Nonlinear Tree Pattern Pushdown Automata

A new kind of an acyclic pushdown automaton for an ordered tree is presented. The nonlinear tree pattern pushdown automaton represents a complete index of the tree for nonlinear tree patterns and accepts all nonlinear tree patterns which match the tree. Given a tree with n nodes, the number of such nonlinear tree patterns is O((2+ v)n), where v is the number of variables in the patterns. We discuss time and space complexities of the nondeterministic nonlinear tree pattern pushdown automaton and a way of its implementation. The presented pushdown automaton is input–driven and therefore can be determinised.