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In the recent years, a lot of attention has been paid to the development of solid foundations for the composition and inversion of schema mappings. In this paper, we review the proposals for the semantics of these crucial operators. For each of these proposals, we concentrate on the three following problems: the definition of the semantics of the operator,(More)
The inversion of schema mappings has been identified as one of the fundamental operators for the development of a general framework for metadata management. In fact, during the last years three alternative notions of inversion for schema mappings have been proposed (Fagin-inverse [10], quasi-inverse [14] and maximum recovery [2]). However, the procedures(More)
What do you do if a computational object (e.g. program trace) fails a specifica-tion? An obvious approach is to perform a repair : modify the object minimally to get something that satisfies the constraints. This approach has been investigated in the database community, for integrity constraints, and in the AI community for propositional logics. Here we(More)
What do you do if a computational object (e.g. program trace) fails a specification?An obvious approach is to perform \emph{repair}: modify the object minimally to get something that satisfies the constraints..In this paper we study repair of temporal constraints, given as automata or temporal logic formulas. We focus on determining the number of repairs(More)
A schema mapping is a specification that describes how data from a source schema is to be mapped to a target schema. Once the data has been transferred from the source to the target, a natural question is whether one can undo the process and recover the initial data, or at least part of it. In fact, it would be desirable to find a <i>reverse</i> schema(More)
In the last few years, a lot of attention has been paid to the specification and subsequent manipulation of schema mappings, a problem which is of fundamental importance in metadata management. There have been many achievements in this area, and semantics have been defined for operators on schema mappings such as composition and inverse. However, little(More)
The problems of composing and inverting schema mappings specified by source-to-target tuple-generating dependencies (st-tgds) have attracted a lot of attention, as they are of fundamental importance for the development of Bernstein's metadata management framework. In the case of the composition operator, a natural semantics has been proposed and the(More)
While monadic second-order logic is a prominent logic for specifying languages of finite words, it lacks the power to compute quantitative properties, e.g. to count. An automata model capable of computing such properties are weighted automata, but logics equivalent to these automata have only recently emerged. We propose a new framework for adding(More)
In this paper, we propose a simple and expressive framework for adding metadata to CSV documents and their noisy variants. The framework is based on annotating parts of the document that can be later used to read, query, or exchange the data. The core of our framework is a language based on extended regular expressions that are used for selecting data.(More)