Tech Review AI: Tuesday, June 12, 2012

https://class.coursera.org/nlp/lecture/preview

• Have listen to the course introduction
• listening to the Basic Text Processing -> Regular Expressions
• Regular expressions
• a formal language for specifying text strings
• regular expression disjuctions
• letters inside square brackets []
• pipe disjunction
• a|b|c is the same as [abc]
• ranges [A-Z]
• negations [^A-Z]
• ?
• previous character is optional
• .
• one charater
• ^
• begining of line
• $ 
• end of line
• \.
• use backslach to find special characters
• Kleene operators
• Stephen C Kleene
• * is 0 or more
• + is 1 or more
• non-alphabetics 
• regexpal.com
• Type1 error false positive
• increasing accuracy or precision (minimizing false positives)
• Type2 error false negatives
• increasing coverage or recall (minimizing false negatives)
• Type1 and 2 conflict, antagonistic 
• regular expressions play a surprisingly large role in NLP.
• regular expression used as features in classifiers for the hard NLP tasks
• Basic Text Processing -> Regular expression in practical NLP
• Christopher Manning
• Stanford English Tokenizer
• a deterministic
• Java Flexer 
• {2,4}
• length between 2 to 4