What does “Index” mean in search engine?
Index can be called the place for categorizing data, which is used to speed up the search process. Suppose that there is no index process, search engine would have to go through every document while searching the result. It can cause a lot of memory usage and the search time would be longer.
For example, how do you place the book called Cinderella in the library? If you put the book whatever you want, it would be very hard to find the book later because there are a lot of books. However, if you put the book in novel section, it could be faster to find it. Like this, indexing is the process of storing the data onto specific place for search later.
There are a lot of designs or architectures for indexing data in every search engine. Apache Lucene, which is open source search engine has data structure called inverted index. Moreover, Apache Solr, Elasticsearch wihch are based on Apache Lucene got the same structure as well.
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