Manolis Gergatsoulis

Learn More
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)
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)
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)
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)
Multidimensional semistructured data (MSSD) are semistructured data that present different facets under different contexts. Context represents alternative worlds, and is expressed by assigning values to a set of user-defined variables called dimensions. The notion of context has been incorporated in the Object Exchange Model (OEM), and the extended model is(More)
In this paper we investigate various aspects of representing multidimensional information in the frame of the WWW. Multidimen-sional XML (MXML) is an extension of XML suitable for representing data that assume different facets, having different value or different structure, under different contexts. In Multidimensional XML, elements and attributes may(More)