search engine indexing the world wide web contains huge collection of text documents (web pagesinformation about these pages are gathered by program called web crawlerwhich then stores this information in special dictionary database web search engine allows users to retrieve relevant information from this databasethereby identifying relevant pages on the web containing given keywords in this sectionwe present simplified model of search engine inverted files the core information stored by search engine is dictionarycalled an inverted index or inverted filestoring key-value pairs (wl)where is word and is collection of pages containing word the keys (wordsin this dictionary are called index terms and should be set of vocabulary entries and proper nouns as large as possible the elements in this dictionary are called occurrence lists and should cover as many web pages as possible we can efficiently implement an inverted index with data structure consisting of the following an array storing the occurrence lists of the terms (in no particular order compressed trie for the set of index termswhere each leaf stores the index of the occurrence list of the associated term the reason for storing the occurrence lists outside the trie is to keep the size of the trie data structure sufficiently small to fit in internal memory insteadbecause of their large total sizethe occurrence lists have to be stored on disk with our data structurea query for single keyword is similar to wordmatching query (section namelywe find the keyword in the trie and we return the associated occurrence list when multiple keywords are given and the desired output are the pages containing all the given keywordswe retrieve the occurrence list of each keyword using the trie and return their intersection to facilitate the intersection computationeach occurrence list should be implemented with sequence sorted by address or with mapto allow efficient set operations in addition to the basic task of returning list of pages containing given keywordssearch engines provide an important additional service by ranking the pages returned by relevance devising fast and accurate ranking algorithms for search engines is major challenge for computer researchers and electronic commerce companies