Spider: The Program Used by Search Engines to Search the Internet for Documents

Introduction:
Search engines are powerful tools that help users find information on the internet. Behind the scenes, these search engines utilize complex programs to crawl and index web pages. One of the key components of this process is the use of a program called a "spider" or a "web crawler."

What is a Spider?
A spider is an automated program used by search engines to systematically browse the internet and collect information from web pages. It starts by visiting a specific web address, commonly known as a URL or Uniform Resource Locator. The spider then analyzes the content of the web page and follows links to other pages on the same website. This process continues recursively, allowing the spider to discover and index a vast number of web pages.

How a Spider Works:
1. Seed URLs: The spider starts with a set of seed URLs, which are typically popular websites or URLs recommended by the search engine's algorithm.
2. Fetching: The spider requests the HTML content of the seed URL from the web server.
3. Parsing: The spider parses the HTML document, extracting various components such as text, links, images, and metadata.
4. Follow Links: The spider identifies all the links within the HTML document and adds them to a list of URLs to visit.
5. URL Queue: The spider maintains a queue of URLs to visit, prioritizing them based on factors like relevance, popularity, or freshness.
6. Recursion: The spider repeats the process for each URL in the queue, visiting the web pages and extracting information.
7. Indexing: As the spider crawls web pages, it collects data and sends it back to the search engine's database for indexing.
8. Continual Crawling: The spider continuously crawls the web, revisiting previously indexed pages to check for updates or changes.

Search Engine Examples:
1. Bing: Bing is a search engine developed by Microsoft. While it uses spiders for crawling, it is not the correct answer in this case.
2. MSN: MSN is a web portal and online service offered by Microsoft. It is not a program used for web crawling.
3. Spider: Spider is the correct answer as it represents the program used by search engines to search the internet for documents.
4. Google: Google is a popular search engine that utilizes spiders to crawl and index web pages.

Conclusion:
In conclusion, the program used by search engines to search the internet for documents using their web addresses is known as a spider. This automated program plays a crucial role in the search engine's ability to discover, analyze, and index a vast amount of web content.