自然语言理解

       声明：代码的运行环境为Python3。Python3与Python2在一些细节上会有所不同，希望广大读者注意。本博客以代码为主，代码中会有详细的注释。相关文章将会发布在我的个人博客专栏《Python自然语言处理》，欢迎大家关注。

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       有了之前的学习之后，就可以进行自然语言的理解分析了，一起来看看吧~

一、基于SQL数据库的问答系统

1、首先输入一个特征文法 

import nltk

# 基于sql数据库的问答系统
nltk.data.show_cfg('grammars/book_grammars/sql0.fcfg')  # 输入一个特征文法

输出结果为：

% start S
S[SEM=(?np + WHERE + ?vp)] -> NP[SEM=?np] VP[SEM=?vp]
VP[SEM=(?v + ?pp)] -> IV[SEM=?v] PP[SEM=?pp]
VP[SEM=(?v + ?ap)] -> IV[SEM=?v] AP[SEM=?ap]
NP[SEM=(?det + ?n)] -> Det[SEM=?det] N[SEM=?n]
PP[SEM=(?p + ?np)] -> P[SEM=?p] NP[SEM=?np]
AP[SEM=?pp] -> A[SEM=?a] PP[SEM=?pp]
NP[SEM='Country="greece"'] -> 'Greece'
NP[SEM='Country="china"'] -> 'China'
Det[SEM='SELECT'] -> 'Which' | 'What'
N[SEM='City FROM city_table'] -> 'cities'
IV[SEM=''] -> 'are'
A[SEM=''] -> 'located'
P[SEM=''] -> 'in'

2、将询问的语句转换为一个可用于数据库查询的SQL语句

from nltk import load_parser
# 将正常的询问语句转化为正常的SQL语句
cp = load_parser('grammars/book_grammars/sql0.fcfg')
query = 'What cities are located in China'
trees = list(cp.parse(query.split()))
answer = trees[0].label()['SEM']
answer = [s for s in answer if s]
q = ' '.join(answer)
print(q)

输出结果为：

SELECT City FROM city_table WHERE Country="china"

3、测试

from nltk.sem import chat80

rows = chat80.sql_query('corpora/city_database/city.db', q)
for r in rows:
    print(r[0], " ")

输出结果为：

canton  
chungking  
dairen  
harbin  
kowloon  
mukden  
peking  
shanghai  
sian  
tientsin  

       这里有必要说明一下，这个输出结果为粤语的拼音，故而感觉起来有点怪怪的~由上例可以看出，只要我们定义了一个文法，我们就可以将一个问题提取转换成一个正常的可用于数据库查询的SQL语句。

二、命题逻辑

1、使用boolean_ops()方法进行表示

nltk.boolean_ops()

negation       	-
conjunction    	&
disjunction    	|
implication    	->
equivalence    	<->

运算符为true的条件如下图所示：

2、测试

read_expr = nltk.sem.Expression.fromstring
read_expr('-(P & Q)')
read_expr('P & Q')
read_expr('P | (R -> Q)')
read_expr('P <-> -- P')

最后一个的结果：

 --P)>

测试： 

lp = nltk.sem.Expression.fromstring
SnF = read_expr('SnF')
NotFnS = read_expr('-FnS')
R = read_expr('SnF -> -FnS')
prover = nltk.Prover9()
prover.config_prover9(r'D:\Program Files\LADR1007B-win\bin')
prover.prove(NotFnS, [SnF, R])

val = nltk.Valuation([('P', True), ('Q', True), ('R', False)])
print(val['P'])

结果：

True

dom = set()
g = nltk.Assignment(dom)
m = nltk.Model(dom, val)
print(m.evaluate('(P & Q)', g))
print(m.evaluate('-(P & Q)', g))
print(m.evaluate('(P & R)', g))
print(m.evaluate('(P | R)', g))

True
False
False
True

三、一阶逻辑

# 一阶逻辑
read_expr = nltk.sem.Expression.fromstring
expr = read_expr('walk(angus)', type_check=True)
print(expr.argument)
print(expr.argument.type)
print(expr.function)
print(expr.function.type)

结果为：

angus
e
walk

sig = {'walk': ''}
expr = read_expr('walk(angus)', signature=sig)
print(expr.function.type)

read_expr = nltk.sem.Expression.fromstring
read_expr('dog(cyril)').free()
read_expr('dog(x)').free()
read_expr('own(angus, cyril)').free()
read_expr('exists x.dog(x)').free()
read_expr('((some x. walk(x)) -> sing(x))').free()
read_expr('exists x.own(y, x)').free()

