Search Engine limitations
What is the size of the Web?
1 trillion (as in 1,000,000,000,000) unique URLs on the web.
March 1, 2013: Google says that the web now has 30 trillion unique individual pages.
The estimates vary from 15 to some 30 billion Web pages.
Additionally, the different search engine services have some overlap with each other, and there exist pages and Web sites not indexed by any of them.
Some search engines are designed to build a database of specialized information, such as medical or legal Web sites and Web pages.
Search engines search databases that are filled with words and document addresses, but that doesn't mean they have the intelligence to know what those words mean or in what context they're used.
Searching for documents that contain the word "theater" won't find documents containing any related words, such as "play."
On the other hand, if you're searching for documents containing the word "play," your results could easily include documents that contain the word play in the context of a "sports play" or "games children play."