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The cached document is the latest snapshot of the page that the search engine has seen. In addition to indexing pages, search engines may also store a highly compressed text-only version of a document including all HTML and metadata. This example uses URLs but these might be document IDs instead depending on how the search engine is structured. In the example you can see that each keyword (or token) is associated with a row of documents in which that element was identified. An example of inverted indexingīelow is a very basic example which illustrates the concept of inverted indexing. This is a much faster approach than listing all known documents against all relevant keywords and characters. Then, search engines use a process called tokenisation to reduce words to their core meaning, thus reducing the amount of resources needed to store and retrieve data. Instead, search engines (including Google) use an inverted index, also known as a reverse index.Īn inverted index is a system wherein a database of text elements is compiled along with pointers to the documents which contain those elements. Searching through individual pages for keywords and topics would be a very slow process for search engines to identify relevant information. Indexing is the process by which search engines organise information before a search to enable super-fast responses to queries. Search engines have revolutionised information retrieval to the extent that users expect near-instantaneous responses to their search queries. Remember the days before the internet when you’d have to consult an encyclopedia to learn about the world and dig through the Yellow Pages to find a plumber? Even in the early days of the web, before search engines, we had to search through directories to retrieve information. What’s the need for indexing by search engines? What happens once a search engine has finished crawling a page? Let’s take a look at the indexing process that search engines use to store information about web pages, enabling them to quickly return relevant, high quality results.