1. Link Analysis on the Web An Example: Broad-topic Queries Xin

2. Problem Specific queries: “Does Netscape support the JDK 1.1 code-signing API?” Broad-topic queries: “Find information about the Java programming language.” Authority is important in broad-topic queries Web Query: “ java ” 1.http://java.sun.comhttp://java.sun.com 2.http://sunsite.unc.edu/java faq/javafaq.htmlhttp://sunsite.unc.edu/java faq/javafaq.html 3.…

3. Why to use link analysis comparing to content information? Query: Harvard “Harvard” occurring times: 4 Harvard HomepageOther page introducing Harvard “Harvard” occurring times: 8 Query: Search engines “Search engines” occurring times: 0 Yahoo! HomepageOther page introducing search engines “Search engines” occurring times: 4

4. Graph Presentation G=(V,E) V: pages E: in-link and out-link Adjacency matrix p1p1 p2p2 p3p3 p4p4 p1p1 p2p2 p3p3 p4p4 1 1 1 1 1 Given a query, how to find the most authoritative page through these link information?

5. Overview Web Query: “ java ” 1.http://java.sun.comhttp://java.sun.com 2.http://sunsite.unc.edu/java faq/javafaq.htmlhttp://sunsite.unc.edu/java faq/javafaq.html 3.… 1 2 1.Sub-graph construction 2.Hubs and authorities computation

6. Step1: Sub-graph Construction Challenge: –Small in size –Rich in relevant pages –Contains most of the strongest authorities

7. Step2: Hubs and Authorities Basic Idea: in-degree Problem:

8. Step2: Hubs and Authorities

9. An Iterative Algorithm:

10. Simple Example 1 (x,y): x=hub score y=authority score (1/4,1/4)

11. Simple Example 2 (1/4,1/4) Hub : 1: 1/4 2: 1/4+1/4 3: 1/4 4: 1/4 Authority : 1: 1/4+1/4+1/4 2: 1/4 3: 0 4: 1/4 0

12. Page Rank