Alphabetic Pushdown Tree Transducers
We introduce the concept of an alphabetic pushdown tree transducer, by adding a stack to an alphabetic tree transducer in the same way as a pushdown tree automaton is obtained from a top-down tree automaton. The stack of the general model contains trees, however, we also consider a restricted model of which the stack contains only unary trees. We give a characterization of the tree transformation induced by a restricted alphabetic pushdown tree transducer in terms of an algebraic forest over a suitable ranked alphabet and a bimorphism. We compare the class of tree relations induced by the alphabetic pushdown tree transducers with known classes of tree transformations. Finally, a new hierarchy of tree relations is established.
KeywordsTree Relation Restricted Model Tree Automaton Tree Language Algebraic Characterization
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