NLTK named entity recognition in dutch

Question

I am trying to extract named entities from dutch text. I used nltk-trainer to train a tagger and a chunker on the conll2002 dutch corpus. However, the parse method from the chunker is not detecting any named entities. Here is my code:

str = 'Christiane heeft een lam.'

tagger = nltk.data.load('taggers/dutch.pickle')
chunker = nltk.data.load('chunkers/dutch.pickle')

str_tags = tagger.tag(nltk.word_tokenize(str))
print str_tags

str_chunks = chunker.parse(str_tags)
print str_chunks

And the output of this program:

[('Christiane', u'N'), ('heeft', u'V'), ('een', u'Art'), ('lam', u'Adj'), ('.', u'Punc')]
(S Christiane/N heeft/V een/Art lam/Adj ./Punc)

I was expecting Christiane to be detected as a named entity. Any help?

Answer 1

The conll2002 corpus has both spanish and dutch text, so you should make sure to use the fileids parameter, as in python train_chunker.py conll2002 --fileids ned.train. Training on both spanish and dutch will have poor results.

The default algorithm is a Tagger based Chunker, which does not work well on conll2002. Instead, use a classifier based chunker like NaiveBayes, so the full command might look like this (and I've confirmed that the resulting chunker does recognize "Christiane" as a "PER"):

python train_chunker.py conll2002 --fileids ned.train --classifier NaiveBayes --filename ~/nltk_data/chunkers/conll2002_ned_NaiveBayes.pickle