Practical high-throughput content-based routing using unicast state and probabilistic encodings

We address the problem that existing publish/subscribe messaging systems, including such commonly used ones as Apache’s ActiveMQ and IBM’s WebSphere MQ, exhibit degraded end-to-end throughput performance in a wide-area network setting. We contend that the cause of this problem is the lack of an appropriate routing protocol. Building on the idea of a content-based network, we introduce a protocol called B-DRP that can demonstrably improve the situation. A content-based network is a content-based publish/subscribe system architected as a datagram network: a message is forwarded hop-by-hop and delivered to any and all hosts that have expressed interest in the message content. This fits well with the character of a wide-area messaging system. B-DRP is based on two main techniques: a message delivery mechanism that utilizes and exploits unicast forwarding state, which can be easily maintained using standard protocols, and a probabilistic data structure to effciently represent and evaluate receiver interests. We present the design of B-DRP and the results of an experimental evaluation that demonstrates its support for improved throughput in a wide-area setting

An Integrated Alerting Service for Open Digital Libraries: Design and Implementation

Alerting services can provide a valuable support for information seeking in Digital Libraries (DL). Several systems have been proposed. Most of them have serious drawbacks, such as limited expressiveness, limited coverage, and poor support of federated and distributed collections. In this paper, we present the detailed design and implementation for a comprehensive alerting service for digital libraries. We demonstrate typical user interactions with the system. Our alerting service is open to other event sources, supports a rich variety of event types, and works on distributed as well as on federated DL collections

Efficient Content-based Routing, Mobility-aware Topologies, and Temporal Subspace Matching

Event-based systems are seen as good candidates for supporting distributed applications in dynamic and ubiquitous environments because they support decoupled and asynchronous many-to-many information dissemination. Event systems are widely used, because asynchronous messaging provides a flexible alternative to RPC (Remote Procedure Call). They are typically implemented using an overlay network of routers. A content-based router forwards event messages based on filters that are installed by subscribers and other routers. The filters are organized into a routing table in order to forward incoming events to proper subscribers and neighbouring routers. This thesis addresses the optimization of content-based routing tables organized using the covering relation and presents novel data structures and configurations for improving local and distributed operation. Data structures are needed for organizing filters into a routing table that supports efficient matching and runtime operation. We present novel results on dynamic filter merging and the integration of filter merging with content-based routing tables. In addition, the thesis examines the cost of client mobility using different protocols and routing topologies. We also present a new matching technique called temporal subspace matching. The technique combines two new features. The first feature, temporal operation, supports notifications, or content profiles, that persist in time. The second feature, subspace matching, allows more expressive semantics, because notifications may contain intervals and be defined as subspaces of the content space. We also present an application of temporal subspace matching pertaining to metadata-based continuous collection and object tracking.Tapahtumapohjaiset järjestelmät nähdään hyvänä tapana tukea ja kehittää hajautettuja sovelluksia dynaamisissa ympäristöissä. Nämä järjestelmät tukevat asynkronista viestien välitystä. Tapahtumapohjaisia järjestelmiä käytetään, koska asynkroninen viestintä mahdollistaa etäproseduurikutsuja vapaammat sidokset sovellusten välille. Tapahtumapohjaiset järjestelmät toteutetaan tyypillisesti ns. "overlay" verkkoina sovelluskerroksella. Sisältöpohjainen reititin välittää tapahtumaviestejä tilaajien asettamien suotimien (eng. filter) perusteella. Tiedon tilaajat ja tuottajat kytketään suotimien avulla niin että tuottajien tuottamat tapahtumat välittyvät aktiivisille tilaajille. Suodin valikoi viestivirrasta halutut viestit erityisten sääntöjen avulla. Suotimet järjestetään reititystauluksi, jonka perusteella päätetään kenelle reititin ohjaa viestejä. Väitöskirja käsittelee suodinpohjaisten reititystaulujen optimointia ja esittää uusia tietorakenteita ja konfiguraatioita paikalliseen sekä hajautettuun toimintaan. Työssä esitetään yleinen formaali suotimien yhdistämismalli, joka integroidaan esitettyjen tietorakenteiden kanssa. Lisäksi työssä tutkitaan liikkuvien tilaajien ja tuottajien aiheuttamia kustannuksia. Työssä esitetään myös uusi tekniikka aikaan kytketyn tiedon välitykseen. Tekniikka yhdistää kaksi uutta piirrettä. Ensimmäinen piirre on temporaalinen toiminta, jossa välitettävä tieto on määritetty olemaan voimassa tietyn ajanjakson. Toinen ominaisuus mahdollistaa sekä kyselyiden että datan, johon kyselyt kohdistuvat, määrittelyn moniulotteisten suotimien avulla. Työssä esitetään tekniikasta esimerkkisovellus, joka käsittelee joukkojen ja olioiden seurantaa

Confidentiality-Preserving Publish/Subscribe: A Survey

Publish/subscribe (pub/sub) is an attractive communication paradigm for large-scale distributed applications running across multiple administrative domains. Pub/sub allows event-based information dissemination based on constraints on the nature of the data rather than on pre-established communication channels. It is a natural fit for deployment in untrusted environments such as public clouds linking applications across multiple sites. However, pub/sub in untrusted environments lead to major confidentiality concerns stemming from the content-centric nature of the communications. This survey classifies and analyzes different approaches to confidentiality preservation for pub/sub, from applications of trust and access control models to novel encryption techniques. It provides an overview of the current challenges posed by confidentiality concerns and points to future research directions in this promising field

Evaluating Tree Pattern Similarity for Content-based Routing Systems

With the advent of XML as the de facto language for data interchange, scalable distribution of data to large populations of consumers remains an important challenge. Content-based publish/subscribe systems offer a convenient abstraction for data producer and consumers, as most of the complexity related to addressing and routing is encapsulated within the network infrastructure. Data consumers typically specify their subscriptions using some XML pattern specification language (e.g., XPath), while producers publish content without prior knowledge of the recipients, if any. A novel approach to content-based routing consists in organizing consumers with similar interests in peer-to-peer semantic communities inside which XML documents are propagated. In order to build semantic communities and connect peers that share common interests with each other, one needs to evaluate the similarity between their subscriptions. In this paper, we specifically address this problem and we propose novel algorithms to compute the similarity of seemingly unrelated tree patterns by taking advantage of information derived from the XML document types, such as valid combinations of elements, or conjunctions and disjunctions on their occurrence. These results are of interest in their own right, and can prove useful in other domains, such as approximate XML queries involving tree patterns. Results from a prototype implementation validate the effectiveness of our approach

Scaling SDI systems via query clustering and aggregation

Master'sMASTER OF SCIENC