Crawling vs Parsing

One of our favorite quotes goes: "If a problem changes by an order of magnitude, it becomes a different problem," and in that lies the answer to the question - Crawling or Parsing?

Crawling means working with large data sets, where you develop your crawler scripts (or bots) that penetrate into the deepest parts of web pages. Parsing, on the other hand, refers to the extraction of information from any source (not necessarily from the Internet).

Most often, regardless of the approaches used, we call website parsing data collection, and that is a serious misconception.

Crawling and Data Collection - Main Differences

1. Data collection does not necessarily require the Internet. Tools that help in data collection can relate to extracting information from a local machine or database. Even if the information is taken from the Internet, a simple "Save As" link on a page is also a subset of the data collection universe.

Data crawling, on the other hand, differs greatly in both scale and scope. First, crawling = web crawling, meaning that on the Internet we can only "crawl" data. Programs that perform this incredible task are called crawl agents, or bots, or spiders.

Some web spiders are algorithmically designed to reach the maximum depth of a page and crawl them iteratively (have we ever said "crawl"?). Although both methods seem different, parsing and crawling are basically the same thing.

2. The Internet is an open world and the quintessence of our right to freedom. Thus, a lot of content is created and then duplicated. For example, the same blog may be hosted on different pages, and our spiders do not understand that.

Therefore, data deduplication is an integral part of the web data crawling service. This is done to achieve two goals - to keep our customers satisfied by not flooding their databases with the same data multiple times, and to save space on our servers. However, deduplication is not necessarily a part of web data collection.

3. One of the most difficult tasks in parsing is coordinating sequential crawling. Our spiders must be polite to servers so as not to anger them during collection. This creates an interesting situation. Over time, our spiders must become smarter, learning from the data about collection errors.

They must learn to determine when and how hard to hit a server, and how to view data on its web pages while adhering to politeness policies. Although both options seem different, parsing and crawling are basically the same thing.

4. Finally, different crawling agents are used to crawl different websites, and therefore you need to ensure they do not conflict with each other in the process. Such a situation never arises when you are just going to view data.

In conclusion, speaking about parsing and crawling. Parsing is a very superficial aspect of crawling, which we call extraction, and for that again several algorithms and some automation are required.