Showing papers on "Indexed language published in 2009"
01 Jul 2009
TL;DR: A pumping lemma of the usual universal form for the subclass consisting of well-nested multiple context-free languages, which is the same class of languages generated by non-duplicating macro grammars and by coupled-context-free Grammars.
Abstract: Seki et al. (1991) proved a rather weak pumping lemma for multiple context-free languages, which says that any infinite m-multiple context-free language contains a string that is pumpable at some 2m substrings. We prove a pumping lemma of the usual universal form for the subclass consisting of well-nested multiple context-free languages. This is the same class of languages generated by non-duplicating macro grammars and by coupled-context-free grammars.
46 citations
TL;DR: It is shown that the pumping lemma in L-valued regular languages (L-RLs) more recently established by the second author is generalized.
33 citations
Journal Article•
TL;DR: Derivations using branch-interchanging and language family obtained by context-free and interchange (AB → BA) rules are analyzed and semi-linear languages can be generated in this way.
Abstract: Derivations using branch-interchanging and language family obtained by context-free and interchange (AB → BA) rules are analyzed. This language family is between the context-free and context-sensitive families. Closure properties and other properties are detailed. Only semi-linear languages can be generated in this way. Relation to partial commutations is shown.
14 citations
20 Aug 2009
TL;DR: For any given grammar, the class of languages recognized by automata generated by all its synchronized grammars is considered, which forms an effective boolean algebra lying between the classes of regular languages and unambiguous context-free languages.
Abstract: Functional graph grammars are finite devices which generate the class of regular automata We recall the notion of synchronization by grammars, and for any given grammar we consider the class of languages recognized by automata generated by all its synchronized grammars The synchronization is an automaton-related notion: all grammars generating the same automaton synchronize the same languages When the synchronizing automaton is unambiguous, the class of its synchronized languages forms an effective boolean algebra lying between the classes of regular languages and unambiguous context-free languages We additionally provide sufficient conditions for such classes to be closed under concatenation and its iteration
6 citations
12 Aug 2009
TL;DR: It is proved an interesting result that all these families of contextual languages are incomparable to each other, but they are not disjoint.
Abstract: In the recent years, several new classes of contextual grammars have been introduced to give an appropriate model description to natural languages. With this aim, some new families of contextual languages have been introduced based on maximal and depth-first conditions and analyzed in the framework of so-called mildly context sensitive languages. However, the relationship among these families of languages have not yet been analyzed in detail. In this paper, we investigate the relationship between the families of languages whose grammars are based on maximal and depth-first conditions. We prove an interesting result that all these families of languages are incomparable to each other, but they are not disjoint.
1 citations