Text Web Mining.ppt

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1、10/6/2018,1,Text & Web Mining,10/6/2018,2,Structured Data,So far we have focused on mining from structured data:,Attribute Value Attribute Value Attribute Value Attribute Value,Outlook Sunny Temperature Hot Windy Yes Humidity High Play Yes,Most data mining involves such data,10/6/2018,3,Complex Data

2、 Types,Increased importance of complex data: Spatial data: includes geographic data and medical & satellite images Multimedia data: images, audio, & video Time-series data: for example banking data and stock exchange data Text data: word descriptions for objects World-Wide-Web: highly unstructured t

3、ext and multimedia data,10/6/2018,4,Text Databases,Many text databases exist in practice News articles Research papers Books Digital libraries E-mail messages Web pages Growing rapidly in size and importance,10/6/2018,5,Semi-Structured Data,Text databases are often semi-structured Example: Title Aut

4、hor Publication_Date Length Category Abstract Content,10/6/2018,6,Handling Text Data,Modeling semi-structured data Information Retrieval (IR) from unstructured documents Text mining Compare documents Rank importance & relevance Find patterns or trends across documents,10/6/2018,7,Information Retriev

5、al,IR locates relevant documents Key words Similar documentsIR Systems On-line library catalogs On-line document management systems,10/6/2018,8,Performance Measure,Two basic measures,All documents,Retrieved documents,Relevant documents,Relevant & retrieved,10/6/2018,9,Retrieval Methods,Keyword-based

6、 IR E.g., “data and mining” Synonymy problem: a document may talk about “knowledge discovery” instead Polysemy problem: mining can mean different things Similarity-based IR Set of common keywords Return the degree of relevance Problem: what is the similarity of “data mining” and “data analysis”,10/6

7、/2018,10,Modeling a Document,Set of n documents and m terms Each document is a vector v in Rm The j-th coordinate of v measures the association of the j-th termHere r is the number of occurrences of the j-th term and R is the number of occurrences of any term.,10/6/2018,11,Frequency Matrix,10/6/2018

8、,12,Similarity Measures,Cosine measure,Dot product,Norm of the vectors,10/6/2018,13,Example,Google search for “association mining” Two of the documents retrieved: Idaho Mining Association: mining in Idaho (doc 1) Scalable Algorithms for Association mining (doc 2) Using only the two terms,10/6/2018,1

9、4,New Model,Add the term “data” to the document model,10/6/2018,15,Frequency Matrix,Will quickly become large,Singular value decomposition can be used to reduce it,10/6/2018,16,Association Analysis,Collect set of keywords frequently used together and find association among them Apply any association

10、 rule algorithm to a database in the formatdocument_id, a_set_of_keywords,10/6/2018,17,Document Classification,Need already classified documents as training set Induce a classification model Any difference from before?,A set of keywords associated with a document has no fixed set of attributes or di

11、mensions,10/6/2018,18,Association-Based Classification,Classify documents based on associated, frequently occurring text patterns Extract keywords and terms with IR and simple association analysis Create a concept hierarchy of terms Classify training documents into class hierarchies Use association

12、mining to discover associated terms to distinguish one class from another,10/6/2018,19,Remember Generalized Association Rules,Clothes,Outerwear,Shirts,Jackets,Ski Pants,Footwear,Shoes,Hiking Boots,Taxonomy:,Generalized association rule X Y where no item in Y is an ancestor of an item in X,Ancestor o

13、f shoes and hiking boots,10/6/2018,20,Classifiers,Let X be a set of terms Let Anc (X) be those terms and their ancestor terms Consider a rule X C and document d If X Anc (d) then X C covers d A rule that covers d may be used to classify d (but only one can be used),10/6/2018,21,Procedure,Step 1: Gen

14、erate all generalized association rules , where X is a set of terms and C is a class, that satisfy minimum support. Step 2: Rank the rules according to some rule ranking criterion Step 3: Select rules from the list,10/6/2018,22,Web Mining,The World Wide Web may have more opportunities for data minin

15、g than any other area However, there are serious challenges: It is too huge Complexity of Web pages is greater than any traditional text document collection It is highly dynamic It has a broad diversity of users Only a tiny portion of the information is truly useful,10/6/2018,23,Search Engines Web M

16、ining,Current technology: search engines Keyword-based indices Too many relevant pages Synonymy and polysemy problems More challenging: web mining Web content mining Web structure mining Web usage mining,10/6/2018,24,Web Content Mining,10/6/2018,25,Example: Classification of Web Documents,Assign a c

17、lass to each document based on predefined topic categories E.g., use Yahoo!s taxonomy and associated documents for training Keyword-based document classification Keyword-based association analysis,10/6/2018,26,Web Structure Mining,10/6/2018,27,Authoritative Web Pages,High quality relevant Web pages

18、are termed authoritative Explore linkages (hyperlinks) Linking a Web page can be considered an endorsement of that page Those pages that are linked frequently are considered authoritative (This has its roots back to IR methods based on journal citations),10/6/2018,28,Structure via Hubs,A hub is a se

19、t of Web pages containing collections of links to authorities There is a wide variety of hubs: Simple list of recommended links on a persons home page Professional resource lists on commercial sites,10/6/2018,29,HITS,Hyperlink-Induced Topic Search (HITS) Form a root set of pages using the query term

20、s in an index-based search (200 pages) Expand into a base set by including all pages the root set links to (1000-5000 pages) Go into an iterative process to determine hubs and authorities,10/6/2018,30,Calculating Weights,Authority weightHub weight,Page p is pointed to by page q,10/6/2018,31,Adjacenc

21、y Matrix,Lets number the pages 1,2,n The adjacency matrix is defined byBy writing the authority and hub weights as vectors we have,10/6/2018,32,Recursive Calculations,We now haveBy linear algebra theory this converges to the principle eigenvectors of the the two matrices,10/6/2018,33,Output,The HITS

22、 algorithm finally outputs Short list of pages with high hub weights Short list of pages with high authority weightsHave not accounted for context,10/6/2018,34,Applications,The Clever Project at IBMs Almaden Labs Developed the HITS algorithmGoogle Developed at Stanford Uses algorithms similar to HIT

23、S (PageRank) On-line version,10/6/2018,35,Web Usage Mining,10/6/2018,36,Complex Data Types Summary,Emerging areas of mining complex data types: Text mining can be done quite effectively, especially if the documents are semi-structured Web mining is more difficult due to lack of such structure Data includes text documents, hypertext documents, link structure, and logs Need to rely on unsupervised learning, sometimes followed up with supervised learning such as classification,