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Data Integration in Peer-to-Peer (P2P) systems is concerned with the ability of physically connect autonomous sources (peer) for sharing and reuse information and for the creation of new information from existing one. In a P2P system a query can be posed to any peer and the answer is provided by integrating locally stored data with data provided from its neighbors. Anyhow, while collecting data for answering queries, imported data may corrupt the local database due to the violation of some integrity constraint, therefore inconsistencies have to be managed. This paper contributes to the proposal of a logic based framework for data integration and query answering in a Peer-to-Peer environment. It is based on [11,12] in which the Preferred Weak Model Semantics, capturing a different perspective for P2P data integration, has been proposed: just data not violating integrity constraints are exchanged among peers by using mapping rules. The motivation of this work stems from the observation that the complexity of computing preferred weak models in [11,12] does not let the approach to be implemented in practical applications. Therefore, a more pragmatic solution seems to be desirable for assigning semantics to a P2P system. First, the paper proposes a rewriting technique that allows modeling a P2P system, ${\mathcal {PS}}$, as a unique logic program, Rewt(${\mathcal {PS}}$), whose stable models correspond to the preferred weak models of ${\mathcal {PS}}$. Then, it presents the Well Founded Model Semantics, that allows obtaining a deterministic model whose computation is polynomial time. This is a (partial) stable model obtained by evaluating with a three-value semantics a logic program obtained from Rewt(${\mathcal {PS}})$. Finally, the paper provides results on the complexity of answering queries in a P2P system. [ABSTRACT FROM AUTHOR]

The aim of this paper consists in investigating the problem of managing inconsistent databases, i.e. databases violating integrity constraints. A flurry of research on this topic has shown that the presence of inconsistent data can be resolved by "repairing" the database, i.e. by providing a computational mechanism that ensures obtaining consistent "scenarios" of the information or by consistently answer to queries posed on an inconsistent set of data. This paper considers preferences among repairs and possible answers by introducing a partial order among them on the basis of some preference criteria. Moreover, the paper also extends the notion of preferred consistent answer by extracting from a set of preferred repaired database, the maximal consistent overlapping portion of the information, i.e. the information supported by each preferred repaired database. [ABSTRACT FROM AUTHOR]

The increasing availability of portable computing devices has enabled wireless networking to support mobile users in experiencing emerging applications and services. In this paper we extend a previously proposed work on supporting users for personalized navigation of websites, to make it mobile-aware. The objective is to provide personalization, in form of page recommendations, w.r.t. a specific context of use. In particular, we exploit information on user physical location in detecting navigational preferences, and device/network information to address application adaptability. [ABSTRACT FROM AUTHOR]

The present work proposes a new semantics for logic program with preference rules and studies logic programs enriched with both aggregates and preference rules. The interest of research literature in handling user preferences to express a partial order on rules and literals is reflected by an extensive number of proposals. The association of aggregates and preferences is, here, used to also express a partial order on global models, other than on literals and rules, so that optimization problems can be expressed in a simple and elegant way. The use of aggregates makes logic languages more flexible and intuitive, without any additional computational complexity. [ABSTRACT FROM AUTHOR]

The problem of repairing XML data which are inconsistent and incomplete with respect to a set of integrity constraints and a DTD is addressed. The existence of repairs (i.e. minimal sets of update operations making data consistent) is investigated and shown to be undecidable in the general case. This pro-blem is shown to be still undecidable when data are interpreted as "incomplete" (so that they could be repaired by performing insert operations only). However, it becomes decidable when particular classes of constraints are considered. The existence of repairs is proved to be decidable and, in particular, $\cal NP$-complete, if inconsistent data are interpreted as "dirty" data (so that repairs are data-cleaning operations consisting in only deletions). The existence of general repairs (containing both insert and delete operations) for special classes of integrity constraints (functional dependencies) is also investigated. Finally, for all the cases where the existence of a repair is decidable, the complexity of providing consistent answers to a query (issued on inconsistent data) is characterized. [ABSTRACT FROM AUTHOR]