Abstract

Abstract
Network clustering problem (NCP) is the problem associated to the detection of network community structures. Building on Markov random walks we address this problem with a new ant colony optimization strategy, named as ACOMRW, which improves prior results on the NCP problem and does not require knowledge of the number of communities present on a given network. The framework of ant colony optimization is taken as the basic framework in the ACOMRW algorithm. At each iteration, a Markov random walk model is taken as heuristic rule; all of the ants' local solutions are aggregated to a global one through clustering ensemble, which then will be used to update a pheromone matrix. The strategy relies on the progressive strengthening of within-community links and the weakening of between-community links. Gradually this converges to a solution where the underlying community structure of the complex network will become clearly visible. The performance of algorithm ACOMRW was tested on a set of benchmark computer-generated networks, and as well on real-world network data sets. Experimental results confirm the validity and improvements met by this approach.

Abstract

Abstract

Abstract
Version vectors (VV) are used pervasively to track dependencies between replica versions in multi-version distributed storage systems. In these systems, VV tend to have a dual functionality: identify a version and encode causal dependencies. In this paper, we show that by maintaining the identifier of the version separate from the causal past, it is possible to verify causality in constant time (instead of O(n) for VV) and to precisely track causality with information with size bounded by the degree of replication, and not by the number of concurrent writers. © 2012 Authors.

Abstract
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. © Springer-Verlag Berlin Heidelberg 2000.