What is a Web Crawler: How Web Spiders Work? | Intellipaat

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What is a Web Crawler
Updated on 02nd Sep, 23 6.5 K Views

Additionally, web crawlers can also be used for other purposes, such as monitoring websites for updates, collecting data for market research, or building custom search engines for specific niches.

Here are the following topics we are going to cover in this blog:

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What is a Web Crawler?

An automated software called a web crawler, commonly referred to as a spider, systematically browses the World Wide Web in order to index websites for search engines.

Online crawlers’ main job is to gather information from websites, such as text, images, videos, and links, and store it in a database so that it may be processed and analyzed later.

The basic process of web crawling involves sending a request to a web server for a specific page, downloading the HTML content of the page, and then parsing that content to extract the relevant data.

The crawler then follows any links on the page, repeating the process of sending requests, downloading content, and parsing data until it has indexed all of the pages on the website.

Web crawlers play a crucial role in the functioning of search engines. Without web crawlers, search engines would be unable to efficiently index websites, and as a result, users would not be able to find the information they are looking for.

For example, when a user types a query into a search engine, the search engine uses its database of indexed web pages to generate a list of relevant results.

The results are ranked based on various factors, such as the relevance of the keywords in the query to the content on the web pages, the popularity of the pages, and the quality of the content.

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Importance of Web Crawler

Web crawlers are essential to the internet, as they help search engines index webpages so they can be found in search results. Crawlers also help with data collection, as they can traverse the web and gather data from many sources.

Additionally, they are used to monitor website changes and detect malicious activities, such as malware and phishing attempts. Finally, web crawlers can be used to discover new content or identify trends and patterns in large datasets.

Search engine crawlers are the most common type of web crawler, as they are used to discover new webpages, index them, and make them available in search results.

Crawlers use algorithms to determine which websites to crawl, how frequently to crawl them, and how many pages to index. This helps search engines provide the most accurate and relevant results to their users.

Data crawlers are used to gather data from multiple sources, such as web pages, databases, and APIs. This data can be used to generate insights and enable decision-making.

For example, a business might use data crawlers to monitor their competitors’ prices and adjust their own accordingly.

Web crawlers can also be used to detect malicious activities. For example, they can detect phishing attempts by looking for certain keywords or patterns. They can also detect malware by scanning websites for malicious code.

Finally, web crawlers can be used to discover new content and identify trends and patterns in large datasets. For example, they can be used to monitor social media feeds and identify emerging topics or popular trends.

Types of Web Crawlers

In the above section, we have seen the importance of web crawlers. Now it’s the right time to see the different types of Web Crawlers:

Types of Web Crawlers
  • Structured Data Crawler: A web crawler that is built to navigate webpages, extract structured data, and store it in a structured format is known as a structured data crawler.

This kind of crawler is frequently used to extract particular types of data, such as customer reviews, product details, or price information.

  • Recursive Web Crawler: Recursive web crawlers visit and revisit web pages, following each link until they have indexed the entire website. This kind of crawler is frequently used to index websites for SEO purposes.
  • Incremental Web Crawler: A web crawler that visits web pages progressively is known as an incremental web crawler. This indicates that only the pages that have changed since the crawler’s last visit to the website will be indexed.

This kind of crawler is frequently used to keep an eye out for updates and modifications to a website.

  • Deep Web Crawler: The deep web, which is the hidden content that is inaccessible through standard search engines, is a type of web crawler that is made to crawl it. This kind of crawler is frequently used to locate stuff that is otherwise hidden or difficult to access.

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Web Crawler Architecture

Web Crawler Architecture refers to the design and structure of a program that automatically browses the web for information. The architecture of a web crawler is responsible for defining how the crawler functions, what it does, and how it interacts with the websites it visits.

At a high level, a web crawler has three main components: the front end, the back end, and the storage system. The front end is the user interface where the user inputs the initial URL and specifies what information they want to extract.

The back end is responsible for performing the actual web crawling process and consists of multiple modules such as a URL scheduler, a downloader, and a parser.

The URL scheduler is responsible for keeping track of which URLs have been visited and deciding which URLs should be visited next.

The downloader retrieves the HTML content of the web pages and passes it to the parser. The parser then extracts the relevant information and stores it in the storage system.

The storage system is responsible for keeping track of the information that has been extracted by the parser and organizing it in a way that is easily accessible and searchable. This can be a database or a file system.

A well-designed web crawler architecture is crucial to the success of a web crawling project. It determines how the web crawler operates, what information it can extract, and how that information can be stored and retrieved.

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How does a Web Crawlers Work?

A web crawler is a program that searches the web and downloads content from websites. It works by starting with a list of URLs, then it visits each URL in the list and downloads the content on the web page.

It then follows any links on the web page and repeats the process to download the content of the linked pages as well. The web crawler can either index and store the content of the web page, or use the data to generate reports.

The web crawler usually uses a set of rules or algorithms to determine what content should be downloaded from the websites.

It can be programmed to recognize the content that is most relevant to a particular topic or search query. It can also be programmed to ignore certain types of content, like images, audio, and video files.

The web crawler tool can also be programmed to ignore any content that is too large or is not relevant to the search query.

It can also be programmed to pause between visits to a particular website to prevent the website from being overloaded with requests.

The web crawler is an important part of search engine technologies and can be used to create more accurate search results. It is also beneficial to website owners as it helps them keep their content up-to-date and relevant.

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Web Crawlers are essential for indexing and analyzing the vast amounts of information available on the web. They play a crucial role in search engines, content aggregators, and data mining, providing us with the information and resources we need to make informed decisions and access the information we need.

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