Web crawlers: Back to the basics on how they work

A web crawler is a bot used to systematically search over millions of websites (mainly through its RSS feed) to get data from all over the web and store it.

The increasing value of the data has made these techniques of great interest to many companies given the ease to obtain the valuable information that later processed, may use for their purposes.

This means, that if you are using a specific search engine, the crawlers would go through each of the pages indexed in their database and get those pages to that particular server.

The web crawler follows all the hyperlinks in the websites and also search for other pages that are worth visiting, note changes to existing sites and mark dead links, all this to speed up the search.

It is necessary to take into account that scraping runs the risk of incurring in a violation of the intellectual property rights of the owners of the website.

Likewise, in some cases, can consist of the conduct of unfair competition when the purpose carried out by those third parties that apply the techniques of web scraping is susceptible of being an imitation.

Finally, this could lead to a possible violation of the legal terms and conditions of use established by the holders of the scraping website.

Starting from the above, we should be clear about some aspects that make up the general concept of a web crawler, such as, web search engines, web indexing (search engine index) and web scraping.

Web search engines

A web search engine is a software system that provides relevant and rich answers to the users through queries to search for specific information on the Web.

The search result it is generally presented in a line of results, the search engine result page (SERP). Search engines have three primary directives: Crawling, Indexing, and Ranking.

In simple word, It is a service that allows a user to access a particular type of information that is contained in an Internet server through search words entered by him, and displaying it in an orderly way.

The most popular search engine right now are Google, DuckDuckGo, and Bing. Why is this? Because most people want a single search engine that delivers three key features:

  1. Results you have actual interest.
  2. Simple interface (easy to read) and;
  3. Helpful options to broaden or tighten a search and these three search engines provide that.

Having that said, it is fair to ask, do we need multiple search engines? This depends on the needs of each one. In some cases, if the search is related to popular items, any search engine could do the work.

However, when the search is about a specific aspect, a scientific investigation or an aspect of research, it is always wise to use several search engines.

Since none of the popular ones are fail-safe and you would not want that small flaw in the search engine to become your flaw.

Web indexing (search engine index)

Search engine indexing is the process through which a search engine collects, parses and stores data for later use by the search engine.

The actual search engine index it´s like a little box (more like a directory list) to store the data collected by the search engines.

This index helps search engines to increase the speed of the searches.

Without an index, the search engine would take a lot of time and effort to iniate a search query.

It would have to search for every web page or piece of data that has to do with the particular keyword used in the search query as well as every other part of the information it has access to, to ensure that it is not missing something that has to do with the selected keyword.

Web scraping

Web scraping is a technique that allows you to extract hidden data in a document, such as web pages and PDF, in an automated way and makes it useful for later use. It refers to the cleaning and filtering of the data.

Its primary use is to get industrial quantities of information without typing a single word. Through the search algorithms, we can track hundreds of websites to extract only the information we need.

For this, we need to use a sequence of characters that form a search pattern, better known as “Regex” (regular expression), to delimit searches or make it more precise and to obtain better filtering of the information.

An effortless way to do this is with a formula in Google Spreadsheets.

You can find the primary applications of web scraping in content marketing, to gain visibility in social networks and,  control the image and visibility of a brand on the internet.

However, website crawlers are not regulation free, the Standard for Robot Exclusion or “SRE” commands the so-called “rules of politeness” for crawlers.

Because of this regulation, a web crawler must avoid source information from the files without authorization to be read. It must exclude it from its submission to the search engine index.

Also, crawlers in compliance of the Standard for Robot Exclusion or “SRE”  can´t bypass firewalls, to protect privacy rights.

Nevertheless, you may wonder if web crawlers are different from search engines?

The answer is straightforward:

Search engines are basically web crawlers able to arrange the collected websites and show the most relevant ones first.

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