class POS_decoder(Model1):
TUNE_POS_WEIGHT = 2
def __init__(self, parameter_file):
super(POS_decoder,self).__init__(parameter_file)
self.tagger = PosTagger()
def get_parallel_instance(self, corpus_line):
(german, english) = corpus_line.strip().split(' ||| ')
return ([word for word in german.split(" ")],
[word for word in english.split(" ")])
def get_prior(self, **features):
"""
returns 1+TUNE_POS_WEIGHT if the POS tags are aligned else 1
"""
return 1+self.TUNE_POS_WEIGHT*(
features.get("tag_german",self.null_val)==features.get("tag_english",self.null_val))
def get_alignment(self, german, english):
"""
Returns Model1 alignment for a DE/EN parallel sentence pair.
For each german word, identifies the best english word (or NULL) to align to
Applies a prior which assigns higher probability to alignments which preserve POS tags.
"""
alignment = []
gtags = self.tagger.parse(german,"de")
etags = self.tagger.parse(english,"en")
(german,english) = ([self.get_german_stem(word).lower() for word in german],
[self.get_english_stem(word).lower() for word in english])
etags.append(self.null_val)
english.append(self.null_val)
for (i, g_i) in enumerate(german):
best = -1
bestscore = 0
for (j, e_j) in enumerate(english):
val = self.get_prior(tag_german=gtags[i],tag_english=etags[j])*\
self.get_translation_prob(g_i,e_j)
if best==-1 or val>bestscore:
bestscore = val
best = j
if best < len(english)-1:
yield (i,best) # don't yield anything for NULL alignment
def __init__(self, parameter_file):
super(POS_decoder,self).__init__(parameter_file)
self.tagger = PosTagger()
