/subscribe systems and has a significant performance impact. We formalize publisher mobility algorithms for a distributed publish/subscribe system, and develop and evaluate optimizations to the mobile publisher algorithms.

Performance of TCP/UDP under ad hoc IEEE802.11

TCP is the de facto standard for connection oriented transport layer protocol, while UDP is the de facto standard for transport layer protocol, which is used with real time traffic for audio and video. Although there have been many attempts to measure and analyze the performance of the TCP protocol in wireless networks, very few research was done on the UDP or the interaction between TCP and UDP traffic over the wireless link. We study the performance of TCP and UDP over IEEE802.11 ad hoc network. We used two topologies, a string and a mesh topology. Our work indicates that IEEE802.11 as a ad-hoc network is not very suitable for bulk transfer using TCP. It also indicates that it is much better for real-time audio. Although one has to be careful here since real-time audio does require much less bandwidth than the wireless link bandwidth. Careful and detailed studies are needed to further clarify that issue.

Optimized cluster-based filtering algorithm for graph metadata

With the increasing amount of information on the Web and the proliferation of RSS offerings, efficient graph-based metadata filtering algorithm for large scale information dissemination is very important today. Matching graph-based documents is expensive due to the expressiveness of the language. The centralized architecture does not work well for the large scale information dissemination service. To address these problems, in this paper we develop a cluster-based publish/subscribe system for filtering graph-based RSS documents. Essentially, we develop two indexing algorithms to enable workload distribution and cluster-based filtering. Furthermore, we proposed an optimized graph matching algorithm which speeds up the constraint evaluation for subscriptions. The experimental results show that we can support one million subscriptions on a compute cluster with 5-20 nodes and the throughput scales linearly with the number of cluster nodes.

Impact of atmospheric correction and image filtering on hyperspectral classification of tree species using support vector machine

Abstract. Hyperspectral images can be used to identify savannah tree species at the landscape scale, which is a key step in measuring biomass and carbon, and tracking changes in species distributions, including invasive species, in these ecosystems. Before automated species mapping can be performed, image processing and atmospheric correction is often performed, which can potentially affect the performance of classification algorithms. We determine how three processing and correction techniques (atmospheric correction, Gaussian filters, and shade/green vegetation filters) affect the prediction accuracy of classification of tree species at pixel level from airborne visible/infrared imaging spectrometer imagery of longleaf pine savanna in Central Florida, United States. Species classification using fast line-of-sight atmospheric analysis of spectral hypercubes (FLAASH) atmospheric correction outperformed ATCOR in the majority of cases. Green vegetation (normalized difference vegetation index) and shade (near-infrared) filters did not increase classification accuracy when applied to large and continuous patches of specific species. Finally, applying a Gaussian filter reduces interband noise and increases species classification accuracy. Using the optimal preprocessing steps, our classification accuracy of six species classes is about 75%.

The European Union and its post-communist neighbours: EU enlargement and the European Neighbourhood Policy

Relations with the countries of former communist Eastern Europe have been a very important aspect of the European Union’s (EU) external relations and, according to many, are one of the most successful products of its common foreign policy over the last two decades, especially regarding the outcomes of the policy and process of the EU’s eastern enlargement. However, the EU’s policy towards and established relations with the countries of the former communist bloc have not been uniform and are not the result of a carefully prepared, well-designed and long-term strategy. In many aspects, they are direct and to some extent spontaneous outcomes of developments that followed the sudden collapse of the communist bloc in Eastern Europe and the transformation of the European Community into the more integrated European Union, with its expected “common foreign policy” (European Council, 1991) in the western part of the European continent.

In Croatia’s slipstream or on an alternative road? Assessing the objective case for the remaining Western Balkan states acceding into the EU

Since the ‘mega-enlargement’ of the European Union into the erstwhile communist territories of Eastern Central Europe and the Baltics in 2004/2007, the prospect for further EU enlargement(s) has seriously dissipated. Terms such as ‘enlargement fatigue’ and ‘absorption capacity’ have become en vogue in the post-2007 enlargement setting where older EU member states have developed negative attitudes towards future enlargements. However, the accession of Croatia into the EU in 2013 has inevitably raised questions of which states or regions could be next. This paper contends that due to a multitude of issues surrounding Turkey, particularly the political impasse within the EU towards Turkish accession coupled with its sheer size, only the smaller states of the Western Balkans represent viable candidates (Iceland’s accession prospects have stalled significantly due to internal pressures). This paper argues that the limits of EU eastern enlargement are set by both prevailing (subjectively defined) political attitudes founded on various grounds in the leading EU member states and by the rationally defined objective capacity of the EU’s institutions to absorb potential new member states. It is through the latter, and in comparison to the three most recent accession states - Bulgaria, Romania and Croatia – which this paper attempts to assess the objective potential of the remaining Western Balkan states to accede into the EU in the near future.