From Word Automata to Tree Automata

Finite tree automata have now become a live research field both because of its features as a theoretical model of computation and its practical value in the parsing, query and verification of semi-structured data, such as XML. The aim of this work is to create a link between the already well-developed finite state automata over words and the finite automata over trees, by adding the mechanism of "invocation-and-return\´\´ to a group of finite word automata. In this paper, the definition of this link and the resulted computation model, recursive tree automata, are formalized based on former works. Then we present an analysis for its expressiveness, closure properties and decision problems, to show that a group of finite word automata armed with this link has identical power of a tree automata. Also some applications of this link are introduced, involving a means of formalization of the W3C XML Schema.