Decision problems of tree transducers with origin

Abstract

A tree transducer with origin translates an input tree into a pair of output tree and origin information. The origin information maps each node in the output tree to the unique node in the input tree that created it. In this way, the implementation of the transducer becomes part of its semantics. We show that the landscape of decidable properties changes drastically when origin information is added. For instance, equivalence of nondeterministic top-down and MSO transducers with origin becomes decidable. Both problems are undecidable without origin. The equivalence of deterministic top-down tree-to-string transducers is decidable with origin, while without origin it has (until very recently) been a long standing open problem. With origin, we can decide if a deterministic macro tree transducer can be realized by a deterministic top-down tree transducer; without origin this is an open problem.