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Motivated by reasoning tasks for XML languages, the satisfiability problem of logics on <i>data trees</i> is investigated. The nodes of a data tree have a <i>label</i> from a finite set and a <i>data value</i> from a possibly infinite set. It is shown that satisfiability for two-variable first-order logic is decidable if the tree structure can be accessed(More)
In a data word each position carries a label from a finite alphabet and a data value from some infinite domain. These models have been already considered in the realm of semistructured data, timed automata and extended temporal logics. It is shown that satisfiability for the two-variable first-order logic FO<sup>2</sup>(~,&lt;,+1) is decidable over finite(More)
We investigate the question of whether a query <i>Q</i> can be answered using a set V of views. We first define the problem in information-theoretic terms: we say that V determines <i>Q</i> if V provides enough information to uniquely determine the answer to <i>Q.</i> Next, we look at the problem of rewriting <i>Q</i> in terms of V using a specific(More)
This paper investigates the on-line validation of streaming XML documents with respect to a DTD, under memory constraints. We first consider validation using constant memory, formalized by a finite-state automaton (<sc>FSA</sc>). We examine two flavors of the problem, depending on whether or not the XML document is assumed to be well-formed. The main(More)
In a <i>data word</i> each position carries a label from a finite alphabet and a data value from some infinite domain. This model has been already considered in the realm of semistructured data, timed automata, and extended temporal logics. This article shows that satisfiability for the two-variable fragment FO<sup>2</sup>(&sim;,&lt;,+1) of first-order(More)
This paper presents DEDALE, a spatial database system intended to overcome some limitations of current systems by providing an abstract and non-specialized data model and query language for the representation and manipulation of spatial objects. DEDALE relies on a logical model based on linear constraints, which generalizes the constraint database model of(More)
We study the complexity of two central XML processing problems. The first is XPath 1.0 query processing, which has been shown to be in PTIME in previous work. We prove that both the data complexity and the query complexity of XPath 1.0 fall into lower (highly parallelizable) complexity classes, while the combined complexity is PTIME-hard. Subsequently, we(More)
We consider the navigational core of XPath, extended with two operators: the Kleene star for taking the transitive closure of path expressions, and a subtree relativisation operator, allowing one to restrict attention to a specific subtree while evaluating a subexpression. We show that the expressive power of this XPath dialect equals that of FO(MTC), first(More)