Tree automata and logic programs
Each clause of a definite sentence can be read as a move of a tree automaton. These tree automata, called pattern replacing automata (PRA), are introduced and studied in this paper.
Each PRA (and hence each definite sentence) can be put into particularly simple forms ; for definite sentences these special forms are as follows : (1) in each clause the premise contains all the variables of the conclusion ; (2) in each clause all variables of the premise appear also in the conclusion ; and (3) in each clause the height of the terms of the premise is one at most and the height of the terms of the conclusion is two at most.
The class of tree languages recognized by a restricted class of PRA, called monadic weak PRA, coincides with the class of recognizable tree languages.
The rest of the paper consists of two sections. In section 1 we shortly give the necessary definitions and in section 2 we intuitively explain the results mentioned above.
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- K.R. Apt and M.H. Van Emden; Contributions to the theory of logic programming; JACM, vol. 29 (1982), 841–862.Google Scholar
- J. Engelfriet; Tree automata and tree grammars; University of Aarhus, DAIMI FN-10, 1975.Google Scholar
- J. E. Hopcroft and J. D. Ullman; "Formal languages and their relation to automata"; Addison Wesley Pub. Co., Reading, Ma., 1969.Google Scholar
- G. Marque-Pucheu; Rational set of trees and the algebraic semantics of logic programming; Acta Informatica 20 (1983), 249–260.Google Scholar