XML Q & A

The XML Q&A......

1. What is XML for and how is it related to SGML?

XML is intended ‘to make it easy and straightforward to use SGML on the Web: easy to define document types, easy to author and manage SGML-defined documents, and easy to transmit and share them across the Web.’

It defines ‘an extremely simple dialect of SGML which is completely described in the XML Specification. The goal is to enable generic SGML to be served, received, and processed on the Web in the way that is now possible with HTML.’

‘For this reason, XML has been designed for ease of implementation, and for interoperability with both SGML and HTML.’

2.What is SGML and where is it used?

SGML is the Standard Generalized Markup Language, the international standard for defining descriptions of the structure of different types of electronic document.

SGML is very large, powerful, and complex.It has been in heavy industrial and commercial use for nearly two decades, and there is a significant body of expertise and software to go with it.

XML is a lightweight cut-down version of SGML, which keeps enough of its functionality to make it useful but removes all the optional features which made SGML too complex to program for in a Web environment.

3.Aren’t XML, SGML and HTML all the same?

Not quite! XML is an abbreviated version of SGML, to make it easier for you to define your own document types, and to make it easier for programmers to write programs to handle them. It omits all the options, and most of the more complex and less-used parts of

SGML in return for the benefits of being easier to write applications for, easier to understand, and more suited to delivery and interoperability over the Web.

HTML is just one of many SGML or XML applications, the one most frequently used on the Web

4. So why do we not just enhance HTML?

HTML was already overburdened with dozens of interesting but incompatible inventions from different manufacturers, because it provides only one way of describing your information.

XML allows groups of people or organizations to create their own customized markup applications for exchanging information in their domain (music, chemistry, electronics, hill-walking, finance, surfing etc).

HTML is now well beyond the limit of its usefulness as a way of describing information, and while it will continue to play an important role for the content it currently represents, many new applications require a more robust and flexible infrastructure.

5. So do we have to switch from SGML or HTML to XML?

No, existing SGML and HTML applications software will continue to work with existing files. But as with any enhanced facility, if you want to view or download and use XML files, you will need to use XML-aware software. There is much more being developed for XML than there ever was for SGML, so a lot of users are moving.