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Web mining slides
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- 2. Web Mining Outline •Goal – – Examine the use of data mining on the World Wide Web. • Outline - – Introduction. – Web Content Mining. – Web Structure Mining. – Web Usage Mining. Mahavir Advaya - Ruia College 2
- 3. Web Mining Issues •Size – – >350 million pages (1999). – Grows at about 1 million pages a day. – Google indexes 3 billion documents. • Diverse types of data. Mahavir Advaya - Ruia College 3
- 4. Web Data • Web pages. • Intra-page structures. • Inter-page structures. • Usage data. • Supplemental data – – Profiles. – Registration information. – Cookies. Mahavir Advaya - Ruia College 4
- 5. Web Mining Taxonomy Mahavir Advaya - Ruia College 5
- 6. Web Content Mining •Extends work of basic search engines. • Search Engines – – IR application. – Keyword based. – Similarity between query and document. – Crawlers. – Indexing. – Profiles. – Link analysis. Mahavir Advaya - Ruia College 6
- 7. Crawlers (Spider) • Robot(spider), a program, traverses the hypertext structure in the Web. – Collect information from visited pages. – Used to construct indexes for search engines. • Traditional Crawler – visits entire Web (?) and replaces index. • Periodic Crawler – visits portions of the Web and updates subset of index. • Incremental Crawler – selectively searches the Web and incrementally modifies index. • Focused Crawler – visits pages related to a particular subject. Mahavir Advaya - Ruia College 7
- 8. Focused Crawler • Onlyvisit links from a page if that page is determined to be relevant. • Classifier is static after learning phase. • Components – – Hypertext Classifier which assigns relevance score to each page based on crawl topic. – Distiller to identify hub pages. – Crawler visits pages to based on crawler and distiller scores. Mahavir Advaya - Ruia College 8
- 9. Focused Crawler • Classifierto related documents to topics. • Classifier also determines how useful outgoing links are. • Hub Pages contain links to many relevant pages. Must be visited even if not high relevance score. Mahavir Advaya - Ruia College 9
- 10. Focused Crawler Mahavir Advaya - Ruia College 10
- 11. Context Focused Crawler • Context Graph – – Context graph created for each seed document . – Root is the seed document. – Nodes at each level show documents with links to documents at next higher level. – Updated during crawl itself . • Approach – 1. Construct context graph and classifiers using seed documents as training data. 2. Perform crawling using classifiers and context graph created. Mahavir Advaya - Ruia College 11
- 12. Context Graph Mahavir Advaya - Ruia College 12
- 13. Virtual Web View •Approach to handle unstructured data. • Multiple Layered DataBase (MLDB) built on top of the Web. • Each layer of the database is more generalized (and smaller) and centralized than the one beneath it. • Upper layers of MLDB are structured and can be accessed with SQL type queries. • Does not require the use of spiders (Crawlers). • Translation tools convert Web documents to XML. • Extraction tools extract desired information to place in first layer of MLDB. Convert web document to XML. • Higher levels contain more summarized data obtained through generalizations of the lower levels. Mahavir Advaya - Ruia College 13
- 14. WebML • Web dataMining Query Language. • Provides data mining operations on MLDB. • Major feature – four operations – – COVERS: one concept covers another if it is higher in the hierarchy. – COVERED BY: reverse of COVERS, reverses the descendents. – LIKE: concept is a synonym. – CLOSE TO: One concept is close to another if it is a sibling in the hierarchy. Mahavir Advaya - Ruia College 14
- 15. WebML • Example – – Find all the documents at the level of www.engr.smu.edu. • Query – SELECT * FROM document in ‘ ‘ www.engr.smu.edu ‘ ‘ WHERE ONE OF keywords COVERS ‘ ‘ cat ‘ ‘ Mahavir Advaya - Ruia College 15
- 16. Personalization • Example ofWeb Content Mining. • Web access or contents tuned to better fit the desires of each user. • With personalization, advertisements to be sent to the customers based on specific knowledge. • Goal – Make the customer purchase something. • Three basic types – – Manual techniques – identify user’s preferences based on profiles or demographics. – Collaborative filtering identifies preferences based on ratings from similar users. – Content based filtering retrieves pages based on similarity between pages and user profiles. Mahavir Advaya - Ruia College 16
- 17. Web Structure Mining •Create a model of the Web organization or a portion of it. • Mine structure (links, graph) of the Web. • Techniques – – PageRank. – CLEVER. • May be combined with content mining to more effectively retrieve important pages. Mahavir Advaya - Ruia College 17
- 18. PageRank • Used byGoogle. • Prioritize pages returned from search by looking at Web structure. • Importance of page is calculated based on number of pages which point to it – Backlinks. • Weighting is used to provide more importance to backlinks coming form important pages. Mahavir Advaya - Ruia College 18
- 19. PageRank (cont’d) • PR(p)= c (PR(1)/N1 + … + PR(n)/Nn) – PR(i): PageRank for a page i which points to target page p. – Ni: number of links coming out of page i. – c: constant value between 0 and 1 used for normalization. Mahavir Advaya - Ruia College 19
