Polynomial-time learning of elementary formal systems

Satoru Miyano, Ayumi Shinohara, Takeshi Shinohara

Research output: Contribution to specialist publicationArticle

25 Citations (Scopus)


An elementary formal system (EFS) is a logic program consisting of definite clauses whose arguments have patterns instead of first-order terms. We investigate EFSs for polynomial-time PAC-learnability. A definite clause of an EFS is hereditary if every pattern in the body is a subword of a pattern in the head. With this new notion, we show that H-EFS(m, k, t, r) is polynomial-time learnable, which is the class of languages definable by EFSs consisting of at most m hereditary definite clauses with predicate symbols of arity at most r, where k and t bound the number of variable occurrences in the head and the number of atoms in the body, respectively. The class defined by all finite unions of EFSs in H-EFS(m, k, t, r) is also polynomial-time learnable. We also show an interesting series of NC-learnable classes of EFSs. As hardness results, the class of regular pattern languages is shown not polynomial-time learnable unless RP = NP. Furthermore, the related problem of deciding whether there is a common subsequence which is consistent with given positive and negative examples is shown NP-complete.

Original languageEnglish
Number of pages26
Specialist publicationNew Generation Computing
Publication statusPublished - 2000


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