Package nltk :: Package parse :: Module chart :: Class TreeEdge

Class TreeEdge

object --+    
         |    
     EdgeI --+
             |
            TreeEdge

Known Subclasses:

An edge that records the fact that a tree is (partially) consistent with the sentence. A tree edge consists of:

A span, indicating what part of the sentence is consistent with the hypothesized tree.
A left-hand side, specifying the hypothesized tree's node value.
A right-hand side, specifying the hypothesized tree's children. Each element of the right-hand side is either a terminal, specifying a token with that terminal as its leaf value; or a nonterminal, specifying a subtree with that nonterminal's symbol as its node value.
A dot position, indicating which children are consistent with part of the sentence. In particular, if dot is the dot position, rhs is the right-hand size, (start,end) is the span, and sentence is the list of subtokens in the sentence, then subtokens[start:end] can be spanned by the children specified by rhs[:dot].

For more information about edges, see the EdgeI interface.

Instance Methods

[hide private]

__init__(self, span, lhs, rhs, dot=0)
Construct a new TreeEdge. source code

lhs(self)
Returns: This edge's left-hand side, which specifies what kind of structure is hypothesized by this edge.

source code

(int, int)

span(self)
Returns: A tuple (s,e), where subtokens[s:e] is the portion of the sentence that is consistent with this edge's structure. source code

int

start(self)
Returns: The start index of this edge's span.

source code

int

end(self)
Returns: The end index of this edge's span.

source code

int

length(self)
Returns: The length of this edge's span.

source code

rhs(self)
Returns: This edge's right-hand side, which specifies the content of the structure hypothesized by this edge.

source code

int

dot(self)
Returns: This edge's dot position, which indicates how much of the hypothesized structure is consistent with the sentence.

source code

boolean

is_complete(self)
Returns: True if this edge's structure is fully consistent with the text.

source code

boolean

is_incomplete(self)
Returns: True if this edge's structure is partially consistent with the text.

source code

Nonterminal or terminal or None

next(self)
Returns: The element of this edge's right-hand side that immediately follows its dot.

source code

__cmp__(self, other)

source code

__hash__(self)
hash(x)

source code

__str__(self)
str(x)

source code

__repr__(self)
repr(x)

source code

Inherited from object: __delattr__, __getattribute__, __new__, __reduce__, __reduce_ex__, __setattr__

Static Methods

[hide private]

TreeEdge

from_production(production, index)
Returns: A new TreeEdge formed from the given production.

Properties

[hide private]

Inherited from object: __class__

Method Details

[hide private]

init(self, span, lhs, rhs, dot=0)
(Constructor)

source code

Construct a new TreeEdge.

Parameters:

span ((int, int)) - A tuple (s,e), where subtokens[s:e] is the portion of the sentence that is consistent with the new edge's structure.
lhs (Nonterminal) - The new edge's left-hand side, specifying the hypothesized tree's node value.
rhs (list of (Nonterminal and string)) - The new edge's right-hand side, specifying the hypothesized tree's children.
dot (int) - The position of the new edge's dot. This position specifies what prefix of the production's right hand side is consistent with the text. In particular, if sentence is the list of subtokens in the sentence, then subtokens[span[0]:span[1]] can be spanned by the children specified by rhs[:dot].

Overrides: EdgeI.__init__

from_production(production, index)
Static Method

Returns: TreeEdge: A new TreeEdge formed from the given production. The new edge's left-hand side and right-hand side will be taken from production; its span will be (index, index); and its dot position will be 0.

lhs(self)

source code

Returns:: This edge's left-hand side, which specifies what kind of structure is hypothesized by this edge.
Overrides: EdgeI.lhs: (inherited documentation)

span(self)

source code

Returns: (int, int): A tuple (s,e), where subtokens[s:e] is the portion of the sentence that is consistent with this edge's structure.
Overrides: EdgeI.span: (inherited documentation)

start(self)

source code

Returns: int: The start index of this edge's span.
Overrides: EdgeI.start: (inherited documentation)

end(self)

source code

Returns: int: The end index of this edge's span.
Overrides: EdgeI.end: (inherited documentation)

length(self)

source code

Returns: int: The length of this edge's span.
Overrides: EdgeI.length: (inherited documentation)

rhs(self)

source code

Returns:: This edge's right-hand side, which specifies the content of the structure hypothesized by this edge.
Overrides: EdgeI.rhs: (inherited documentation)

dot(self)

source code

Returns: int: This edge's dot position, which indicates how much of the hypothesized structure is consistent with the sentence. In particular, self.rhs[:dot] is consistent with subtoks[self.start():self.end()].
Overrides: EdgeI.dot: (inherited documentation)

is_complete(self)

source code

Returns: boolean: True if this edge's structure is fully consistent with the text.
Overrides: EdgeI.is_complete: (inherited documentation)

is_incomplete(self)

source code

Returns: boolean: True if this edge's structure is partially consistent with the text.
Overrides: EdgeI.is_incomplete: (inherited documentation)

next(self)

source code

Returns: Nonterminal or terminal or None: The element of this edge's right-hand side that immediately follows its dot.
Overrides: EdgeI.next: (inherited documentation)