Node Query Preservation for Deterministic Linear Top-Down Tree Transducers

This paper discusses the decidability of node query preservation problems for XML document transformations. We assume a transformation given by a deterministic linear top-down data tree transducer (abbreviated as DLTV ) and an n-ary query based on runs of a tree automaton. We say that a DLTV Tr strongly preserves a query Q if there is a query Q′ such that for every document t, the answer set of Q′ for Tr(t) is equal to the answer set of Q for t. Also we say that Tr weakly preserves Q if there is a query Q′ such that for every td in the range of Tr, the answer set of Q′ for td is equal to the union of the answer set of Q for t such that td = Tr(t). We show that the weak preservation problem is coNP-complete and the strong preservation problem is in 2-EXPTIME.