scraping v.s crawling

When designing a web data collection enterprise, it is essential to understand the subtle differences in the various technical terms. The most common question is about the differences between web scraping and web crawling and which one would be the right fit for the job. 

These terms are indeed confusing as they are closely related, and under some circumstances, they even overlap. 

This article will uncover the complete process behind data collection and clarify the main differences between web scraping and web crawling and when you should apply each technique.

How does data collection work

When you design a system for aggregating publicly available information from the internet, it is crucial to understand the steps and decision points you are facing. 

Each domain/website has it’s own unique structure and page-to-page relations and links. It means you must understand how the website/data source you target is structured and plan your web scraping operation.

Usually, it is a multistep process. You would first need to fetch the data from the pages and then find out what pages are relevant for data extraction.

For this example, you’d need first to crawl the website and fetch the specific URLs holding the data as candidates for the scarping. A special scraper does this job; we will call a Web Crawler since it usually returns links and “crawls” through the pages instead of recovering data. Once we have the links, we can send a Web Scraper to those URLs and fetch the data points of interest.

So, What is Web Crawling?

Web crawling is the “getting the candidates” step in the process. It’s commonly known as a web crawler/spider because it works very much like a spider does, crawling over a virtual web made from web pages, one link to the next. 

The most prominent web crawler is Google’s spider, which crawls the entire internet, page by page daily. Crawling one website though, is the more common usage for most companies and developers. 

When designing a crawler for a specific website, you must know the type of links that are of our interest and, more importantly, keep track of the URLs that have been fetched and avoid re-crawling pages again. Most websites have circular links, which means that you may return to the original page if you follow a link after link. Tracking visited pages is therefore necessary here.

What is Web Scraping?

Web scraping is the actual act of extracting the data from a page. It usually involves analyzing the HTML of the desired page and setting the scraper to collect data from specific elements of the HTML tree. 

Its either done using an online web scraper or a raw HTML file and once you have the HTML of the page you desire to scrape, you can perform the scraping operation whenever you wish. 

Using this technique helps developers deal with the central issue of web scraping, which is that pages tend to change over time, and the scraper needs to be updated regularly. So fetching the HTML as a first step and then scraping the data off it can save the need of getting it twice, and only fixing the scraper.

What Are The Applications of Web Crawling?

Web crawling might be applied for several use cases; most of them involve understanding the structure of the website you are trying to scrape. The main issue with web crawling is that you usually don’t know how many pages will be there, before starting the crawling process.

The main applications in the eCommerce world are getting product links from a search page, crawling an eCommerce website to get all of the products in it, building a category tree from pages on an eCommerce store, and more.

What Are The Applications of Web Scraping:

Since scraping is getting the data off a page, most of the operations that come in mind when thinking of data fetching are scraping procedures. We need to understand that crawling involves scraping; also, it is just scraping the links.

When we get price or description data from a product page, reviews from a review section of a product, or SEO ranks on google, and we need to use a web scraper.

What is the relation between a Web Scraper and a Web Crawler?

This question will clarify the differences between the scraping and crawling because using them both in one operation might be complicated. 

When we only need data from a specific URL, a web scraper will be enough. But when we need first to fetch URLs to scrape and then get the data off them, we will combine a Web Crawler and a Web Scraper. The operation will start with a crawler, which creates the URL candidates to scrape and then a scraper that scrapes the data from those pages.

For example, if we want to search an eCommerce website for a specific term and then get all of the product titles and prices. For this kind of operation, we will combine a crawler and a scraper:

Step 1: Crawl the search URL, fetching all of the URLs for the products.

Step 2: Scrape each of the URLs of the list from step 1, and return the title and price of the product.

Using an API for crawling and scraping

Scrapezone allows you to use a simple and already built API for crawling, scraping, or a combination of your choice. Using our API will save you the time and money needed for creating crawlers and scrapers. Our experienced team will assist you in implementing your requirements into simple, fast, and scalable APIs.

Conclusion

Although the distinction between the two is very subtle, it is vital to understand it. When designing your data fetching operations, knowing how many steps of crawling and scraping is the most important when coding your software solution. I hope the distinction is clear now, and when designing your system, you will be able to plan it properly.

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