This is chapter one from the book, XML and FrameMaker, by Kay Ethier (Apress, ISBN: 159059276X. 2004). Ethier reviews some of the basic XML terms and rules, and provides a basic overview of the purpose of DTDs and XSLT.
This book is geared to XML users who wish to learn about publishing with Adobe FrameMaker. Because many FrameMaker users will also read this book to learn about publishing with XML, the book begins with an overview of XML. Learning XML is a good starting point for FrameMaker users, and may be skipped by those who are already XML savvy.
Understanding Markup Languages
XML stands for Extensible Markup Language, which is sometimes written as eXtensible Markup Language (either is appropriate). XML is named and defined by the World Wide Web Consortium (W3C). XML's specifications are set by the W3C and any revisions come through them.
A markup language is not a language in the way C++ and COBOL are languages. The markup is the key. It means that tags are put around your content-marking it with delimiters.
NOTE: W3C=World Wide Web Consortium, the governing body for web technologies. Further details may be found on the w3c.orgwebsite.
Reviewing the Evolution of XML
XML has its roots in another markup language-Standard Generalized Markup Language (SGML). SGML is a very complex markup language used by government and industry to share content in simple, ASCII-format files. Because files are a combination of tags (elements) and content, they can be understood fairly well when read from printouts. One advantage the government saw in this was that if a computer system was lost, the data in print could still be understood from its tags. SGML, however, turned out to be just the beginning.
Because of its complexity, a simpler markup language was thought to be needed-one that was both easier to use and optimized for the Internet. So, SGML was used to create Hypertext Markup Language, or HTML. Being a very small set of tags, HTML was more manageable and easier to learn and use. The results of HTML's rollout can be seen in the explosion of HTML content (the Web) during the 1990s.
HTML, however, had limitations. Because it was a specific list of tags, there was no good way to represent pieces of information. Something tagged with an HTML tag could be displayed as a heading, but could not be further delineated. Was it merely a heading above content, or was it a part within a catalog, or a document section, or a person's name? Companies were screaming for more and better markup options, with tags that they could use based on information types. Consequently, a scaled-down version of SGML was created that was called XML. XML overcame HTML's limitations, and has the functionality to let companies create tags as needed.
In the W3C's XML 1.0 Recommendation, the W3C describes its goals for XML. These design goals, as stated on the W3C website, are:
XML shall be straightforwardly usable over the Internet
XML shall support a wide variety of applications
XML shall be compatible with SGML
It shall be easy to write programs which process XML documents
The number of optional features in XML is to be kept to the absolute minimum-ideally zero
XML documents should be human-legible and reasonably clear
The XML design should be prepared quickly
The design of XML shall be formal and concise
XML documents shall be easy to create
Terseness in XML markup is of minimal importance
The bottom line is that XML was designed to fit where HTML was falling short in both extensibility and reusability. For some applications (uses), HTML just did not offer enough flexibility. Web designers and information managers (among others) wanted more from a markup language, but didn't want to work with SGML. The end result is that XML is a simpler, yet still powerful, alternative.
NOTE: XML is not the only technology overseen by the W3C. Many technologies exist that interact with XML and HTML. These include CSS and XSLT, which are discussed in Chapter 9.
This chapter is from XML and Framemaker, by Kay Ethier (Apress, 2004, ISBN: 159059276X). Check it out at your favorite bookstore today.