Multiple Context-Free Grammars
نویسنده
چکیده
Multiple context-free grammar (MCFG) is a weakly contextsensitive grammar formalism that deals with tuples of strings. An MCFG is called m-MCFG if all tuples have at most m components. In this summary I will outline that the expressivity of m-MCFG’s increases with the parameter m and that the class of tree-adjoining languages is properly included in the class of 2-multiple context-free languages. In addition, I will give a brief overview over the parsing complexity of m-MCFG’s. 1 Generalized context-free grammars Multiple context-free grammars are a restricted form of generalized context-free grammars. Generalized context-free grammar is a grammar formalism that deals with tuples of strings. Rewriting rules in generalized context-free grammars have the form A→ f [B, B, . . . , B] where A and B, . . . , B are nonterminal symbols and f is a partial function whose arguments and function values are tuples of strings. Formally, a generalized context-free grammar is defined as follows. Definition 1. A generalized context-free grammar (GCFG) is a 5-tuple G = (N,O,F, P, S). – N is a finite set of nonterminal symbols. – O is a set of n-tuples (n ≥ 1) over a finite set of symbols. – F is a finite set of partial functions from O × · · · ×O to O. – P is a finite set of rewriting rules. – S ∈ N is the start symbol. The rewriting rules contained in P are written as A→ f [B, B, . . . , B] where A ∈ N and B, B, . . . , B ∈ N are nonterminal symbols and f ∈ F is a function from O to O. A rewriting rule is called terminating rule, if q = 0 holds, i.e. there is no terminal symbol in the right-hand side of this rewriting rule. In this case, the rewriting-rule is written as
منابع مشابه
Multiple Context Free Grammars
Multiple context-free grammars (MCFGs) are a generalization of context-free grammars that deals with tuples of strings. This is a brief survey of MCFGs, their properties, and their relations to other formalisms. We outline simple constructions to convert MCFGs to Hyperedge Replacement Grammars (HRGs) and to Deterministic Tree Walking Transducers (DTWTs), and also to simulate DTWTs by MCFGs. We ...
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