See slide #5 onwards of: http://www.cis.upenn.edu/~bcpierce/papers/harmonyslides-2003aug.pdf http://www.cis.upenn.edu/~bcpierce/papers/harmonyslides-2003... I

See slide #5 onwards of: http://www.cis.upenn.edu/~bcpierce/papers/harmonyslides-2003aug.pdf http://www.cis.upenn.edu/~bcpierce/papers/harmonyslides-2003... It explains the terms and explores the pros and cons of each approach.