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Bounded delay and concurrency for earliest query answering
 In LATA, 2009. RR n° 7812 Karanasos, Katsifodimos, Manolescu & Zoupanos
"... Abstract. Earliest query answering is needed for streaming XML processing with optimal memory management. We study the feasibility of earliest query answering for node selection queries. Tractable queries are distinguished by a bounded number of concurrently alive answer candidates at every time poi ..."
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Abstract. Earliest query answering is needed for streaming XML processing with optimal memory management. We study the feasibility of earliest query answering for node selection queries. Tractable queries are distinguished by a bounded number of concurrently alive answer candidates at every time point, and a bounded delay for node selection. We show that both properties are decidable in polynomial time for queries defined by deterministic automata for unranked trees. Our results are obtained by reduction to the bounded valuedness problem for recognizable relations between unranked trees. 1
Regular nary queries in trees and variable independence
 in: International Conference on Theoretical Computer Science (IFIP TCS), 2008
"... Summary. Regular nary queries in trees are queries which are definable by an MSO formula with n free firstorder variables. We investigate the variable independence problem – originally introduced for databases – in the context of trees. In particular, we show how to decide whether a regular query ..."
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Summary. Regular nary queries in trees are queries which are definable by an MSO formula with n free firstorder variables. We investigate the variable independence problem – originally introduced for databases – in the context of trees. In particular, we show how to decide whether a regular query is equivalent to a union of cartesian products, independently of the input tree. As an intermediate step, we reduce this problem to the problem of deciding whether the number of answers to a regular query is bounded by some constant, independently of the input tree. As a (nontrivial) generalization, we introduce variable independence w.r.t. a dependence forest between blocks of variables, which we prove to be decidable. 1