Webクローラー

Webクローラーとは？

A data crawler, sometimes called a spider, is an Internet bot that systematically browses the World Wide Web, typically for the purpose of creating entries for a search engine index. Companies like Google or Facebook use web crawling to collect the data.

How Does a Data Crawler work?

A crawler starts with a list of URLs to visit, and it will follow every hyperlink it can find on each page and add them to the list of URLs to visit. Web Data Crawlers are mainly used to create a copy of all the visited pages for later processing by a search engine, which will index the downloaded pages to provide fast searches.

So there are basically three steps that are involved in the web crawling procedure. Firstly, the spider starts by crawling certain pages of a site. Next it keeps indexing the words and content of the site, and lastly it visits all the hyperlinks that are found in the site.

Date Crawler or Data Scraper?

We can say a crawler collects data thoroughly as everything on the web will eventually be found and spidered if it keeps visiting pages; however, it is also really time-consuming as it needs to go through all the links and it will drive you crazy when you have to recrawl every page to get new information.

When it comes to crawling, what springs to mind is getting all kinds of data from web. But true crawling actually refers to a very specific method of getting URLs, especially useful for indexing or SEO. It collects all the URLs, even those that contain data you do not need.

That is why we need another tool, data scraper, which is highly targeted and super fast. You can build a web scraper to a specific website and then scrape certain kind of data on that page. It is like a crawler guided by certain logic to just scrape data (not just URLs but any kind of data such as title) from pages you want, making the whole extraction process much more efficient.

What Can a Data Scraper Do?

Scrape a single page

Scrape multiple pages

Scrape detail pages

Any other pages