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Problem 1: Word Segmentation
whatdoesthisreferto
what does this refer to
Application: Chinese Text
Application: Internet Domain Names
www.visitbritain.com
Visit Britain
Statistical Machine Learning
Best segmentation= one with highest probability
Probability of a segmentation= P(first word) × P(rest of segmentation)
P(word)= estimated by counting
Statistical Machine Learning
choosespain
Choose Spain Chooses pain
P(“Choose Spain”) > P(“Chooses Pain”)
Example
segment(“nowisthetime…”) Pf(“n”) × Pr(“owisthetime…”)
Pf(“no”) × Pr(“wisthetime…”)
Pf(“now”) × Pr(“isthetime…”)
Pf(“nowi”) × Pr(“sthetime…”) ……
Example
segment(“nowisthetime…”)
The Complete Program
Performance
Accuracy = 98% Trained on 1.7B words (English)
Typical errors: baseratesoughtto
base rate sought to smallandinsignificant
small and in significant ginormousego
g in or mouse go
Some Results
whorepresents.com[“who”, “represents”]
therapistfinder.com[“therapist”, “finder”]
expertsexchange.com[“experts”, “exchange”]
speedofart.net[“speed”, “of”, “art”]
penisland.com error: expected [“pen”, “island”]
Problem 2: Spelling Correction
Mehran Salami Typical word processor: Tehran Salami But Google can …
Statistical Machine Learning
Best correction= one with highest probability
Probability of a spelling correction c= P(c as a word) × P(original is a typo for c)
P(c as a word)= estimated by counting
P(original is a typo for c)= proportional to number of changes
The Complete Program
Problem 3: Speech Recognition
An informal, incomplete grammar of the English language runs over 1,700 pages.
Invariably, simple models and a lot of data trump more elaborate models based on less data.
Problem 3: Speech Recognition
If you have a lot of data, memorisation is a good policy.
For many tasks such as speech recognition, once we have a billion or so examples, we essentially have a closed set that represents (or at least approximates) what we need, without general rules.
Problem 3: Speech Recognition
Problem 3: Speech Recognition
Problem 3: Speech Recognition
“Every time I fire a linguist, the performance of our speech recognition system goes up.”
--- Fred Jelinek
Problem 4: Machine Translation
Conclusion
(Statistical) [Machine] Learning Is
The Ultimate Agile Development Tool
Peter Norvig(Director of Research, Google)