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The problem of rewriting a query using a materialized view is studied for a well known fragment of XPath that includes the following three constructs: wildcards, descendant edges and branches. In earlier work, determining the existence of a rewriting was shown to be coNP-hard, but no tight complexity bound was given. While it was argued that(More)
An unfold/fold program transformation system which extends the unfold/fold transformations of H. Tamaki and T. Sato is presented in this paper. The system consists of unfolding, simultaneous folding , and generalization + equality introduction rules. The simultaneous folding rule permits the folding of a set of folded clauses into a single clause, using a(More)
We consider the problem of extending temporal deductive databases with stratified negation. We argue that the classical stratification test for deductive databases is too restrictive when one shifts attention to the temporal case. Moreover, as we demonstrate, the (more general) local stratification approach is impractical: detecting whether a temporal(More)
In this paper, we address a problem common in the frame of WWW, namely, representing information that assumes different facets under different contexts (sets of worlds). For expressing context-dependent (or multidimensional) data, we introduce Multidimensional Semi-structured Data, where context is defined through (dimension, value) pairs. An extension of(More)
We consider the problem of answering datalog queries using materialized views. More speciically, queries are rewritten to refer to views instead of the base relations over which the queries were originally written. Much work has been done on program rewriting that produces an equivalent query. In the context of information integration, though, the(More)
Metadata interoperability is an active research area, especially for cultural heritage collections, which consist of heterogeneous objects described by a variety of metadata schemas. In this paper we propose an ontology-based metadata interoperability approach, which exploits, in an optimal way, the semantics of metadata schemas. In particular, we propose(More)
In this paper, we propose an ontology-based metadata integration methodology for the cultural heritage domain. The proposed real-world approach considers an integration architecture in which CIDOC/CRM ontology acts as a mediating scheme. In this context, we present a mapping methodology from Encoded Archival Description (EAD) and Dublin Core (DC) metadata(More)
In this paper we address an issue common in the frame of WWW, namely information entities that present diierent facets under diierent contexts (or worlds). Handling such m ultifacet or multidimen-sional entities requires a multidimensional paradigm for Web data, which consists of representation, manipulation and presentation issues. For representing(More)
Temporal programming languages provide a powerful means for the description and implementation of dynamic systems. However, most temporal languages are based on linear time, a fact that renders them unsuitable for certain types of applications (such as expressing properties of nondeterministic programs). In this paper we introduce the new temporal logic(More)