  Tree automata based algorithms are essential in many fields in computer
science such as verification, specification, program analysis. They become also
essential for databases with the development of standards such as XML. In this
paper, we define new classes of non deterministic tree automata, namely
residual finite tree automata (RFTA). In the bottom-up case, we obtain a new
characterization of regular tree languages. In the top-down case, we obtain a
subclass of regular tree languages which contains the class of languages
recognized by deterministic top-down tree automata. RFTA also come with the
property of existence of canonical non deterministic tree automata.
