After crawling and keyword indexing, the next wave that has made a significant impact on Web search is topic distillation: analyzing properties of the hyperlink graph for enhanced ranking of Web pages in response to a query. Hyperlink induced topic search (HITS) and PageRank (used in Google) are two examples. The linear algebra involved in HITS and PageRank is standard, but selecting the relevant subgraph of the Web to which these algorithms should be applied is considerably less clear.

more »

... was intended for the entire Web graph (or as much as a crawler can collect) whereas HITS used keyword match followed by a distance-one graph expansion to determine the relevant subgraph.