Web Scraping: Introduction, Applications and Best Practices

Web scraping typically extracts large amounts of data from websites for a variety of uses such as price monitoring, enriching machine learning models, financial data aggregation, monitoring consumer sentiment, news tracking, etc. Browsers show data from a website. However, manually copy data from multiple sources for retrieval in a central place can be very tedious and time-consuming. Web scraping tools essentially automate this manual process. 
This article intends to get you up to speed on the basics of web scraping. We’ll cover basic processes, best practices, dos and don’ts, and identify use cases where web scraping may be illegal and have adverse effects. 

Basics of Web Scraping

“Web scraping,” also called crawling or spidering, is the automated gathering of data from an online source usually from a website. While scraping is a great way to get massive amounts of data in relatively short timeframes, it does add stress to the server where the source is hosted. 
This is primarily why many websites disallow or ban scraping all together. However, as long as it does not disrupt the primary function of the online source, it is fairly acceptable. 
Despite its legal challenges, web scraping remains popular even in 2019. The prominence and need for analytics have risen multifold. This, in turn, means various learning models and analytics engine need more raw data. Web scraping remains a popular way to collect information. With the rise of programming languages such a Python, web scraping has made significant leaps.

Typical applications of web scraping

Social media sentiment analysis

The shelf life of social media posts is very little, however, when looked at collectively they show valuable trends. While most social media platforms have APIs that let 3rd party tools access their data, this may not always be sufficient. In such cases scraping these websites gives access to real-time information such as trending sentiments, phrases, topics, etc. 

eCommerce pricing

Many eCommerce sellers often have their products listed on multiple marketplaces. With scraping, they can monitor the pricing on multiple platforms and make a sale on the marketplace where the profit is higher. 

Investment opportunities

Real estate investors often want to know about promising neighborhoods they can invest in. While there are multiple ways to get this data, web scraping travel marketplaces and hospitality brokerage websites offer valuable information. This includes information such as the highest-rated areas, amenities that typical buyers look for, locations that may be upcoming as attractive renting options, etc.  

Machine learning

Machine learning models need raw data to evolve and improve. Web scraping tools can scrape a large number of data points, text and images in a relatively short time. Machine learning is fueling today’s technological marvels such as driverless cars, space flight, image and speech recognition. However, these models need data to improve their accuracy and reliability. 
A good web scraping project follows these practices. These ensure that you get the data you are looking for while being non-disruptive to the data sources. 

Identify the goal

Any web scraping project begins with a need. A goal detailing the expected outcomes is necessary and is the most basic need for a scraping task. The following set of questions need to be asked while identifying the need for a web scraping project:

• What kind of information do we expect to seek?
• What will be the outcome of this scraping activity?
• Where is this information typically published?
• Who are the end-users who will consume this data?
• Where will the extracted data be stored? For e.g. on Cloud or on-premise storage, on an external database, etc.
• How should this data be presented to its end-users? For e.g. as a CSV/Excel/JSON file or as an SQL database, etc.
• How often are the source websites refreshed with new data? In other words, what is the typical shelf-life of the data that is being collected and how often does it have to be refreshed?
• Post the scraping activity, what are the types of reports you would want to generate?

Tool analysis

Since web scraping is mostly automated, tool selection is very important. The following points need to be kept in mind when finalizing tool selection:

• Fitment with the needs of the project
• Supported operating systems and platforms
• Free/open-source or paid tool
• Support for scripting languages
• Support for built-in data storage
• Available selectors
• Availability of documentation

Designing the scraping schema

Let’s assume that our scraping job collects data from job sites about open positions listed by various organizations. The data source would also dictate the schema attributes. The schema for this job would look something like this:

• Job ID
• Title
• Job description
• URL used to apply for the position
• Job location
• Remuneration data if it is available
• Job type
• Experience level
• Any special skills listed

Test runs and larger jobs

This is a no-brainer and a test run will help you identify any roadblocks or potential issues before running a larger job. While there is no guarantee that there will be no surprises later on, results from the test run are a good indicator of what to expect going forward.

