Package nltk :: Package tag :: Module brill :: Class ProximateTokensTemplate

type ProximateTokensTemplate

    object --+    
             |    
BrillTemplateI --+
                 |
                ProximateTokensTemplate

An brill templates that generates a list of ProximateTokensRules that apply at a given sentence position. In particular, each ProximateTokensTemplate is parameterized by a proximate token brill rule class and a list of boundaries, and generates all rules that:

use the given brill rule class
use the given list of boundaries as the start and end points for their conditions
are applicable to the given token.

Instance Methods

[hide private]

__init__(self, rule_class, *boundaries)
Construct a template for generating proximate token brill rules.

source code

list of BrillRule

applicable_rules(self, tokens, index, correct_tag)
Return a list of the transformational rules that would correct the ith subtoken's tag in the given token. source code

_applicable_conditions(self, tokens, index, start, end)
Returns: A set of all conditions for proximate token rules that are applicable to tokens[index], given boundaries of (start, end). source code

Set

get_neighborhood(self, tokens, index)
Returns the set of indices i such that applicable_rules(token, i, ...) depends on the value of the indexth subtoken of token. source code

Method Details

[hide private]

init(self, rule_class, boundaries)
(Constructor)*

source code

Construct a template for generating proximate token brill rules.

Parameters:

rule_class (class) - The proximate token brill rule class that should be used to generate new rules. This class must be a subclass of ProximateTokensRule.
boundaries (tuple of (int, int)) - A list of tuples (start, end), each of which specifies a range for which a condition should be created by each rule.

Raises:

ValueError - If start>end for any boundary.

Overrides: BrillTemplateI.__init__

applicable_rules(self, tokens, index, correct_tag)

source code

Return a list of the transformational rules that would correct the ith subtoken's tag in the given token. In particular, return a list of zero or more rules that would change tagged_tokens[i][1] to correctTag, if applied to token.

If the ith subtoken already has the correct tag (i.e., if tagged_tokens[i][1] == correctTag), then applicable_rules should return the empty list.

Parameters:

tokens - The tagged tokens being tagged.
i - The index of the token whose tag should be corrected.
correctTag - The correct tag for the ith token.

Returns: list of BrillRule

Overrides: BrillTemplateI.applicable_rules

(inherited documentation)

_applicable_conditions(self, tokens, index, start, end)

source code

Returns:: A set of all conditions for proximate token rules that are applicable to tokens[index], given boundaries of (start, end). I.e., return a list of all tuples (start, end, value), such the property value of at least one token between index+start and index+end (inclusive) is value.

get_neighborhood(self, tokens, index)

source code

Returns the set of indices i such that applicable_rules(token, i, ...) depends on the value of the indexth subtoken of token.

This method is used by the "fast" Brill tagger trainer.

Parameters:

token - The tokens being tagged.
index - The index whose neighborhood should be returned.

Returns: Set

Overrides: BrillTemplateI.get_neighborhood

(inherited documentation)

type ProximateTokensTemplate

__init__(self, rule_class, *boundaries) (Constructor)

applicable_rules(self, tokens, index, correct_tag)

_applicable_conditions(self, tokens, index, start, end)

get_neighborhood(self, tokens, index)

init(self, rule_class, boundaries)
(Constructor)*