We study the sofic tree shifts of A ∗ , where Σ∗ is a regular rooted tree of finite rank. In particular, we give their characterization in terms of unrestricted Rabin automata. We show that if X ⊂ A ∗ is a sofic tree shift, then the configurations in X whose orbit under the shift action is finite are dense in X , and, as a consequence of this, we deduce that every injective cellular automata τ ...

Pebble tree-walking automata with alternation were first investigated by Milo, Suciu and Vianu (2003), who showed that tree languages recognized by these devices are exactly the regular tree languages. We strengthen this by proving the same result for pebble automata with “strong pebble handling” which means that pebbles can be lifted independently of the position of the reading head and withou...

We consider several questions about monotone AC-tree automata, a class of equational tree automata [21] whose transition rules correspond to rules in Kuroda normal form of context-sensitive grammars. Whereas it is known that this class has a decision procedure to determine if a given monotone AC-tree automaton accepts no term [23], other decidability and complexity results have not been well-in...

This paper presents new classes of tree automata combining automata with equality test with automata modulo equational theories. These tree automata are obtained by extending their standard Horn clause representations with equational conditions and monadic rewrite systems. We show in particular that the general membership problem is decidable by proving that the saturation of tree automata pres...

We address the problem of tight XML schemas and propose regular tree automata to model XML data. We show that the tree automata model is more powerful that the XML DTDs and is closed under main algebraic operations. We introduce the XML query algebra based the tree automata model, and discuss the query optimization and query pruning techniques. Finally, we show the conversion of tree automata s...