If there is something new, the index created will also be updated. They will check if there are any changes made to the web pages from time to time. You can take the index as a huge database of words and where they appear on different pages.Ĭrawlers won't stop completely once they have indexed web pages.

After the data on the page is captured, the words on the page will be placed into the index of a search engine. When web crawlers visit a certain page, it goes through all the content of the page and then conveys it to its database. By constant visiting, web crawlers can discover new pages or URLs, update changes to existing pages, as well as mark those dead links. During the visits, it will also look for other related websites that worth a visit. To elaborate, a web crawler starts its work by visiting a list of websites that it has visited before. Add those new URLs to the related candidate.Extract the URLs among the associated web pages.Download other related and associated web pages.Select a URL from a group of candidates.Here are the major steps executed by a web crawler: When you search 'big data' on a certain search engine, the search will check its index and return findings for you. To put it simply, the index is a list of words as well as the web pages related to those words. Crawlers will build a big index to include all the findings. The crawler will go through many web pages to check the words on the page and where the words are used in other places. Let's take the search engine crawler as an example. Generally, a web crawler is like an online librarian who indexes websites to update web information and evaluate the quality of the web page content. You may also wonder how a web crawler works. Now, you have a basic idea about what a web crawler is. Do you ever wonder what makes search engines go around and work? With web crawlers, search engines can present relevant web pages results responding to users' search inputs. The most famous web crawler is Googlebot. Web crawlers are operated frequently by search engines, such as Google and Yahoo. It is called a web crawler because crawling is a term to describe the behavior of automatically accessing websites and acquiring data through scraping tools. To give you a precise definition of a web crawler, it is an Internet bot, also known as web spider, automatic indexer, web robot, that automatically scans information through the Web to create an index of the data. Speaking of web crawlers, what comes to your mind? A spider crawling on spiderwebs? That's what actually a web crawler does.

Google web crawler