Ordering Constraints over Feature Trees Expressed in Second-order Monadic Logic
Résumé
The system FT< of ordering constraints over feature trees has been introduced as an extension of the system FT of equality constraints over feature trees. While the first-order theory of FT is well understood, only few complexity and decidability results are known for fragments of the first-order theory of FT<. We introduce a new handle for such decidability questions by showing how to express ordering constraints over feature trees in second-order monadic logic (S2S or WS2S). Our relationship implies a new decidability result for feature logics, namely that the entailment problem of FT< with existential quantifiers P |= models exists x1 ... exists xn P' is decidable. We also show that this problem is PSPACE-hard even though the quantifier-free case can be solved in cubic time. To our knowledge, this is the first time that a non-trivial decidability result of feature logic is reduced to Rabins famous tree theorem.
Origine | Fichiers produits par l'(les) auteur(s) |
---|
Loading...