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Machine Learning Summer School 2006 - Taipei
Pascal

Large Scale Ranking Problem: some theoretical and algorithmic issues

author: Tong Zhang, Yahoo! Research, Yahoo!

Description

The talk is divided into two parts. The first part focuses on web-search ranking, for which I discuss training relevance models based on DCG (discounted cumulated gain) optimization. Under this metric, the system output quality is naturally determined by the performance near the top of its rank-list. I will mainly focus on various theoretical issues for this learning problem. The second part discusses related algorithmic issues in the context of optimizing the scoring function of a statistical machine translation system according to the BLEU metric (standard measure of translation quality). Our approach treats machine translation as a black-box, and can optimize millions of system parameters automatically. This has not been attempted before in this context. I will present our method and some initial results.

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Slides
0:05 Advertizing
2:04 Ranking Problems
4:06 Earlier Work on Statistical Ranking
7:38 Theoretical Results on Ranking
9:39 Web-Search Problem
12:32 Relevance Ranking: Statistical Learning Formulation
13:49 Measuring Ranking Quality
15:23 Subset Ranking Model
16:40 Some Theoretical Questions
17:42 Bayes Optimal Scoring
18:36 Simple Regression
20:38 Importance Weighted Regression
22:11 Relationship of Regression and Ranking
22:58 Appropriate Parameter Choice (for previous Theorem)
23:03 Generalization Performance with Square Regularization
23:41 Interpretation of Results
24:55 Another Ranking Example: spelling correction in
web-search
25:49 Some Conclusions

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