xử lý ngôn ngữ tự nhiên,kai wei chang,www cs virginia edu Lecture 13 Structured Prediction Kai Wei Chang CS @ University of Virginia kw@kwchang net Couse webpage http //kwchang net/teaching/NLP16 1CS6[.]
Lecture 13: Structured Prediction Kai-Wei Chang CS @ University of Virginia kw@kwchang.net Couse webpage: http://kwchang.net/teaching/NLP16 CS6501: NLP CuuDuongThanCong.com https://fb.com/tailieudientucntt Quiz v Lectures 9-13 v Lecture 12: before page 44 v Lecture 13: before page 33 v Key points: v HMM model v Three basic problems v Sequential tagging CS6501: NLP CuuDuongThanCong.com https://fb.com/tailieudientucntt Three basic problems for HMMs v Likelihood of the input: v Forward algorithm How likely the sentence ”I love cat” occurs v Decoding (tagging) the input: v Viterbi algorithm POS tags of ”I love cat” occurs v Estimation (learning): How to learn the model? v Find the best model parameters v Case 1: supervised – tags are annotated vMaximum likelihood estimation (MLE) v Case 2: unsupervised only unannotated text vForward-backward algorithm CS6501: NLP CuuDuongThanCong.com https://fb.com/tailieudientucntt Supervised Learning Setting v Assume we have annotated examples Tag set: DT, JJ, NN, VBD… POS Tagger The/DT grand/JJ jury/NN commented/VBD on/IN a/DT number/NN of/IN other/JJ topics/NNS / CS6501: NLP CuuDuongThanCong.com https://fb.com/tailieudientucntt Sequence tagging problems v Many problems in NLP (ML) have data with tag sequences v Brainstorm: name other sequential tagging problems CS6501: NLP CuuDuongThanCong.com https://fb.com/tailieudientucntt OCR example CS6501: NLP CuuDuongThanCong.com https://fb.com/tailieudientucntt Noun phrase (NP) chunking v Task: identify all non-recursive NP chunks CS6501: NLP CuuDuongThanCong.com https://fb.com/tailieudientucntt The BIO encoding v Define three new tags v B-NP: beginning of a noun phrase chunk v I-NP: inside of a noun phrase chunk v O: outside of a noun phrase chunk POS Tagging with a restricted Tagset? CS6501: NLP CuuDuongThanCong.com https://fb.com/tailieudientucntt Shallow parsing v Task: identify all non-recursive NP, verb (“VP”) and preposition (“PP”) chunks CS6501: NLP CuuDuongThanCong.com https://fb.com/tailieudientucntt BIO Encoding for Shallow Parsing v Define new tags v B-NP B-VP B-PP: beginning of an “NP”, “VP”, “PP” chunk v I-NP I-VP I-PP: inside of an “NP”, “VP”, “PP” chunk v O: outside of any chunk POS Tagging with a restricted Tagset? CS6501: NLP CuuDuongThanCong.com 10 https://fb.com/tailieudientucntt ... VBD… POS Tagger The/DT grand/JJ jury/NN commented/VBD on/IN a/DT number/NN of/IN other/JJ topics/NNS / CS6 501: NLP CuuDuongThanCong.com https://fb.com/tailieudientucntt Sequence tagging problems... sequences v Brainstorm: name other sequential tagging problems CS6 501: NLP CuuDuongThanCong.com https://fb.com/tailieudientucntt OCR example CS6 501: NLP CuuDuongThanCong.com https://fb.com/tailieudientucntt... POS Tagging with a restricted Tagset? CS6 501: NLP CuuDuongThanCong.com https://fb.com/tailieudientucntt Shallow parsing v Task: identify all non-recursive NP, verb (“VP”) and preposition (“PP”) chunks CS6 501: NLP CuuDuongThanCong.com