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.
In REF it was shown that it is decidable in polynomial time for queries defined by deterministic nested word automata, whether the maximal number of concurrently alive candidates is bounded.
Bounded delay and concurrency for earliest query answering
In LATA, 2009. RR n° 7812 Karanasos, Katsifodimos, Manolescu & Zoupanos
Computer Science