Characterization of Context-Free Languages with Polynomially Bounded Ambiguity
نویسنده
چکیده
We prove that the class of context-free languages with polynomially bounded ambiguity (PCFL) is the closure of the class of unambiguous languages (UCFL) under projections which deletes Parikh bounded symbols only. A symbol a is Parikh bounded in a language L if there is a constant c such that no word of L contains more than c occurrences of a. Furthermore PCFL is closed under the formally stronger operation of Parikh bounded substitution, i.e., a substitution which is the identity for non Parikh bounded symbols. Finally we prove that the closure of UCFL under union and concatenation is a proper subset of
منابع مشابه
On the unary equivalence of stochastic languages and stochastic context-free languages
We show that every unary stochastic context-free grammar with polynomially bounded ambiguity, has an equivalent probabilistic automaton.
متن کاملOn the Circuit Complexity of Random Generation Problems for Regular and Context-Free Languages
We study the circuit complexity of generating at random a word of length n from a given language under uniform distribution. We prove that, for every language accepted in polynomial time by 1-NAuxPDA of polynomially bounded ambiguity, the problem is solvable by a logspace-uniform family of probabilistic boolean circuits of polynomial size and O(log2 n) depth. Using a suitable notion of reducibi...
متن کاملExtending Parikh's Theorem to Weighted and Probabilistic Context-Free Grammars
We prove an analog of Parikh’s theorem for weighted context-free grammars over commutative, idempotent semirings, and exhibit a stochastic context-free grammar with behavior that cannot be realized by any stochastic right-linear context-free grammar. Finally, we show that every unary stochastic context-free grammar with polynomially-bounded ambiguity has an equivalent stochastic right-linear co...
متن کاملParikh’s Theorem for Weighted and Probabilistic Context-Free Grammars
We prove an analog of Parikh’s theorem for weighted context-free grammars over commutative, idempotent semirings, and exhibit a stochastic context-free grammar with behavior that cannot be realized by any stochastic right-linear context-free grammar. Finally, we show that every unary stochastic context-free grammar with polynomially-bounded ambiguity has an equivalent stochastic right-linear co...
متن کاملSublinear Ambiguity
A context-free grammar G is ambiguous if there is a word that can be generated by G with at least two different derivation trees. Ambiguous grammars are often distinguished by their degree of ambiguity, which is the maximal number of derivation trees for the words generated by them. If there is no such upper bound G is said to be ambiguous of infinite degree. By considering how many derivation ...
متن کاملذخیره در منابع من
با ذخیره ی این منبع در منابع من، دسترسی به آن را برای استفاده های بعدی آسان تر کنید
عنوان ژورنال:
دوره شماره
صفحات -
تاریخ انتشار 2001