What Is a Data Crawler?
A data crawler,mostly called a web crawler, as well as a spider, is an Internet bot that systematically browses the World Wide Web, typically for creating a search engine indices. Companies like Google or Facebook use web crawling to collect the data all the time.
How Does a Data Crawler work?
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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 then index the downloaded pages so as to provide fast searches.
The web crawling procedure comprises of three steps. Firstly, the spider starts by crawling certain pages of a website. Next, it keeps indexing the words and content of the website, 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 the web. It collects all the URLs, even those that contain data you do not need. But true crawling actually refers to a very specific method of getting URLs, especially useful for indexing or SEO.
That is why we need another tool, data scraper (web scraper), which is highly targeted and super fast. You can build a web scraper to a specific website and then extract certain kind of data on that page. It is like a crawler guided by certain logic to extract data (not just URLs but any kind of data such as title) from the pages you want, making the whole extraction process much more efficient.
Why Data Crawler With Octoparse
Octoparse is a precise tool for the web scraping purpose. Not only does it save the amount of time for downloading the exact set of data that you want, but it also intelligently exports data into a structured format such as a spreadsheet or database.
Friday, January 22, 2021Web Scraping Challenges
Web scraping has become a hot topic among people with the rising demand for big data. More and more people hunger for extracting data from multiple websites to help with their business development. However, many challenges, such as blocking mechanisms, will rise when scaling up the web scraping processes, which can hinder people from getting data. Let’s look at the challenges in detail.
Web scraping may not work because:
1. Bot access
The first thing to check is that if your target website allows for scraping before you start it. If you find it disallows for scraping via its robots.txt, you can ask the web owner for scraping permission, explaining your scraping needs and purposes. If the owner still disagrees, it’s better to find an alternative site that has similar information.
2. Complicated and changeable web page structures
Most web pages are based on HTML (Hypertext Markup Language). Web page designers can have their own standards to design the pages, so web page structures are widely divergent. When you need to scrape multiple websites, you need to build one scraper for each website.
Moreover, websites periodically update their content to improve the user experience or add new features, which often leads to structural changes on the web page. Since web scrapers are set up according to a certain design of the page, they would not work for the updated page. Sometimes even a minor change in the target website requires you to adjust the scraper.
Octoparse uses customized workflow to simulate human behaviors so that to deal with different pages. You can modify the workflow easier to adapt to the new pages.
3. IP blocking
IP blocking is a common method to stop web scrapers from accessing data of a website. It typically happens when a website detects a high number of requests from the same IP address. The website would either totally ban the IP or restrict its access to break down the scraping process.
There are many IP proxy services like Luminati, that can be integrated with automated scrapers, saving people from such blocking. Angry birds for computer free download.
Octoparse Cloud extraction utilizes multiple IPs to scrape one website at the same time to not only make sure one IP would not request too many times but also keep the high speed.
4. CAPTCHA
CAPTCHA(Completely Automated Public Turing test to tell Computers and Humans Apart) is often used to separate humans from scraping tools by displaying images or logical problems that humans find easy to solve but scrapers don’t.
Many CAPTCHA solvers can be implemented into bots to ensure non-stopping scrapes. Although the technologies to overcome CAPTCHA can help acquire continuous data feeds, they could still slow down the scraping process a bit.
5. Honeypot traps
Honeypot is a trap the website owner puts on the page to catch scrapers. The traps can be links that are invisible to humans but visible to scrapers. Once a scraper falls into the trap, the website can use the information it receives(e.g. its IP address) to block that scraper.
Octoparse uses XPath to precisely locates items to click or to scrape, which largely reduces the chance of falling into the trap.
6. Slow/unstable load speed
Websites may respond slowly or even fail to load when receiving too many access requests. That is not a problem when humans browse the site as they just need to reload the web page and wait for the website to recover. But scraping may be broke up as the scraper does not know how to deal with such an emergency.
Octoparse allows users to set up auto-retry or retry loading when certain conditions are met to solve the issues. It can even execute customized workflow under preset situations. Download reimage repair.
7. Dynamic content
Many websites apply AJAX to update dynamic web content. Examples are lazy loading images, infinite scrolling and show more info by clicking a button via AJAX calls. It is convenient for users to view more data on such kind of websites but not for scrapers.
Octoparse can easily scrape those websites with different functions like scrolling down the page or AJAX Load.
8. Login requirement
Some protected information may require you to log in first. After you submit your login credentials, your browser automatically appends the cookie value to multiple requests you make the way most sites, so the website knows you’re the same person who just logged in earlier. So when scraping websites requiring a login, be sure that cookies have been sent with the requests.
What Is Web Scraping
Octoparse can simply help users to log in to a website and save the cookies just like a browser does.
9. Real-time data scraping
Web Scraping Using Octoparse
Real-time data scraping is essential when it comes to price comparison, inventory tracking, etc. The data can change at the blink of an eye and may lead to huge capital gains for a business. The scraper needs to monitor the websites all the time and scrape data. Even so, it still has some delay as the requesting and data delivery take time. Furthermore, acquiring a large amount of data in real-time is a big challenge, too.
Octoparse scheduled Cloud extraction can scrape websites at the minimum interval of 5 minutes to achieve nearly real-time scraping.
Web Scraping Tools
Jetpack joyride free play. There will certainly be more challenges in web scraping in the future but the universal principle for scraping is always the same: treat the websites nicely. Do not try to overload it. What’s more, you can always find a web scraping tool or service such as Octoparse to help you handle the scraping job.
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Artículo en español: 9 Desafíos de Web Scraping que Debes Conocer
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