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A web crawler is an automated program that searches through internet pages to create an index of data. It is commonly used by search engines, linguists, and market researchers. The crawler reads visible text, hyperlinks, and tags to determine the site’s content and is programmed for long-term use. It can periodically scan the internet for changes and revisit sites if necessary. Illegal uses include hacking into servers for more information.
A web crawler is a relatively simple automated program, or script, that methodically crawls or “crawls” through Internet pages to create an index of the data it is looking for; these programs are generally designed for one-time use, but can also be programmed for long-term use. There are several uses for the program, perhaps the most popular being that search engines use it to provide surfers with relevant websites. Other users include linguists and market researchers or anyone looking for information from the Internet in an organized way. Alternative names for a web crawler include web spider, web robot, bot, crawler, and auto indexer. Crawler programs can be purchased on the Internet or from many companies that sell computer software, and the programs can be downloaded onto most computers.
Common uses
There are various uses for web crawlers, but essentially a web crawler can be used by anyone trying to gather information on the internet. Search engines often use web crawlers to gather information about what is available on public web pages. Their main purpose is to collect data so that when Internet surfers enter a search term on their site, they can quickly provide the surfer with relevant websites. Linguists can use a web crawler to perform text analysis; that is, they can scour the Internet to determine which words are commonly used today. Market researchers can use a web crawler to determine and evaluate trends in a given market.
Web crawling is an important method of gathering data and keeping pace with the rapidly expanding Internet. A vast number of web pages are continuously being added every day and the information is constantly changing. A web crawler is a way for search engines and other users to regularly make sure their databases are up to date. There are a number of illegal uses of web crawlers, such as hacking into a server to get more information than is freely provided.
How does it work?
When a search engine’s web crawler visits a web page, it “reads” visible text, hyperlinks, and the content of various tags used on the site, such as keyword-rich meta tags. Using the information gathered by the crawler, a search engine will then determine what the site is about and index the information. The website is then included in the search engine’s database and its page ranking process.
Web crawlers can only operate once, such as for a particular one-time project. If its purpose is long-term, as is the case with search engines, web crawlers can be programmed to periodically scan the Internet to determine if there have been any significant changes. If a site is experiencing heavy traffic or technical difficulties, the spider can be programmed to notice and revisit the site again, hopefully after the technical problems have subsided.
