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 largevolume 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.

Recent years have seen a rise in the number of unconventional

Syndication systems on the Web have attracted vast amounts of attention in recent years. As technologies have emerged and matured, there has been a transition to more expressive syndication approaches; that is, subscribers and publishers are provided with more expressive means of describing their interests and published content, enabling more accurate information filtering. In this paper, we formalize a syndication architecture that utilizes expressive Web ontologies and logic-based reasoning for selective content dissemination. This provides finer grained control for filtering and automated reasoning for discovering implicit subscription matches, both of which are not achievable in less expressive approaches. We then address one of the main limitations with such a syndication approach, namely matching newly published information with subscription requests in an efficient and practical manner. To this end, we investigate continuous query answering for a large subset of the Web Ontology Language (OWL); specifically, we formally define continuous queries for OWL knowledge bases and present a novel algorithm for continuous query answering in a large subset of this language. Lastly, an evaluation of the query approach is shown, demonstrating its effectiveness for syndication purposes. Categories and Subject Descriptors

Abstract. Most approaches to application integration require an unambiguous exchange of events. Ontologies can be used to annotate the events exchanged and thus ensure a common understanding of those events. The domain knowledge formalized in ontologies can also be employed to facilitate more intelligent, semantic event processing, but at the cost of higher processing efforts. When application integration and event processing are implemented on the user interface layer, performance is an important issue to ensure acceptable reactivity of the integrated system. In this paper, we analyze different architecture variants of implementing such an event exchange, and present an evaluation with regard to performance. An example of an integrated emergency management system is used to demonstrate those variants. 1

With the increasing popularity of wireless communication networks and mobile handheld devices, there is a pressing need to extend traditional distributed applications to mobile environments. In this paper, we propose a novel solution to support mobile clients in publish/subscribe systems. The key of our solution is the two-phase handover (2PH) protocol. In comparison with existing solutions, our solution can guarantee the exactly-once and ordered event delivery to mobile clients with very low cost, and does not require mobile clients to wait for a long time to get the undelivered events upon reconnection. Concurrent movement of multiple clients is considered and mechanisms are provided to resolve the possible conflicts during the handover processes. 1.

Abstract. We study the continuous evaluation of conjunctive triple pattern queries over RDF data stored in distributed hash tables. In a continuous query scenario network nodes subscribe with long-standing queries and receive answers whenever RDF triples satisfying their queries are published. We present two novel query processing algorithms for this scenario and analyze their properties formally. Our performance goal is to have algorithms that scale to large amounts of RDF data, distribute the storage and query processing load evenly and incur as little network traffic as possible. We discuss the various performance tradeoffs that occur through a detailed experimental evaluation of the proposed algorithms. 1

Syndication on the Web has attracted a great amount of attention in recent years. However, today’s state-of-the-art syndication approaches still provide relatively weak ex-pressive power from a modeling perspective and provide very little automated reasoning support. If a more expressive approach with a formal semantics can be provided, many benefits can be achieved, including a rich semantics-based mechanism for expressing sub-scriptions and published content and automated reasoning for discovering subscription matches not found using traditional syntactic syndication approaches. In this dissertation, I develop a syndication framework based on the Web Ontology Language (OWL), which is the standardized language for representing the semantics of information on the Web. One of the main advantages of the framework is its support for formal reasoning, as the semantics of subsets of OWL are founded in description logic (a decidable fragment of first-order logic). Therefore, the previously mentioned benefits can be achieved using description logic (DL) reasoning. However, the main limitation in using OWL as the underlying representation model is related to the overhead of DL reasoning under changing data, which makes the approach

Content-based publish/subscribe systems allow matching the content of events with predicates in the subscriptions. However, most existing systems only allow a limited set of operators, such as comparison on primitive data types (string, integer, etc). In this paper, we consider a publish/subscribe system that supports more flexible events/subscriptions with the use of advanced, yet potentially expensive, matching operators. Examples of such operators are pattern recognizers on multimedia data and spatial operators on location data. We study a critical problem in these publish/subscribe systems, namely how to optimize the matching process for a large number of subscriptions. This is achieved by exploiting the overlap in the subscriptions and sharing the operator evaluation results whenever possible. We formulate the optimal subscription evaluation problem and show that it is NP-Hard. We propose an efficient d-approximation algorithm, where d is the maximum number of operators in one subscription, as well as a heuristic algorithm that can further improve the system performance in practice. Our experiment results show that the proposed algorithms can reduce the matching cost by up to 80%, as compared to a naive strategy that evaluates the subscriptions independently.

Mobility management is an important issue for publish/subscribe systems to support mobile clients. The objectives of mobility management for publish / subscribe are to achieve short handoff delay and low message overhead, while at the same time guaranteeing reliable message delivery. Although mobility management has been extensively studied, the indirect communication style of publish/subscribe systems brings new challenges in designing mobility management solutions. In this paper, we propose a reliable and high-performance mobility management protocol, called multi-hop handoff (MHH) protocol, which sufficiently meets the requirements of publish/subscribe systems. A prototype was implemented for the MHH protocol and experiments were performed to compare the performance of MHH with two representative existing protocols. The experimental results demonstrate the efficiency improvement made by the proposed MHH protocol over the existing protocols. 1.

Interest in web-based syndication systems has been growing as information streams onto the web at an increasing rate. Technologies, like the standard Semantic Web languages RDF and OWL, make it possible to create expressive representations of the content of publications and subscriptions in a syndication framework. Because these languages are based in description logics, this representation allows the application to reasoning to make more precise matching of user interests with published information. A challenge to this approach is that the consistency of the underlying knowledge base must be maintained for these techniques to work. With the frequent addition of information from new publications, it is likely that inconsistencies will arise. There are many potential mechanisms for choosing which inconsistent information to discard from the KB to regain consistency; in the case of news syndication, we argue keeping the most trusted information is important for generating the most valuable matches. Thus, in this article, we present algorithms for belief-base revision, and specifically look at the user’s trust in the information sources as a metric for deciding what to keep in the KB and what to remove. 1