What is XML and Why use it .

Extensible Markup Language (XML) is a markup language that defines a set of rules for encoding documents in a format which is both human-readable and machine-readable. It is defined by the W3C's XML 1.0 Specification and by several other related specifications, all of which are free open standards.
The design goals of XML emphasize simplicity, generality and usability across the Internet. It is a textual data format with strong support via Unicode for different human languages. Although the design of XML focuses on documents, it is widely used for the representation of arbitrary data structures such as those used in web services.
Several schema systems exist to aid in the definition of XML-based languages, while many application programming interfaces (APIs) have been developed to aid the processing of XML data.
Five reasons you should use it in your designs.

Simplicity – XML is easy to understand. You create the tags and overall set up of your document. What could be simpler than that? When writing a page in XML, the element tags are your own creation. You are free to develop the system based on your needs 

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Organization – XML allows you to build your platform by segmenting the design process. Data sits on one page, and formatting rules stay on another. If you have a general idea of what information you need to produce, you can write the data page first then work on the design. XML allows you to produce the site in stages and stay organized in the process.

Accessibility – With XML you compartmentalize your work. Separating data makes it accessible when changes are needed. If you write both segments in HTML, you create sections that incorporate the formatting instructions with the information you need to display on the page. When time comes to change an inventory record or update your details, you must wade through all the code to find a few lines. With XML, separating data makes changes easy and time-saving.

Standardization – XML is an international standard. This means that anyone in the world is likely to have the ability to view your document. Whether you search for visitors in Alabama or Timbuktu, chances are they can to access the page. XML puts the world in your virtual backyard.

Multiple Applications – You can make one data page and use it over and over again. This means if you are cataloging inventory, you only do it once. You can create as many display pages as you want for that data. XML allows you to generate different styles and formats based on one page of information.