Search Algorithm Used for Keyword Search

[Dhiraj R]

Dear Sir,
I'm doing a literature survey on search engines. As Xapian is open source, I think I can get the information required by me. 
I assume that your system builds a list of keywords and tags to every keyword the documents where it can be found. My questions are as follows:
1. What is the search algorithm used for searching the list of keywords that your search engine has?. Is it the binary search algorithm or some enhancement of it using perhaps some additional data structures?2. Are the keywords listed in alphabetical order or in some other order?3. Does search engine like 'google' use only a binary search or any augmented version of binary search for searching the list of keywords that it maintains?
As I could not get these information from anyone, I request you to kindly provide me the above information as I need them for my thesis work.
Thank you.
Sincerely,Dhiraj R
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