The internet is here to stay. From a small experiment carried out by a bunch of nuclear scientists to being omnipotent, the usage of internet has grown by leaps and bounds. Indeed, it is difficult today to envisage a world sans the World Wide Web. HTML stands for Hyper Text Markup Language and is the most commonly used simple tagging language for displaying text in a browser; however there is a limitation to what it can do. HTML focuses on the appearance of data by enhancing the appearance of text. It however, does not provide specifications to define new elements; you have to make do with pre-defined tags. In that sense, HTML is static.

XML stands for eXtensible Markup Language, which is a language that can be used to describe data in a meaningful way.  XML was developed to address the limitations of HTML. In particular, XML has provisions to define new elements and is considered dynamic because it is used to define a set of rules for encoding documents. The rules are defined in machine-readable and human-readable formats alike. The XML standards are set by W3 School

Virtually anywhere there is a need to store data; especially where it may need to be consumed by more than one application, XML is a good place to start. It has gained a reputation for being a candidate where interoperability is important, either between two applications in different businesses or simply those within a company. Hundreds of standardized XML formats now exist, known as schemas, which have been agreed on by businesses to represent different types of data, from medical records to financial transactions to GPS coordinates representing a journey. Incidentally, a ‘schema’ basically means a meaningful way of representing information. Or to put it differently, a schema is less formal and clearer way of representing information.

Why is XML used?

As discussed earlier, XML defines set of rules for encoding documents in a very easy to read format. Because XML has accepted standards, it can be parsed and interpreted by all types of programming languages and applications without errors or misconfigurations – by both machines as well by humans. It works behind the scenes to simplify the creation of HTML of large websites. XML facilitates exchange of information between systems and organizations. Data transfer is one of the most important aspects of any web application. This usually occurs over the Internet using an API (Application Programming Interface). XML is one of the important formats backend programmers use to create such APIs. XML is also used to modify the appearance and utility of various documents that are available on the Internet, as well as for creating creative layouts. XML is also useful for search engines as they can use XML tags to ascertain if the information on the webpage is relevant for the search phrase. This saves them time parsing the content of the entire page.
XML specifies neither semantics nor a tag set. In fact XML is really a meta-language for describing markup languages. In other words, XML provides a facility to define tags and the structural relationships between them. Since there’s no predefined tag set, there can’t be any preconceived semantics. All of the semantics of an XML document will either be defined by the applications that process them or by stylesheets.
There are provisions in XML for defining new elements while HTML doesn’t provide a specification to define new element and it uses predefined tags. XML can be used to build markup languages while HTML itself is a markup language.

Since XML does not have a fixed set of elements, the name of the linking element cannot be used to locate links. Instead, XML processors identify links by recognizing the xml:link attribute. Other attributes can be used to provide additional information to the XML processor. An attribute renaming facility exists to work around name collisions in existing applications.

Should you Learn XML?
By Internet standards, XML is pretty old. The first version of XML was introduced in 1996, and the markup language has been refined since then. As the name implies, the XML extends the capabilities of HTML. While HTML coders need to work with a set of predefined tags, XML coders can create their own tags, making XML more versatile and utilitarian.

Using XML means you no longer require writing focus programs on proprietary data software. Below are a few areas where XML is used.

XML is used in e-commerce applications, where it increases the accessibility of electronic data interchange for business transactions that involve clients and consumers. Another area where XML is used is wireless technologies. While mobile phones of today are quite powerful in terms of processing power, RAM and storage, the phones of yesteryear were extremely primitive. There was no way HTML could be used for these mobile phones. They needed a lightweight markup language that could  be used within a small device with limited computational resources, such as a mobile phone to access resources made available through the Wireless Application Protocol (WAP). WML is an XML-based markup language designed especially for mobile devices.

JSON (JavaScript Object Notation), the new kid on the block, has given XML a tough competition. However, the comparison between JSON (which we will cover in another article), is unfair as it is a data format while XML is a markup language. Both of them have their advantages and disadvantages. Most of the legacy websites are developed using XML, and there is no dearth of jobs for proficient XML developers. XML is still the preferred choice for specialized document formats (e.g., Word, Excel, etc.), transferring highly specialized and complex data (like financial data, for example), and for data exchanges between legacy systems that use XML.