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Publications

Publications by HASLab

2002

Post-processing operators for browsing large sets of association rules

Authors
Jorge, A; Pocas, J; Azevedo, P;

Publication
DISCOVERY SCIENCE, PROCEEDINGS

Abstract
Association rule engines typically output a very large set of rules. Despite the fact that association rules are regarded as highly comprehensible and useful for data mining and decision support in fields such as marketing, retail, demographics, among others, lengthy outputs may discourage users from using the technique. In this paper we propose a post-processing methodology and tool for browsing/visualizing large sets of association rules. The method is based on a set of operators that transform sets of rules into sets of rules, allowing focusing on interesting regions of the rule space. Each set of rules can be then seen with different graphical representations. The tool is web-based and uses SVG. Association rules are given in PMML.

2001

Primary-backup replication: From a time-free protocol to a time-based implementation

Authors
Oliveira, R; Pereira, J; Schiper, A;

Publication
20TH IEEE SYMPOSIUM ON RELIABLE DISTRIBUTED SYSTEMS, PROCEEDINGS

Abstract
Fault-tolerant control systems can be built by replicating critical components. However, replication raises the issue of inconsistency. Multiple protocols for ensuring consistency have been described in the literature. PADRE (Protocol for Asymmetric Duplex Redundancy) is such a protocol, and an interesting case study of a complex and sensitive problem: the management of replicated traffic controllers in a railway system [5]. However, the low level at which the protocol lots been developed embodies system details, namely timeliness assumptions, that make it difficult to understand and may narrow its applicability. We argue that, when designing a protocol, it is preferable to consider first a general solution that does not include any timeliness assumptions; then, by taking into account additional hypothesis, one can easily design a time-based solution tailored to a specific environment. This paper illustrates the benefit of a top-down protocol design approach, and shows that PADRE can be seen as an instance of a standard Primary-backup replication protocol based on View Synchronous Communication (VSC).

2001

Probabilistic semantically reliable multicast

Authors
Pereira, J; Rodrigues, L; Oliveira, R; Kermarrec, AM;

Publication
IEEE INTERNATIONAL SYMPOSIUM ON NETWORK COMPUTING AND APPLICATIONS, PROCEEDINGS

Abstract
Traditional reliable broadcast protocols fail to scale to large settings. The paper proposes a reliable multicast protocol that integrates two approaches to deal with the large-scale dimension in group communication protocols: gossip-based probabilistic broadcast and semantic reliability. The aim of the resulting protocol is to improve the resiliency of the probabilistic protocol to network congestion by allocating scarce resources to semantically relevant messages. Although intuitively it seems that a straightforward combination of probabilistic and semantic reliable protocols is possible, we show that it offers disappointing results. Instead, we propose an architecture based on a specialized probabilistic semantically reliable layer and show that it produces the desired results. The combined primitive is thus scalable to large number of participants, highly resilient to network and process failures, and delivers a high quality data flow even when the load exceeds the available bandwidth. We present a summary of simulation results that compare different protocol configurations. © 2001 IEEE.

2001

Partial replication in the Database State Machine

Authors
Sousa, A; Pedone, F; Oliveira, R; Moura, F;

Publication
IEEE INTERNATIONAL SYMPOSIUM ON NETWORK COMPUTING AND APPLICATIONS, PROCEEDINGS

Abstract
This paper investigates the use of partial replication in the Database State Machine approach introduced earlier for fully replicated databases. It builds on the order and atomicity properties of group communication primitives to achieve strong consistency and proposes two new abstractions: Resilient Atomic Commit and Fast Atomic Broadcast. Even with atomic broadcast, partial replication requires a termination protocol such as atomic commit to ensure transaction atomicity. With Resilient Atomic Commit our termination protocol allows the commit of a transaction despite the failure of some of the participants. Preliminary, performance studies suggest that the additional cost of supporting partial replication can be mitigated through the use of Fast Atomic Broadcast.

2001

Combining interaction nets with externally defined programs

Authors
Fernández, M; Mackie, I; Pinto, JS;

Publication
APPIA-GULP-PRODE 2001: Joint Conference on Declarative Programming, Évora, Portgual, September 26-28, 2001, Proceedings, Évora, Portugal, September 26-28, 2001.

Abstract

2001

Parallel implementation models for the lambda-calculus using the geometry of interaction

Authors
Pinto, JS;

Publication
TYPED LAMBDA CALCULI AND APPLICATIONS, PROCEEDINGS

Abstract
An examination of Girard's execution formula suggests implementations of the Geometry of Interaction at the syntactic level. In this paper we limit our scope to ground-type terms and study the parallel aspects of such implementations, by introducing a family of abstract machines which can be directly implemented. These machines address all the important implementation issues such as the choice of an interthread communication model, and allow to incorporate specific strategies for dividing the computation of the execution path into smaller tasks.

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