1. Person Name Disambiguation by Bootstrapping Presenter: Lijie Zhang Advisor: Weining Zhang

2. Outlines Introduction Motivation Two-stage Clustering Algorithm Experiments

3. People Name Disambiguation Given a target name (query q ), search engine returns a set of web pages P={ d 1, d 2, …, d n } Task: cluster web pages P such that each cluster refers to a single person.

4. Example: People Name Disambiguation

5. People Name Disambiguation A typical solution:  Extract a set of features from each document returned by search engine  Cluster the documents based on some similarity metrics on sets of features Two types of features  Strong features such as named entities (NEs), compound key words (CKWs), URLs NE: Paul Allen, Microsoft (indicate the person Bill Gates) CKW: chief software architect (a concept strongly related to Bill Gates) Very strong ability to distinguish between clusters.  Weak features: single words

6. People Name Disambiguation Evaluation Metric: F measure  Treat each cluster as if it were the result of a query and each class as if it were the desired set of documents for a query  For class i and cluster j, Recall(i, j)= n ij /n i, Precision(i, j)=n ij /n j F(i, j) = (2 * Recall(i, j) * Precision(i, j)) / ((Precision(i, j) + Recall(i, j))

7. Motivation Problem of current systems: Using only strong features achieves high precision but low recall. Proposed solution: two-stage clustering algorithm by bootstrapping to improve the recall value.  1 st stage: strong features  2 nd stage: weak features

8. Two-stage Clustering Algorithm Input: one query string Output: a set of clusters 1. Preprocessing documents returned by search engine 2. First-stage clustering 3. Second-stage clustering

9. Preprocessing a Document Covert HTML files to text files  Remove HTML tags  Keep sentences Extract text around query string  Using a window size Extract strong features (NEs, CKWs, URLs)

10. Extract Strong Features Use Stanford NER to identify NEs:  a set of sets of names including names of persons, organizations, and places Compound Key Word (CKW) Features: a set of CKWs  Extract compound words (CW): w 1 w 2..w l  Score each CW:  Determine CKW based on a threshold of scores. Extract URLs from the original HTML files  exclude URLs with high frequencies

11. Two-stage Clustering Algorithm Input: one or more query strings Output: a set of clusters 1. Preprocessing documents returned by search engine 2.1 st stage clustering 3. 2 nd stage clustering

12. First stage clustering 1. Calculate the similarities between documents based on these features 2. Use standard hierarchical agglomerative clustering (HAC) algorithm for clustering

13. Document Similarities Similarity for NE features and CKW features  avoids too small denominator values in the equation

14. Document Similarities Similarity for URLs

15. Document Similarities Similarity for NE: Similarities for NE, CKW, and URL

16. First stage clustering 1. Calculate the similarities between documents based on these features 2. Use standard hierarchical agglomerative clustering (HAC) algorithm for clustering

17. HAC algorithm Starts from one-in-one clustering, i.e. each document is a cluster Iteratively merge the most similar cluster pairs, which similarity is above a threshold. Cluster similarity:

18. Two-stage Clustering Algorithm Input: one or more query strings Output: a set of clusters 1. Preprocessing documents returned by search engine 2.1 st stage clustering 3. 2 nd stage clustering

19. Second Stage Clustering Goal: Cluster documents still in one-in-one clustering after the first stage clustering Idea of bootstrapping algorithm:  Given some seed instances, finds patterns useful to extract such seed instances;  Use these patterns to harvest new instances, and form the harvested new instances new patterns are induced. Instances correspond to documents Patterns correspond to weak features: 1-gram, 2-gram in experiment

20. Second Stage Clustering

22. Experiments Setup Dataset: WePS-2  30 names, each has 150 pages  The same page can refer to two or more entities; Evaluation Metrics [5]  Multiplicity precision and recall between document e and e’ C(e) is predicted cluster of e, L(e) is the cluster assigned to e by the gold standard

23. Example of Evaluation Metrics L(1)={A,B} L(2)={A,B} C(1)={ct1, ct2} C(2)={ct1, ct2} L(1)={A,B} L(2)={A,B} C(1)={ct1} C(2)={ct1, ct2} L(1)={A,B} L(2)={A,B} C(1)={ct1,ct2,ct3} C(2)={ct1, ct2,ct3}

24. Experiments Setup Evaluation Metrics  Extended B-Cubed precision (BEP) and recall (BER)

25. Experiments Setup Baselines:  First stage clustering: all-in-one, one-in-one, combined baseline (each doc belongs to one cluster from all-in-one and one from one-in- one).  Second stage clustering: TOPIC algorithm, CKW algorithm

26. Experiments Results

27. References [1] A. Bagga and B. Baldwin. Entity-based cross-document coreferencing using the vector space model. In Proceedings of COLING-ACL 1998, pages 79–85, 1998. [2] C. Niu, W. Li, and R. K. Srihari. Weakly supervised learning for cross-document person name disambiguation supported by information extraction. In Proceedings of 42nd Annual Meeting of the Association for Computational Linguistics (ACL-2004), pages 598–605, 2004. [3] X. Liu, Y. Gong, W. Xu, and S. Zhu. Document clustering with cluster refinement and model selection capabilities. In Proceedings of the 25th annual international ACM SIGIR conference on Research and development in information retrieval, pages 191– 198, 2002. [4] X. Wan, M. L. J. Gao, and B. Ding. Person resolution in person search results: WebHawk. In Proceedings of CIKM2005, pages 163–170, 2005. [5] E. Amigo, J. Gonzalo, J. Artiles, and F. Verdejo. A comparison of extrinsic clustering evaluation metrics based on formal constraints. Information Retrieval, 12(4), 2009. [6] Minoru Yoshida, Masaki Ikeda, Shingo Ono, Issei Sato, Hiroshi Nakagawa. Person Name Disambiguation by Bootstrapping. In Proceedings of SIGIR, 2010.