The JEDI event-based infrastructure and its application to the development of the OPSS WFMS

Abstract

The development of complex distributed systems demands for the creation of suitable architectural styles (or paradigms) and related run-time infrastructures. An emerging style that is receiving increasing attention is based on the notion of event. In an event-based architecture, distributed software components interact by generating and consuming events. An event is the occurrence of some state change in a component of a software system, made visible to the external world. The occurrence of an event in a component is asynchronously notified to any other component that has declared some interest in it. This paradigm (usually called "publish/subscribe" from the names of the two basic operations that regulate the communication) holds the promise of supporting a flexible and effective interaction among highly reconfigurable, distributed software components.In the past two years, we have developed an object-oriented infrastructure called JEDI (Java Event-based Distributed Infrastructure). JEDI supports the development and operation of event-based systems and has been used to implement a significant example of distributed system, namely, the OPSS workflow management system (WFMS). The paper illustrates JEDI main features and how we have used them to implement OPSS. Moreover, the paper provides an initial evaluation of our experiences in using the event-based architectural style and a classification of some of the event-based infrastructures presented in the literature. KeywordsEvent-based systems, distributed systems, software architectures, workflow, business processes, object-orientation, publish/subscribe middleware.Convergence between telecommunication, broadcasting, and computing is opening new opportunities and challenges for a potentially large market of innovative network-wide services. The class of users interested by this revolution is significantly large: families, professionals, large organizations, government agencies, and administrations. The services range from home banking and electronic commerce, to coordination and workflow support for large dispersed teams, within the same company or even across multiple companies. Many research and industrial activities are currently being carried out to identify feasible strategies to develop and operate these services in an effective and economically viable way. The requirements and technical problems that have to be addressed are complex and critical:• Services must be able to operate on a wide area network with acceptable performance.• The software technology used to implement these services must be "light", i.e., it should be scalable in terms of the number of both components and users involved and of their distribution.• The technology must enable a "plug and play" approach to support dynamic reconfiguration and introduction of new service components.• Finally, it is essential to support openness and interoperability between different platforms since the services are usually implemented in a heterogeneous hardware infrastructure.To foster the diffusion of netw...

Adaptive Content-Based Routing in General Overlay Topologies

“…Typically, content-based pub/sub systems are built as application-level overlays of content-based pub/sub brokers, with publishing data sources and subscribing data sinks connecting to the broker overlay as clients. In pub/sub systems, event filtering is supported by atomic subscriptions, whereas composite subscriptions are used by more sophisticated pub/sub applications to correlate events from distributed sources [5,7,14,29]. To support the class of applications above, this paper considers both atomic and composite subscriptions.…”

“…Publish/subscribe (pub/sub) is a powerful messaging paradigm that maintains a clean decoupling of data sources and sinks [3,4,5,8,14,24,31,34]. Interoperating through simple publish and subscribe invocations is especially useful for the development of large, distributed, loosely coupled systems.…”

“…While there are many applications based on group communication and topic-based pub/sub protocols such as information dissemination [17,22], a large variety of emerging applications benefit from the expressiveness, filtering, distributed event correlation, and complex event processing capabilities of content-based pub/sub. These applications include RSS feed filtering [31], stock-market monitoring engines [33], system and network management and monitoring [7,20], algorithmic trading with complex event processing [10,29], business process execution [32], business activity monitoring [7] and workflow management [5]. Typically, content-based pub/sub systems are built as application-level overlays of content-based pub/sub brokers, with publishing data sources and subscribing data sinks connecting to the broker overlay as clients.…”

MEDYM: Match-Early with Dynamic Multicast for Content-Based Publish-Subscribe Networks

“…However, different from IP addresses, content-based subscriptions from servers geographically close are not necessarily similar and may not be succinctly summarized. Therefore, a similar hierarchy structure for pub-sub network can impose heavy load on servers at the upper level of the hierarchy [6] [9]. Based on our experience from an earlier work [4], we propose a different hierarchical solution called for MEDYM, called H-MEDYM for Hierarchical MEDYM.…”

“…Many other distributed pub-sub systems follow the CBF approach. In JEDI [9], a hierarchical event routing network was proposed, but was found to perform worse than the peer-to-peer topology in [6]. The Gryphon group [1][26] designed efficient content-based matching algorithms used in forwarding, and proposed using virtual time vectors to convey temporal consistency of subscription propagation.…”