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177 lines
6.5 KiB
Plaintext
177 lines
6.5 KiB
Plaintext
.. Copyright (C) 2001-2020 NLTK Project
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.. For license information, see LICENSE.TXT
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========
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PropBank
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========
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The PropBank Corpus provides predicate-argument annotation for the
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entire Penn Treebank. Each verb in the treebank is annotated by a single
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instance in PropBank, containing information about the location of
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the verb, and the location and identity of its arguments:
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>>> from nltk.corpus import propbank
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>>> pb_instances = propbank.instances()
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>>> print(pb_instances) # doctest: +NORMALIZE_WHITESPACE
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[<PropbankInstance: wsj_0001.mrg, sent 0, word 8>,
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<PropbankInstance: wsj_0001.mrg, sent 1, word 10>, ...]
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Each propbank instance defines the following member variables:
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- Location information: `fileid`, `sentnum`, `wordnum`
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- Annotator information: `tagger`
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- Inflection information: `inflection`
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- Roleset identifier: `roleset`
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- Verb (aka predicate) location: `predicate`
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- Argument locations and types: `arguments`
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The following examples show the types of these arguments:
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>>> inst = pb_instances[103]
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>>> (inst.fileid, inst.sentnum, inst.wordnum)
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('wsj_0004.mrg', 8, 16)
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>>> inst.tagger
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'gold'
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>>> inst.inflection
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<PropbankInflection: vp--a>
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>>> infl = inst.inflection
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>>> infl.form, infl.tense, infl.aspect, infl.person, infl.voice
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('v', 'p', '-', '-', 'a')
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>>> inst.roleset
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'rise.01'
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>>> inst.predicate
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PropbankTreePointer(16, 0)
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>>> inst.arguments # doctest: +NORMALIZE_WHITESPACE
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((PropbankTreePointer(0, 2), 'ARG1'),
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(PropbankTreePointer(13, 1), 'ARGM-DIS'),
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(PropbankTreePointer(17, 1), 'ARG4-to'),
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(PropbankTreePointer(20, 1), 'ARG3-from'))
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The location of the predicate and of the arguments are encoded using
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`PropbankTreePointer` objects, as well as `PropbankChainTreePointer`
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objects and `PropbankSplitTreePointer` objects. A
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`PropbankTreePointer` consists of a `wordnum` and a `height`:
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>>> print(inst.predicate.wordnum, inst.predicate.height)
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16 0
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This identifies the tree constituent that is headed by the word that
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is the `wordnum`\ 'th token in the sentence, and whose span is found
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by going `height` nodes up in the tree. This type of pointer is only
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useful if we also have the corresponding tree structure, since it
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includes empty elements such as traces in the word number count. The
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trees for 10% of the standard PropBank Corpus are contained in the
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`treebank` corpus:
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>>> tree = inst.tree
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>>> from nltk.corpus import treebank
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>>> assert tree == treebank.parsed_sents(inst.fileid)[inst.sentnum]
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>>> inst.predicate.select(tree)
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Tree('VBD', ['rose'])
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>>> for (argloc, argid) in inst.arguments:
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... print('%-10s %s' % (argid, argloc.select(tree).pformat(500)[:50]))
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ARG1 (NP-SBJ (NP (DT The) (NN yield)) (PP (IN on) (NP (
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ARGM-DIS (PP (IN for) (NP (NN example)))
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ARG4-to (PP-DIR (TO to) (NP (CD 8.04) (NN %)))
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ARG3-from (PP-DIR (IN from) (NP (CD 7.90) (NN %)))
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Propbank tree pointers can be converted to standard tree locations,
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which are usually easier to work with, using the `treepos()` method:
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>>> treepos = inst.predicate.treepos(tree)
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>>> print (treepos, tree[treepos])
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(4, 0) (VBD rose)
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In some cases, argument locations will be encoded using
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`PropbankChainTreePointer`\ s (for trace chains) or
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`PropbankSplitTreePointer`\ s (for discontinuous constituents). Both
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of these objects contain a single member variable, `pieces`,
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containing a list of the constituent pieces. They also define the
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method `select()`, which will return a tree containing all the
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elements of the argument. (A new head node is created, labeled
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"*CHAIN*" or "*SPLIT*", since the argument is not a single constituent
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in the original tree). Sentence #6 contains an example of an argument
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that is both discontinuous and contains a chain:
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>>> inst = pb_instances[6]
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>>> inst.roleset
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'expose.01'
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>>> argloc, argid = inst.arguments[2]
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>>> argloc
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<PropbankChainTreePointer: 22:1,24:0,25:1*27:0>
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>>> argloc.pieces
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[<PropbankSplitTreePointer: 22:1,24:0,25:1>, PropbankTreePointer(27, 0)]
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>>> argloc.pieces[0].pieces
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... # doctest: +NORMALIZE_WHITESPACE
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[PropbankTreePointer(22, 1), PropbankTreePointer(24, 0),
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PropbankTreePointer(25, 1)]
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>>> print(argloc.select(inst.tree))
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(*CHAIN*
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(*SPLIT* (NP (DT a) (NN group)) (IN of) (NP (NNS workers)))
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(-NONE- *))
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The PropBank Corpus also provides access to the frameset files, which
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define the argument labels used by the annotations, on a per-verb
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basis. Each frameset file contains one or more predicates, such as
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'turn' or 'turn_on', each of which is divided into coarse-grained word
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senses called rolesets. For each roleset, the frameset file provides
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descriptions of the argument roles, along with examples.
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>>> expose_01 = propbank.roleset('expose.01')
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>>> turn_01 = propbank.roleset('turn.01')
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>>> print(turn_01) # doctest: +ELLIPSIS
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<Element 'roleset' at ...>
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>>> for role in turn_01.findall("roles/role"):
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... print(role.attrib['n'], role.attrib['descr'])
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0 turner
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1 thing turning
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m direction, location
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>>> from xml.etree import ElementTree
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>>> print(ElementTree.tostring(turn_01.find('example')).decode('utf8').strip())
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<example name="transitive agentive">
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<text>
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John turned the key in the lock.
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</text>
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<arg n="0">John</arg>
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<rel>turned</rel>
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<arg n="1">the key</arg>
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<arg f="LOC" n="m">in the lock</arg>
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</example>
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Note that the standard corpus distribution only contains 10% of the
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treebank, so the parse trees are not available for instances starting
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at 9353:
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>>> inst = pb_instances[9352]
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>>> inst.fileid
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'wsj_0199.mrg'
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>>> print(inst.tree) # doctest: +NORMALIZE_WHITESPACE +ELLIPSIS
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(S (NP-SBJ (NNP Trinity)) (VP (VBD said) (SBAR (-NONE- 0) ...))
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>>> print(inst.predicate.select(inst.tree))
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(VB begin)
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>>> inst = pb_instances[9353]
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>>> inst.fileid
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'wsj_0200.mrg'
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>>> print(inst.tree)
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None
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>>> print(inst.predicate.select(inst.tree))
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Traceback (most recent call last):
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. . .
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ValueError: Parse tree not avaialable
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However, if you supply your own version of the treebank corpus (by
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putting it before the nltk-provided version on `nltk.data.path`, or
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by creating a `ptb` directory as described above and using the
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`propbank_ptb` module), then you can access the trees for all
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instances.
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A list of the verb lemmas contained in PropBank is returned by the
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`propbank.verbs()` method:
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>>> propbank.verbs()
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['abandon', 'abate', 'abdicate', 'abet', 'abide', ...]
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