A Robust Logical and Computational Characterisation of Peer-to-Peer Database Systems

In this paper we give a robust logical and computational characterisation of peer-to-peer (p2p) database systems. We first define a precise model-theoretic semantics of a p2p system, which allows for local inconsistency handling. We then characterise the general computational properties for the problem of answering queries to such a p2p system. Finally, we devise tight complexity bounds and distributed procedures for the problem of answering queries in few relevant special cases

04171 Abstracts Collection -- Logic Based Information Agents

From 18.04.04 to 23.04.04, the Dagstuhl Seminar 04171 ``Logic Based Information Agents\u27\u27 was held in the International Conference and Research Center (IBFI), Schloss Dagstuhl. During the seminar, several participants presented their current research, and ongoing work and open problems were discussed. Abstracts of the presentations given during the seminar as well as abstracts of seminar results and ideas are put together in this paper. The first section describes the seminar topics and goals in general. Links to extended abstracts or full papers are provided, if available

Query Answering with DBoxes is Hard

Data in description logic knowledge bases is stored in the form of an ABox. ABoxes are often confusing for developers coming from relational databases because an ABox, in contrast to a database instance, provides an incomplete specification. A recently introduced assertional component of a description logic knowledge base is a DBox, which behaves more like a database instance. In this paper, we study the data complexity of query answering in the description logic DL-Lite"F extended with DBoxes. DL-Lite"F is a description logic tailored for data intensive applications and the data complexity of query answering in DL-Lite"F with ABoxes is tractable (in AC^0). Our main result is that this problem becomes coNP-complete with DBoxes. In some expressive description logics, query answering with DBoxes also leads to a higher (combined) complexity than query answering with ABoxes. As a proof of concept, we relate query answering in ALCFIO, i.e., ALC with Functional and Inverse roles, and nOminals to the same problem in ALCFI with DBoxes. The exact complexity of the former is an open problem in the description logic literature. Here we show that query answering in ALCFIO and ALCFI with DBoxes are mutually reducible to each other in polynomial time. All the proofs in this paper are available in the appendix for the [email protected]? convenience

On the Translatability of View Updates

Abstract We revisit the view update problem and the abstract functional framework by Bancilhon and Spyratos in a setting where views and updates are exactly given by functions that are expressible in first-order logic. We give a characterisation of views and their inverses based on the notion of definability, and we introduce a general method for checking whether a view update can be uniquely translated as an update of the underlying database under the constant complement principle. We study the setting consisting of a single database relation and two views defined by projections and compare our general criterion for translatability with the known results for the case in which the constraints on the database are given by functional dependencies. We extend the setting to any number of projective views, full dependencies (that is, egd’s and full tgd’s) as database constraints, and classes of updates rather than single updates.

Effectively Updatable Conjunctive Views

The view update problem [1] consists in finding suitable ways of consistently and univocally propagating the changes introduced into a set of the view relations to the underlying database relations over which the view relations are defined. This can be formalised within a general framework [1,7] where a view is a functio