A few more details about Google’s possible analysis of page text
is now available thanks to a recently published patent
application by Googler Anna Patterson from June 2006. The
application details how a search engine like Google might
analyze text phrases, date-based topics, and associate a web
page with related topics, even if the specific topic does not
appear in the document itself. The 22-page document further
emphasizes Google’s current work on “shingle” analysis to
discover important phrases and concepts. (via Search Engine
Land) Highly ranked websites are more likely to receive in-depth
analysis through multiple index passes and phrase associations.
Factors such as PageRank, count weights, and type weights might
grant a page admission to further analysis and a secondary
relevance index based on phrase data. The phrase indexer passes
over a document to determine key phrases and contextual themes
throughout. If your web page contains references to a specific
date the indexer might limit its vocabulary t