What is a Web Crawler
A web crawler is also known as web spider. It is a software program that is used to browse or follow the hyperlinks throughout the website for searching purposes. This process is known as Web Crawling or Spidering. It creates an index of the data that it is looking for faster searching purposes. It will create a copy of the all visited pages and when we will visit those pages again, it will help in downloading those pages faster which otherwise would be downloaded slowly on your system. The major search engines like Google have this program that is called as crawler or a Bot too. It browses the web in a systematic and automated manner. There are many purposes for which web crawlers are used but the prime use is to download or to view the pages faster.
It can also be used for the maintenance purposes of the websites. The information which crawler will index and collect will help him to determine that about the website is. The web crawler for the search engine Alta Vista is called Scooter. All the web crawlers should follow and should hold all the rules specified by Standard for Robot Exclusion that is SRE. Scooter, the web crawler for Alta Vista adheres all the rules of SRE. The web crawler also reads the Meta tags specified by the creator of the website and index the information. Not only search engine uses web crawlers, but these are also used by the linguists who want to know that which of the words are used commonly. There are numerous uses of web crawlers.
It may also be used to know the current trends in the market. A crawler needs a web address as a starting point in order to index the information about the website. Then the crawler finds the hyperlink text and Meta tags in all the pages of the website until the text finishes. You need to keep some important points in your mind if you are going to build a search engine. Some of the websites are very large so it can take time to index all the data. Some of the websites change its content frequently. So you will have to take care of this thing too as when to revisit the page again in order to keep the database up to date. You must know HTML if you are about to build a search engine as we will have to tell the crawler about the italic text, simple text, bold text etc.