Spider (crawler, bot, robot) is an internet-based software application that primarily surfs the world wide web for indexing web content. In short, these bots help search engines to index web content from other sites updated. This aims to create a more effective and efficient search for internet users. Spiders visit web pages without approval and create can load these systems. In accessing a large number of pages, spiders have to consider issues like politeness, schedule, and load. Hence, a site that does not like the visit of spiders on their pages has mechanisms in place to alert crawling agents.
Usually, this gets done by including a robot.txt file that asks spiders to index specific sections or a website or exempt a page entirely. The number of pages on the internet are massive. Therefore no matter how large a crawler is, they aren’t capable of completely indexing all. Due to this, delivering relevant search results in the early years of the worldwide web posed a significant challenge to search engines. However, advances in the technological advancement of today help relevant results almost instantaneously.
A spider or web crawler begins its task with a list of URLs called seeds. It visits this list and finds the total number of hyperlinks at these addresses. The spider then adds these new hyperlinks to the original list of URLs. We term this new list of URLs as the crawl frontier. Spiders then visit URLs belonging to crawl frontier repeatedly per specific policies or rules. If these visits intend to archive the websites, the search engine bot copies and saves the information along the way. Spider, in addition to these uses, can also be used to scrape the web and validate HTML code or hyperlinks.
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