José Legatheaux Martins

Routing algorithms for content-based publish/subscribe systems

In content-based publish/subscribe systems, messages target a dynamic group of participants whose expressed interests match the contents of the messages. In this generalization of multicasting communication, also dubbed content-based networking, naming, binding and communication are intertwined in the same substrate. Optimal content-based routing uses dissemination trees dynamically pruned to only cover the matching subscribers. It is a complex problem that has motivated significant research efforts. This paper presents a compilation of the main algorithms for routing messages in distributed content-based publish-subscribe systems proposed and published in the last decade. Discussion is focused on the content-based routing problem in respect to optimality, complexity and applicability. Moreover, whenever it is appropriate, the algorithms covered are also matched to similar algorithms familiar to the networking community, setting this paper apart from other surveys on the broad topic of publish/subscribe systems.

Mobile Transaction Management in Mobisnap

In this paper we describe a transaction management system designed to face the inherent characteristics of mobile environments. Mobile clients cache subsets of the database state and allow disconnected users to perform transactions independently. Transactions are specified as mobile transactional programs that are propagated and executed in the server, thus allowing the validation of transactions based on application-specific semantics. In the proposed model (as in others previously presented in literature) the final result of a transaction is only determined when the transaction is processed in the central server. Users may be notified of the results of their transactions using system support (even when they are no longer using the same application or even the same computer). Additionally, the system implements a reservation mechanism in order to guarantee the results of transactions performed in disconnected computers.

Revisiting hierarchical quorum systems

In distributed systems, it is often necessary to provide coordination among the multiple concurrent processes. Quorum systems provide a decentralized approach to provide such coordination that is resilient to node and communication link failures. Quorum systems are highly available and may be used to balance the load among the elements of the system. In this paper, we propose a modification to the hierarchical grid quorum system that leads to a smaller quorum size and better availability and load. We also propose a new hierarchical quorum construction based on the organization of elements in a triangular shape that presents better average quorum size, availability and load than other highly-available systems with almost optimal load.

A flexible object-group-oriented framework to support large scale collaborative applications

Recent results of distributed systems research in multicasting and group oriented communication systems and protocols, are very attractive to implement multiparticipant and collaborative applications. We examine the requirements and criteria placed by large scale cooperative applications, namely those alternating multiparticipant synchronous work sessions with asynchronous interactions and disconnected work. We propose a topology organization, an architectural model and the materialization of an integrated generic platform to support those requirements. We argue about the necessary evolution from the well known client/server model to new paradigms involving collaborative-object-group orientation. We describe the implementation of an object-group-oriented infrastructure as well as a generic programming framework offering high flexibility.

Coordination support for scalable collaborative work

In this paper we discuss the principles, design options and implementation issues to support coordination and awareness services in the context of scalable CSCW sessions. We analyze essential differences between the coordination support needed by these sessions when compared with the conventional coordination activity within workflow systems. Then we propose a flexible support model, which is more adequate for group-oriented collaborative work tasks developed in the context of a more complex workgroup activity. The support is concerned with a set of adaptable mechanisms as well as system base components and services provided by an integrated, open and extensible support platform. These components implement a set of facilities for coordination and awareness control in the context of collaboration sessions.