Hojjat Jafarpour

MICS: an efficient content space representation model for publish/subscribe systems

One of the main challenges faced by content-based publish/subscribe systems is handling large amount of dynamic subscriptions and publications in a multidimensional content space. To reduce subscription forwarding load and speed up content matching, subscription covering, subsumption and merging techniques have been proposed. In this paper we propose MICS, Multidimensional Indexing for Content Space that provides an efficient representation and processing model for large number of subscriptions and publications. MICS creates a one dimensional representation for publications and subscriptions using Hilbert space filling curve. Based on this representation, we propose novel content matching and subscription management (covering, subsumption and merging) algorithms. Our experimental evaluation indicates that the proposed approach significantly speeds up subscription management operations compared to the naive linear approach.

A Fast and Robust Content-based Publish/Subscribe Architecture

We present cluster-based publish/subscribe, a novel architecture that is not only resilient to event broker failures but also provides load balancing and fast event dissemination service. Our proposed approach achieves fault tolerance by organizing event brokers in clusters. Multiple inter-cluster links provide continuous availability of dissemination service in presence of broker failure without requiring subscription retransmission or reconstruction of broker overlay. Furthermore, the proposed architecture provides a fast event dissemination infrastructure that significantly reduces subscription and publication dissemination traffic and load on event brokers. Our experimental results show that even in the presence of failures in broker network, event dissemination is not interrupted and dissemination speed and load are significantly improved compared to the existing approached.

Subscription subsumption evaluation for content-based publish/subscribe systems

In this paper we address the problem of subsumption checking for subscriptions in pub/sub systems. We develop a novel approach based on negative space representation for subsumption checking and provide efficient algorithms for subscription forwarding in a dynamic pub/sub environment. We then provide heuristics for approximate subsumption checking that greatly enhance the performance without compromising the correct execution of the system and only adding incremental cost in terms of extra computation in brokers. We illustrate the advantages of this novel approach by carrying out extensive experimentation.

CCD: efficient customized content dissemination in distributed publish/subscribe

In this paper, we propose a new content-based publish/subscribe (pub/sub) framework that enables a pub/sub system to accommodate richer content formats including multimedia publications with image and video content. The pub/sub system besides being responsible for matching and routing the published content, is also responsible for converting the content into the suitable (target) format for each subscriber. Content conversion is achieved through a set of content adaptation operators (e.g., image transcoder, document translator, etc.) at different nodes in the overlay network. We study algorithms for placement of such operators in the pub/sub broker overlay in order to minimize the communication and computation resource consumption. Our experimental results show that careful placement of these operators in pub/sub overlay network can lead to significant cost reduction.

Design and Implementation of a Middleware for Sentient Spaces

Surveillance is an important task for guaranteeing the security of individuals. Being able to intelligently monitor the activity in given spaces is essential to achieve such surveillance. Sentient spaces based on a large set of sensors provide the potential for such intelligent monitoring. However, heavily instrumenting a space with sensors it is not enough to build a sentient space. One needs a software architecture that allows programming all these sensors in a transparent and efficient manner. In this paper, we present SATware, a stream acquisition and transformation middleware we are developing to analyze, query, and transform multimodal sensor data streams to facilitate flexible development of sentient environments. SATware provides a powerful application development environment in which users (i.e., application builders) can focus on the specifics of the application without having to deal with the technical peculiarities of accessing a large number of diverse sensors via different protocols.

Tool-based configuration of real-time CORBA middleware for embedded systems

Real-time CORBA is a middleware standard that has demonstrated successes in developing distributed, realtime, and embedded (DRE) systems. Customizing real-time CORBA for an application can considerably reduce the size of the middleware and improve its performance. However, customizing middleware is an error-prone task and requires deep knowledge of the CORBA standard as well as the middleware design. This paper presents ZEN-kit, a graphical tool for customizing RTZen (an RTSJ-based implementation of real-time CORBA). This customization is achieved through modularizing the middleware so that features may be inserted or removed based on the DRE application requirements. This paper presents three main contributions: 1) it describes how real-time CORBA features can be modularized and configured in RTZen using components and aspects, 2) it provides a configuration strategy to customize real-time middleware to achieve low-footprint ORBs, and 3) it presents ZEN-kit, a graphical tool for composing customized real-time middleware.

Dynamic Load Balancing for Cluster-Based Publish/Subscribe System

In this paper we present load balancing techniques for Cluster-based pub/sub framework that include both static and dynamic load balancing. The static load balancing is done through a multi-cluster architecture for broker overlay network which is based on subscription distribution knowledge in the event space. The dynamic load balancing,on the other hand, is achieved through exploiting multiple inter-cluster and intra-cluster connections to dynamically distribute publication and subscription forwarding load among brokers during run time. Our experimental results show that the proposed load balancing techniques effectively prevent overloaded brokers without having significant effect on content dissemination efficiency.

CCD: A Distributed Publish/Subscribe Framework for Rich Content Formats

In this paper, we propose a content-based publish/subscribe (pub/sub) framework that delivers matching content to subscribers in their desired format. Such a framework enables the pub/sub system to accommodate richer content formats including multimedia publications with image and video content. In our proposed framework, users (consumers) in addition to specifying their information needs (subscription queries), also specify their profile which includes the information about their receiving context which includes characteristics of the device used to receive the content (e.g., resolution of a PDA used by a consumer). The pub/sub system besides being responsible for matching and routing the published content, also becomes responsible for converting the content into the suitable format for each user. Content conversion is achieved through a set of content adaptation operators (e.g., image transcoder, document translator, etc.). We study algorithms for placement of such operators in heterogeneous pub/sub broker overlay in order to minimize the communication and computation resource consumption. Our experimental results show that careful placement of operators in pub/sub overlay network results in significant cost reduction.

A scalable group communication mechanism for mobile agents

Many multi-agent applications based on mobile agents require message propagation among group of agents. A fast and scalable group communication mechanism can considerably improve performance of these applications. Unfortunately, most of the existing approaches do not scale well and disseminate messages slowly when the number of agents grows. In this paper, we propose Sama, a new group communication mechanism, to speed up message delivery for a group of mobile agents on a heterogeneous internetwork. The main contribution of Sama is distribution and parallelization of message propagation in an efficient way to achieve scalability and high-speed of message delivery to group members. Sama uses message dispatcher objects (MDOs), which are stationary agents on each host, to propagate messages concurrently. The proposed mechanism is independent of agent locations and transparently delivers messages to the group using constant number of remote messages. It also transparently recovers from host failures. We also present a Hop-Ring protocol that considerably improves the performance of message dissemination in Sama. Our experimental results show that message propagation in Sama is significantly fast compared to the previously proposed methods.

A Fast Group Communication Mechanism for Large Scale Distributed Objects

Group communication undoubtedly is a useful paradigm for many distributed object systems. Provision of a fast and scalable group communication mechanism can considerably improve the efficiency of these systems. In this paper, we propose a new group communication mechanism for large scale distributed objects over a huge heterogeneous inter-network. The proposed mechanism uses Message Dispatcher Objects, objects co-located with each group member to distribute and parallelize the group communication load among all group members. Our proposed mechanism also recovers from the host failure in the system. Experimental results show that our scheme scales well in a large number of group members.