What is the difference between crawling and Indexing?

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Crawling means sucking content without processing the results. Crawlers are rather dumb processes that fetch content supplied by Web servers answering (HTTP) requests of requested URIs, delivering those contents to other processes, e.g. crawling caches or directly to indexers. Crawlers get their URIs from a crawling engine that’s feeded from different sources, including links extracted from previously crawled Web documents, URI submissions, foreign Web indexes, and whatnot.

Indexing means making sense out of the retrieved contents, storing the processing results in a (more or less complex) document index. Link analysis is a way to measure URI importance, popularity, trustworthiness and so on. Link analysis is often just a helper within the indexing process, sometimes the end in itself, but traditionally a task of the indexer, not the crawler (high sophisticated crawling engines do use link data to steer their crawlers, but that has nothing to do with link analysis in document indexes).