What Is XML?

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Java APIs for XML Kick Start
By Aoyon Chowdhury, Parag Choudhary

Table of Contents
Appendix B.  XML: A Quick Tour


XML stands for Extensible Markup Language. It is a meta language that can be used to define other languages. What that means is that XML does not have a predefined tag set or a grammar per se, thus making it fully extensible. It is merely a framework that provides the capability to create your own set of tags and the corresponding grammar. Therefore, when developing a language in XML, you can decide to create tags such as <carparts> or <engine>. The benefit you get in doing so is that you can make the tags content-oriented, in the sense that you can actually name the tags to represent the content that they store. Additionally, you can decide to create your own set of attributes for the tags to further qualify the contents. For example, you can create an attribute called capacity for the engine tag. Of course, because XML is extensible, you can also create tags that are purely for presentation purposes. The application that reads the XML document will need to determine what to do with the content stored in the tags.

At this point, you might wonder why we need XML. After all, there are several other markup languages available, such as SGML and HTML, so why not use them? XML was developed because the other markup languages were either not geared to handle content, or were too complex to be deployed over the Web. For example, SGML, the original meta language specification, is far too complex to be used meaningfully over the Web. HTML, another markup language, is more presentation-oriented than data-oriented. For example, the tag <HR> causes the browser to draw a horizontal line. Also, HTML is not extensible as it defines and understands a fixed set of tags and corresponding attributes, such as <H1>, <TABLE width='20'>, and so on.

So, the XML specification was developed to provide a mechanism with which developers could create their own language and grammar, and that was light enough to be deployed over the Web.


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JavaT APIs for XML Kick Start
JAX: Java APIs for XML Kick Start
ISBN: 0672324342
EAN: 2147483647
Year: 2002
Pages: 133

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