真值模型：

# 真值模型
dom = {'b', 'o', 'c'}
v = """
bertie => b
olive => o
cyril => c
boy => {b}
girl => {o}
dog => {c}
walk => {o, c}
see => {(b, o), (c, b), (o, c)}
"""
val = nltk.Valuation.fromstring(v)
print(val)
print(('o', 'c') in val['see'])
print(('b',) in val['boy'])

运算：

# 运算
g = nltk.Assignment(dom, [('x', 'o'), ('y', 'c')])
print(g)

m = nltk.Model(dom, val)
m.evaluate('see(olive, y)', g)
print(g['y'])

m.evaluate('see(y, x)', g)
g.purge()
print(g)
m.evaluate('see(olive, y)', g)
m.evaluate('see(bertie, olive) & boy(bertie) & -walk(bertie)', g)

四、量化

m.evaluate('exists x.(girl(x) & walk(x))', g)

m.evaluate('girl(x) & walk(x)', g.add('x', 'o'))

fmla1 = read_expr('girl(x) | boy(x)')
m.satisfiers(fmla1, 'x', g)
fmla2 = read_expr('girl(x) -> walk(x)')
m.satisfiers(fmla2, 'x', g)
fmla3 = read_expr('walk(x) -> girl(x)')
m.satisfiers(fmla3, 'x', g)

m.evaluate('all x.(girl(x) -> walk(x))', g)

五、量化歧义

v2 = """
bruce => b
elspeth => e
julia => j
matthew => m
person => {b, e, j, m}
admire => {(j, b), (b, b), (m, e), (e, m)}
"""
val2 = nltk.Valuation.fromstring(v2)

dom2 = val2.domain
m2 = nltk.Model(dom2, val2)
g2 = nltk.Assignment(dom2)
fmla4 = read_expr('(person(x) -> exists y.(person(y) & admire(x, y)))')
m2.satisfiers(fmla4, 'x', g2)

fmla5 = read_expr('(person(y) & all x.(person(x) -> admire(x, y)))')
m2.satisfiers(fmla5, 'y', g2)

fmla6 = read_expr('(person(y) & all x.((x = bruce | x = julia) -> admire(x, y)))')
m2.satisfiers(fmla6, 'y', g2)

六、句子语义理解

read_expr = nltk.sem.Expression.fromstring
expr = read_expr(r'\x.(walk(x) & chew_gum(x))')
print(expr)

expr.free()

print(read_expr(r'\x.(walk(x) & chew_gum(y))'))

expr = read_expr(r'\x.(walk(x) & chew_gum(x))(gerald)')
print(expr)
print(expr.simplify())

print(read_expr(r'\x.\y.(dog(x) & own(y, x))(cyril)').simplify())
print(read_expr(r'\x y.(dog(x) & own(y, x))(cyril, angus)').simplify())

expr1 = read_expr('exists x.P(x)')
print(expr1)

expr2 = expr1.alpha_convert(nltk.sem.Variable('z'))
print(expr2)

print(expr1 == expr2)

expr3 = read_expr('\P.(exists x.P(x))(\y.see(y, x))')
print(expr3)

print(expr3.simplify())

七、量词歧义

from nltk.sem import cooper_storage as cs

sentence = 'every girl chases a dog'
trees = cs.parse_with_bindops(sentence, grammar='grammars/book_grammars/storage.fcfg')
semrep = trees[0].label()['SEM']
cs_semrep = cs.CooperStore(semrep)
print(cs_semrep.core)

for bo in cs_semrep.store:
    print(bo)

cs_semrep.s_retrieve(trace=True)

for reading in cs_semrep.readings:
    print(reading)

八、段落语义理解

read_dexpr = nltk.sem.DrtExpression.fromstring
drs1 = read_dexpr('([x, y], [angus(x), dog(y), own(x, y)])')
print(drs1)

drs1.draw()

print(drs1.fol())

drs2 = read_dexpr('([x], [walk(x)]) + ([y], [run(y)])')
print(drs2)

print(drs2.simplify())

drs3 = read_dexpr('([], [(([x], [dog(x)]) -> ([y],[ankle(y), bite(x, y)]))])')
print(drs3.fol())

drs4 = read_dexpr('([x, y], [angus(x), dog(y), own(x, y)])')
drs5 = read_dexpr('([u, z], [PRO(u), irene(z), bite(u, z)])')
drs6 = drs4 + drs5
print(drs6.simplify())

print(drs6.simplify().resolve_anaphora())

from nltk import load_parser

parser = load_parser('grammars/book_grammars/drt.fcfg', logic_parser=nltk.sem.drt.DrtParser())
trees = list(parser.parse('Angus owns a dog'.split()))
print(trees[0].label()['SEM'].simplify())