nltk.parse.pchart

module documentation
(source)

Classes and interfaces for associating probabilities with tree structures that represent the internal organization of a text. The probabilistic parser module defines BottomUpProbabilisticChartParser.

BottomUpProbabilisticChartParser is an abstract class that implements a bottom-up chart parser for PCFG grammars. It maintains a queue of edges, and adds them to the chart one at a time. The ordering of this queue is based on the probabilities associated with the edges, allowing the parser to expand more likely edges before less likely ones. Each subclass implements a different queue ordering, producing different search strategies. Currently the following subclasses are defined:

  • InsideChartParser searches edges in decreasing order of their trees' inside probabilities.
  • RandomChartParser searches edges in random order.
  • LongestChartParser searches edges in decreasing order of their location's length.

The BottomUpProbabilisticChartParser constructor has an optional argument beam_size. If non-zero, this controls the size of the beam (aka the edge queue). This option is most useful with InsideChartParser.

Class BottomUpProbabilisticChartParser An abstract bottom-up parser for PCFG grammars that uses a Chart to record partial results. BottomUpProbabilisticChartParser maintains a queue of edges that can be added to the chart. This queue is initialized with edges for each token in the text that is being parsed...
Class InsideChartParser A bottom-up parser for PCFG grammars that tries edges in descending order of the inside probabilities of their trees. The "inside probability" of a tree is simply the probability of the entire tree, ignoring its context...
Class LongestChartParser A bottom-up parser for PCFG grammars that tries longer edges before shorter ones. This sorting order results in a type of best-first search strategy.
Class ProbabilisticBottomUpInitRule Undocumented
Class ProbabilisticBottomUpPredictRule Undocumented
Class ProbabilisticFundamentalRule Undocumented
Class ProbabilisticLeafEdge Undocumented
Class ProbabilisticTreeEdge Undocumented
Class RandomChartParser A bottom-up parser for PCFG grammars that tries edges in random order. This sorting order results in a random search strategy.
Class SingleEdgeProbabilisticFundamentalRule Undocumented
Class UnsortedChartParser A bottom-up parser for PCFG grammars that tries edges in whatever order.
Function demo A demonstration of the probabilistic parsers. The user is prompted to select which demo to run, and how many parses should be found; and then each parser is run on the same demo, and a summary of the results are displayed.
def demo(choice=None, draw_parses=None, print_parses=None): (source) ΒΆ

A demonstration of the probabilistic parsers. The user is prompted to select which demo to run, and how many parses should be found; and then each parser is run on the same demo, and a summary of the results are displayed.