Antonino Virgillito

Content-Based Publish-Subscribe over Structured Overlay Networks

This paper introduces a novel architecture for implementing content-based pub/sub communications on top of structured overlay networks. This architecture overcomes some well-known limitations of existing infrastructures, i.e. lack of self-configuration and of adaptiveness to dynamic changes. This is achieved by devising a mediator stratum between the rich event subscription semantics of content-based pub/sub systems and the standard logical addressing scheme of overlays. The paper describes details of the design and provides considerations in selecting the subscription-to-node and event-to-node mappings suitable for the solution. We identify the lack of native support for one-to-many communication by overlay networks as the main impediment for efficient system operation. The paper introduces a novel primitive for one-to-many message delivery, showing through simulation how this can improve performance of the architecture. The simulation study also shows performance comparison between the different mappings proposed as well as evaluation of other optimizations discussed in the paper

The DaQuinCIS architecture: a platform for exchanging and improving data quality in cooperative information systems

In cooperative information systems, the quality of data exchanged and provided by different data sources is extremely important. A lack of attention to data quality can imply data of low quality to spread all over the cooperative system. At the same time, improvement can be based on comparing data, correcting them and thus disseminating high quality data. In this paper, we present an architecture for managing data quality in cooperative information systems, by focusiag on two specific modules, the Data Quality Broker and the Quality Notification Service. The Data Quality Broker allows for querying and improving data quality values. The Quality Notification Service is specifically targeted to the dissemination of changes on data quality values.

Managing Data Quality in Cooperative Information Systems

Current approaches to the development of cooperative information systems are based on services to be offered by cooperating organizations, and on the opportunity of building coordinators and brokers on top of such services. The quality of data exchanged and provided by different services hampers such approaches, as data of low quality can spread all over the cooperative system. At the same time, improvement can be based on comparing data, correcting them and disseminating high quality data. In this paper, a service-based framework for managing data quality in cooperative information systems is presented. An XML-based model for data and quality data is proposed, and the design of a broker, which selects the best available data from different services, is presented. Sucha broker also supports the improvement of data based on feedbacks to source services.

Efficient Publish/Subscribe Through a Self-Organizing Broker Overlay and its Application to SIENA

Recently many scalable and efficient solutions for event dissemination in publish/subscribe (pub/sub) systems have appeared in the literature. This dissemination is usually done over an overlay network of brokers and its cost can be measured as the number of messages sent over the overlay to allow the event to reach all intended subscribers. Efficient solutions to this problem are often obtained through smart dissemination algorithms that avoid flooding events on the overlay. In this paper, we propose a complementary approach that obtains efficient event dissemination by reorganizing the overlay network topology. More specifically, this reorganization is done through a self-organizing algorithm executed by brokers whose aim is to directly connect, through overlay links, pairs of brokers matching same events. In this way, on average, the number of brokers involved in an event dissemination decreases, thus reducing its cost. Even though the paradigm of the self-organizing algorithm is general and then applicable to any overlay-based pub/sub system, its concrete implementation depends on the specific system. As a consequence, we studied the effect of the introduction of the self-organizing algorithm in the context of a specific system implementing a tree-based routing strategy, namely SIENA, showing the actual performance benefits through an extensive simulation study. In particular, performance results point out the capacity of the algorithm to converge to an overlay topology accommodating efficient event with respect to (w.r.t) dissemination a specific scenario. Moreover, the algorithm shows a significant capacity to adapt the overlay network topology to continuously changing scenarios while keeping an efficient behavior w.r.t. event dissemination.

A Semantic Overlay for Self- Peer-to-Peer Publish/Subscribe

Publish/Subscribe systems provide a useful platform for delivering data (events) from publishers to subscribers in an anonymous fashion in distributed networks. In this paper, we promote a novel design principle for self-. dynamic and reliable content-based publish/subscribe systems and perform a comparative analysis of its probabilistic and deterministic implementations. More specifically, we present a generic content-based publish/subscribe system, called DPS (Dynamic Publish/Subscribe). DPS combines classical content-based filtering with self-. (self-organizing, selfconfiguring, and self-healing) subscription-driven clustering of subscribers. DPS gracefully adapts to failures and changes in the system while achieving scalable events delivery. DPS includes a variety of fault-tolerant deterministic and probabilistic content-based publication/subscription schemes. These schemes are targeted toward scalability, and aim at reducing and distributing the number of messages exchanged. Reliability and scalability of our system are shown through analytical and experimental evaluation.

A distributed mutual exclusion algorithm for mobile ad-hoc networks

A distributed mutual exclusion algorithm based on token exchange and well suited for mobile ad-hoc networks is presented along with a simulation study. The algorithm is based on a dynamic logical ring and combines the best from two families of token based algorithms (i.e., token-asking and circulating token). In this way, the number of messages exchanged per critical section (CS) access (the main performance index for such algorithms) tends to optimal values under a heavy request load (i.e., two application messages for each CS access). We present a simulation study that (i) confirms this optimality and (ii) shows that, in a mobile ad-hoc network, an effective reduction in the number of hops per application message can be achieved by using a specific policy to build the logical ring on-the-fly.

The evolution of publish/subscribe communication systems

In the last years, a growing attention has been paid to the publish/subscribe (pub/sub) communication paradigm as a mean for disseminating information (also called events) through distributed systems on wide-area networks. Participants to the communication can act as publishers, that submit information to the system, and as subscribers, that express their interest in specific types of information. Main characteristics of such manyto- many communication paradigm are: the interacting parties do not need to know each other (anonymity), partners do not need to be up at the same time (decoupling in time), and the sending/receipt does not block participants (decoupling in flow). So, the publish/ subscribe paradigm has been largely recognized as the most promising applicationlevel communication paradigm for integration of information systems.

Modeling publish/subscribe communication systems: towards a formal approach

Publish/subscribe is a widespread communication paradigm for asynchronous messaging that naturally fits the decoupled nature of distributed systems, allowing simple and effective development of distributed applications. In this paper we propose a framework, which includes a model of a publish/subscribe computation and a few properties on the computation, namely completeness and minimality, which capture, from an application viewpoint, the expected behavior of a publish/subscribe system with respect to the semantic of the notification of the information. Finally, we provide also a centralized implementation of publish/subscribe system which produces minimal and complete computations.

On the modelling of publish/subscribe communication systems

This paper presents a formal framework of a distributed computation based on a publish/subscribe system. The framework abstracts the system through two delays, namely the subscription/unsubscription delay and the diffusion delay. This abstraction allows one to model concurrent execution of publication and subscription operations without waiting for the stability of the system state and to define a Liveness property which gives the conditions for the presence of a notification event in the global history of the system. This formal framework allows us to analytically define a measure of the effectiveness of a publish/subscribe system, which reflects the percentage of notifications guaranteed by the system to subscribers. A simulation study confirms the validity of the analytical measurements. Copyright

Distributed Event Routing in Publish/Subscribe Systems

Since the early nineties, anonymous and asynchronous dissemination of information has been a basic building block for typical distributed applications such as stock exchanges, news tickers and air-traffic control. With the advent of ubiquitous computing and of the ambient intelligence, information dissemination solutions have to face challenges such as the exchange of huge amounts of information, large and dynamic number of participants possibly deployed over a large network (e.g. peer-to-peer systems), mobility and scarcity of resources (e.g. mobile ad hoc and sensor networks) [53].