Search Engine - Document Reprensentation and Index

When we talk about search engine, we actually talk about one form of information retrieval systems. Web pages as documents, and web search engine gives us results based on our query. The idea seems simple, but how does search engine get this job done in millisecond? The number of web pages could be as high as 180 quadrillion! Before going deep into this, first we would like to know the representation of web pages in search engine, and we start with a simple document retrieval. »