Link Analysis :
Page rank
PageRank One of the key concepts for improving Web search has been to analyze the hyperlinks and the graph structure of the Web. Such link analysis is one of many factors considered by Web search engines in computing a composite score for a Web page on any given query. For the purpose of better search results and especially to make search engines resistant against term spam, the concept of link-based analysis was developed. Here, the Web is treated as one giant graph: The Web page being a node and edges being links pointing to this Web page. Following this concept, the number of inbound links for a Web page gives a measure of its importance. Hence, a Web page is generally more important if many other Web pages link to it. Google, the pioneer in the field of search engines, came up with two innovations based on link analysis to combat term spam: 1. Consider a random surfer who begins at a Web page (a node of the Web graph) and executes a random walk on the Web as follows. At each time step, the surfer proceeds from his current page A to a randomly chosen Web page that A has hyperlinks to. As the surfer proceeds in this random walk from node to node, some nodes will be visited more often than others; intuitively, these are nodes with many links coming in from other frequently visited nodes. As an extension to this idea, consider a set of such random surfers and after a period of time find which Web pages had large number of surfers visiting it. The idea of PageRank is that pages with large number of visits are more important than those with few visits. 2. The ranking of a Web page is not dependent only on terms appearing on that page, but some weightage is also given to the terms used in or near the links to that page. This helps to avoid term spam because even though a spammer may add false terms to one Website, it is difficult to identify and stuff keywords into pages pointing to a particular Web page as that Web page may not be owned by the spammer.
PageRank Definition PageRank is a link analysis function which assigns a numerical weighting to each element of a hyperlinked set of documents, such as the WWW. PageRank helps in “measuring” the relative importance of a document (Web page) within a set of similar entities. The numerical weight that it assigns to any given element E is referred to as the PageRank of E and denoted by PR(E). The PageRank value of a Web page indicates its importance − higher the value more relevant is this Webpage. A hyperlink to a page counts as a vote of support. The PageRank of a page is defined recursively and depends on the number and PageRank metric of all pages that link to it (“incoming links”). A page that is linked to by many pages with high PageRank receives a high rank itself.
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