jurafsky&martin_3rdEd_17 (1).pdf

# 1111 top sdumpedvbd vpdumpedvbd ppintop npbinnn

• 499
• 100% (1) 1 out of 1 people found this document helpful

This preview shows pages 226–228. Sign up to view the full content.

This preview has intentionally blurred sections. Sign up to view the full version.

13.6 P ROBABILISTIC L EXICALIZED CFG S 227 Suppose we were to treat a probabilistic lexicalized CFG like a really big CFG that just happened to have lots of very complex non-terminals and estimate the probabilities for each rule from maximum likelihood estimates. Thus, according to Eq. 13.18 , the MLE estimate for the probability for the rule P(VP(dumped,VBD) ! VBD(dumped, VBD) NP(sacks,NNS) PP(into,P)) would be Count(VP(dumped,VBD) ! VBD(dumped, VBD) NP(sacks,NNS) PP(into,P)) Count(VP(dumped,VBD)) (13.23) But there’s no way we can get good estimates of counts like those in ( 13.23 ) because they are so specific: we’re unlikely to see many (or even any) instances of a sentence with a verb phrase headed by dumped that has one NP argument headed by sacks and a PP argument headed by into . In other words, counts of fully lexicalized PCFG rules like this will be far too sparse, and most rule probabilities will come out 0.
This is the end of the preview. Sign up to access the rest of the document.
• Fall '09

{[ snackBarMessage ]}

### What students are saying

• As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

Kiran Temple University Fox School of Business ‘17, Course Hero Intern

• I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

Dana University of Pennsylvania ‘17, Course Hero Intern

• The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

Jill Tulane University ‘16, Course Hero Intern