XML stands for eXtensible Markup Language. XML is a meta-markup language developed by the World Wide Web Consortium(W3C) to deal with a number of the shortcomings of HTML. As more and more functionality was added to HTML to account for the diverse needs of users of the Web, the language began to grow increasingly complex and unwieldy. The need for a way to create domain-specific markup languages that did not contain all the cruft of HTML became increasingly necessary and XML was born.
The main difference between HTML and XML is that whereas in HTML the semantics and syntax of tags is fixed, in XML the author of the document is free to create tags whose syntax and semantics are specific to the target application. Also the semantics of a tag is not tied down but is instead dependent on the context of the application that processes the document. The other significant differences between HTML and XML is that the an XML document must be well-formed.
Although the original purpose of XML was as a way to mark up content, it became clear that XML also provided a way to describe structured data thus making it important as a data storage and interchange format. XML provides many advantages as a data format over others, including:
- Built in support for internationalization due to the fact that it utilizes unicode.
- Platform independence (for instance, no need to worry about endianess).
- Human readable format makes it easier for developers to locate and fix errors than with previous data storage formats.
- Extensibility in a manner that allows developers to add extra information to a format without breaking applications that where based on older versions of the format.
- Large number of off-the-shelf tools for processing XML documents already exist.
The world of traditional data storage and XML have never been closer together. To better understand how data storage and retrievel works in an XML world, this paper will first discuss the past, present, and future of structuring XML documents. Then we will delve into the languages that add the ability to query an XML document similar to a traditional data store. This will be followed by an exploration of how the most popular RDBMSs have recognized the importance of this new data storage format and have integrated XML into their latest releases. Finally the rise of new data storage and retrieval systems specifically designed for handling XML will be shown.
