Internet

What Is HTML Parsing?

While sourcing for data, the way a web page is structured can determine how quickly the data can be collected. For instance, web pages with complex structures are harder and trickier to scrape, while those built-in simple and basic structures are easier to scrape.

Most web developers now use HTML to build, organize, and format their web pages and store content in them. This is convenient because it makes work easier for the developers and users who scrape from those sites.

However, not all websites are built this way, and this can make web scraping easily frustrating. Yet, for those who want to scrape HTML documents, below is a breakdown of other major uses of HTML and how to parse data scraped from HTML websites.

HTML and Its Usage on the Internet

HTML means HyperText Markup Language and can be explained as an easy language used to determine how elements are displayed on web pages.

However, it has other uses, including the following:

Web Pages Development

A principal application of HTML is in the building of web pages. This language has served as the official standard language for displaying web pages since 1999.

Developing with HTML is simple and easy.

Internet Navigation

While HTML is a general tool for building most of the pages on the internet, it is also the tool by which users can effortlessly navigate the internet.

One of the HTML elements known as anchor tags allows you to effortlessly go from one web page to the next as long as there are URLs on each subsequent page.

Offline Web Applications and Game Development

HTML is also used to help websites store cookies to easily retrieve basic information like usernames and authentication tokens to access web applications.

Similarly, HTML, especially the modern version 5, can develop 2D and 3D games that run on most browsers.

The process may not be entirely done with HTML, but one of its elements, canvas, is used to set the foundation before CSS or JavaScript is used to complete it.

Embedding Videos and Images

HTML also has elements that allow you to embed images and adjust their position, height, and weight to fit the desired ratio. You can also use the same element to set how the images should be rendered upon request.

Similarly, you can also use other elements to embed videos and adjust the controls, autoplay, thumbnails, and timestamp.

Data Storage

This language has also changed the way data is stored in browsers. For instance, it is now possible to collect and store user data on their browser using HTML. However, this depends on the permission settings of the user.

What is Parsing?

In the simplest term, parsing can be defined as the process of splitting a file into several parts, describing the syntactic roles of each part, and then moving to see if the syntaxes match the established HTML syntaxes.

If the entire syntaxes match the defined HTML syntaxes by the end of the process, the file is regarded as an HTML document. And if not, a parse error is raised and recorded.

A typical parser uses a process consisting of several code points, which are first passed through a tokenization stage before a tree construction stage. A file that successfully passes these stages can then be appended as an HTML document.

The Basic of HTML Parsing

HTML parsing combines tokenization and tree construction stages to determine if a file is an HTML document or not.

Below is a description of each layer to illustrate the basics:

1. The Input

The input of every HTML parsing is always a stream of code points that the average internet user often sees as a byte stream emanating from a local file system or network.

Then the byte stream is further converted into characters that can be easily decoded.

2. Stream Preprocessor

Once the input byte streams have been converted, the next stage begins with the characters serving as the new inputs.

The characters are usually arranged so that the current input character is the last character that has just been consumed while the next character is the first input yet to be consumed.

3. Tokenization Stage

This step involves using State Machines which are special HTML attributes that pick up character inputs to consume them. Some State Machines pick up singular characters while others pick up more than one input character at a time.

Due to these variations, the outputs that emerge from this stage can also vary. For instance, the output can be a series of zero, a character, a comment, DOCTYPE, start tag, end tag, or end-of-file.

The emitted output can then move into the final stage.

4. Tree Construction Stage

The outputs from the previous stage then go through this final lap to see if they qualify as documents or not.

HTML parsing can be combined with the powerful Python library, lxml, to make the task easier and faster. Taking an lxml tutorial should provide you with the basics to run this tool. This lxml tutorial demonstrates how to utilize Python for web scraping.

Conclusion

Parsing is a crucial part of web scraping. To collect unstructured data and turn it into structured data, you will need to parse it first.

HTML parsing is important because most web pages are now developed using HTML. Parsing with the markup language is hence a necessity. And luckily, the process is simple.

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