- 20. CLEVER • System developedby IBM. • Finding both authoritative and hub pages. • Authoritative Pages – – Authors define an authority as the “best source” for the request. o Highly important pages. o Best source for requested information. • Hub Pages – – Contain links to highly important pages. – Clever, identifies authoritative and hub pages by creating weights. Mahavir Advaya - Ruia College 20
- 21. HITS • Hyperlink-Induces TopicSearch. • Finds Hubs and Authoritative Pages. • Two components – – Based on a set of keywords, find set of relevant pages – R. – Identify hub and authority pages for these. o Expand R to a base set, B, of pages linked to or from R. o Calculate weights for authorities and hubs. • Pages with highest ranks in R are returned. Mahavir Advaya - Ruia College 21
- 22. HITS Algorithm Mahavir Advaya - Ruia College 22
- 23. Web Usage Mining •Extends work of basic search engines. • Performs mining on Web usage data or Web logs. • Search Engines – – IR application. – Keyword based. – Similarity between query and document. – Crawlers. – Indexing. – Profiles. – Link analysis. Mahavir Advaya - Ruia College 23
- 24. Web Usage MiningApplications • Personalization – tracking of previously accessed pages. • Determining frequent access behavior for users. • Improve structure of a site’s Web pages. • Aid in caching and prediction of future page references. • Improve design of individual pages. • Improve effectiveness of e-commerce (sales and advertising). • Gathering Statistics – considering accessed pages may or may not be viewed as part web mining . Mahavir Advaya - Ruia College 24
- 25. Web Usage MiningActivities • Preprocessing Web log – – Cleanse. – Remove extraneous information. – Sessionize – o Session: Sequence of pages referenced by one user at a sitting. • Pattern Discovery – – Count patterns that occur in sessions. – Pattern is sequence of pages references in session. – Similar to association rules – o Transaction: session. o Itemset: pattern (or subset). o Order is important. • Pattern Analysis. Mahavir Advaya - Ruia College 25
- 26. ARs in WebMining • Web Mining – – Content. – Structure. – Usage. • Frequent patterns of sequential page references in Web searching. • Uses – – Caching – Clustering users – Develop user profiles – Identify important pages Mahavir Advaya - Ruia College 26
- 27. Web Usage MiningIssues • Identification of exact user not possible. • Exact sequence of pages referenced by a user not possible due to caching. • Session not well defined. • Security, privacy, and legal issues. Mahavir Advaya - Ruia College 27
- 28. Web Log Cleansing •Replace source IP address with unique but non- identifying ID. • Replace exact URL of pages referenced with unique but non-identifying ID. • Delete error records and records containing not page data (such as figures and code). Mahavir Advaya - Ruia College 28
- 29. Sessionizing • Divide Weblog into sessions. • Two common techniques – – Number of consecutive page references from a source IP address occurring within a predefined time interval (e.g. 25 minutes). – All consecutive page references from a source IP address where the interclick time is less than a predefined threshold. Mahavir Advaya - Ruia College 29
- 30. Data Structures • Keeptrack of patterns identified during Web usage mining process. • Common techniques – – Trie. – Suffix Tree. – Generalized Suffix Tree. – WAP Tree. Mahavir Advaya - Ruia College 30
- 31. Trie vs. SuffixTree • Trie – – Rooted tree. – Edges labeled which character (page) from pattern. – Path from root to leaf represents pattern. • Suffix Tree – – Single child collapsed with parent. Edge contains labels of both prior edges. Mahavir Advaya - Ruia College 31
- 32. Trie and SuffixTree A L O G ALOG Mahavir Advaya - Ruia College 32
- 33. Generalized Suffix Tree •Suffix tree for multiple sessions. • Contains patterns from all sessions. • Maintains count of frequency of occurrence of a pattern in the node. • WAP Tree – – Web Access Pattern. – Compressed version of generalized suffix tree. – Tree stores sequences and their counts. Mahavir Advaya - Ruia College 33
- 34. Types of Patterns •Algorithms have been developed to discover different types of patterns. • Properties – – Ordered – Characters (pages) must occur in the exact order in the original session. – Duplicates – Duplicate characters are allowed in the pattern. – Consecutive – All characters in pattern must occur consecutive in given session. – Maximal – Not subsequence of another pattern. Mahavir Advaya - Ruia College 34
- 35. Pattern Types • Association Rules. • Episodes. • Sequential Patterns. • Forward Sequences. • Maximal Frequent Sequences. Mahavir Advaya - Ruia College 35
- 36. Questions??? • Write ashort note on Web Content Mining. • What is Web Mining? Give web mining taxonomy. • What do you mean by Web Usage Mining? Explain rule with examples. • Write a short note on Harvest System. • Define crawler. State and explain different types of crawlers. • Write a short note on crawlers. • Give taxonomy of web mining activities. For what purpose web usage mining is used? What activities are involved in web usage mining? • What do you understand by the term “Web Usage Mining”. • Explain the term crawlers in web mining. • Discuss the importance of establishing a standardized WebML. • Write a short note on web structure mining. Mahavir Advaya - Ruia College 36
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