document: Dynamic maintenance of web indexes using landmarks Recent work on incremental crawling has enabled the indexed document collection of a search engine to be more synchronized with the changing World Wide Web . However , this synchronized collection is not immediately searchable , because the keyword index is rebuilt from scratch less frequently than the collection can be refreshed . An inverted index is usually used to index documents crawled from the web . Complete index rebuild at high frequency is expensive . Previous work on incremental inverted index updates have been restricted to adding and removing documents . Updating the inverted index for previously indexed documents that have changed has not been addressed . In this paper , we propose an efficient method to update the inverted index for previously indexed documents whose contents have changed . Our method uses the idea of landmarks together with the diff algorithm to significantly reduce the number of postings in the inverted index that need to be updated . Our experiments verify that our landmark-diff method results in significant savings in the number of update operations on the inverted index .
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