1. Parse the HTML
2. Retrieve the desired item as per your scraping schema
3. Identify URLs pointing to subsequent pages

Once we are happy with the test run, we can now generalize the scope and move ahead with a larger scrape. Here we need to understand how a human would retrieve data from each page. Using regular expressions we can accurately match and retrieve the correct data. Subsequently, we also need to catch the correct Xpaths and replace them with hardcoded values if necessary. You may also need support from an external library. 
Often you may need external libraries that act as inputs on the source. For e.g. you may need to enter the Country, State and Zipcode to identify the correct values that you need.
Here are a few additional points to check:

1. Command-line interface
2. Scheduling for the created scrape 
3. Third-party integration support (e.g. for Git, TFS, Bitbucket)
4. Scrape templates for similar websites

Output formats

Depending on the tool end-users can access the data from web scraping in several formats:

• CSV
• JSON
• XML
• Excel
• SQL Server database
• MySQL Database
• OleDB Database
• Script (A script provides data from almost any data source)

Improving the performance and reliability of your scrape

Tools and scripts often follow a few best practices while web scraping large amounts of data. 
In many cases, the scraping job may have to collect extremely large amounts of data. This may take too much time and encounter timeouts and endless loops. Hence tool identification and understanding its capabilities is very important. Here are a few best practices to help you better tune your scraping models for performance and reliability.

1. If possible, avoid the use of images while web scraping. If you absolutely need images, you must store these in a local drive and update the database with the appropriate path.
2. Certain Javascript features can cause instability. Certain dynamic features may cause memory leaks, website hangs or even crashes. It is absolutely important to remember that the normal activity of the information source must not be disrupted in any way. In such scenarios, a few tools use web crawler agents to facilitate the scrape. Very often, using a web crawler agent can be up to 100 times faster than using a web browser agent. 
3. Enable the following options in your scraping tool or script – ‘Ignore cache’, ‘Ignore certificate errors’, and ‘Ignore to run ActiveX and flash’.
4. Call a terminate process after every scrape session is complete
5. Avoid the use of multiple web browsers for each scrape 
6. Handle memory leaks

Things to stay away from

There are a few no-no’s when setting up and executing a web scraping project. 

1. Avoid sites with too many broken links
2. Stay away from sites that have too many missing values in their data fields
3. Sites that require a CAPTCHA authentication to show data
4. Some websites have an endless loop of pagination. Here the scraping tool would start from the beginning once the number of pages exhausts.
5. Web scraping iframe-based websites
6. Once a certain connection threshold reaches, some websites may prevent users from scraping it further. While you can use proxies and different user headers to complete the scraping, it is important to understand the reason why these measures are in place. If a website has taken steps to prevent web scraping, these should be respected and left alone. Forcibly web scraping such sites is illegal. 

Web scraping has been around since the early days of the internet. While it can provide you the data you need, certain care, caution and restraint should be exercised. A properly planned and executed web scraping project can yield valuable data – one that will be useful for the end-user. 

References

1. “Web Scraper Test Drive! – Web Scraping”, n.d. Accessed July 26, 2019. .
2. “Top 5 Web Scraping Tools Comparison | Octoparse”, n.d. Accessed July 26, 2019. https://www.octoparse.com/blog/top-5-web-scraping-tools-comparison.
3. “10 Best Web Scraping Tools to Extract Online Data – Hongkiat”, n.d. Accessed July 26, 2019. https://www.hongkiat.com/blog/web-scraping-tools/.
4. “Web Scraping Explained”, n.d. Accessed July 26, 2019. https://www.webharvy.com/articles/what-is-web-scraping.html.
5. “Web Scraping – Wikipedia”, n.d. Accessed July 26, 2019. https://en.wikipedia.org/wiki/Web_scraping.
6. “Big List of Web Scraping Uses: Application of Web Scraping to …”, n.d. Accessed July 26, 2019. http://www.entropywebscraping.com/2017/01/01/big-list-web-scraping-uses/.

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