Part I
SGML Development: Essential Ideas, Terms, and Technology

1  Background and Nature of SGML

2  SGML View of the World: Structure, Content, and Format

3  SGML Terminology

4  The Basic Procedure

5  Two Scenarios

Chapter 1
Background and Nature of SGML

SGML and markup languages can make your life easier. In this chapter, you learn:

•  Why markup languages are so popular

•  What SGML has to do with ISO and CALS

•  How SGML makes information transportable

•  How SGML protects your formatting and structure

•  How SGML is already gaining popularity on the Internet

•  What the future holds for SGML

Why Markup Languages Are So Popular

Markup languages, such as SGML and HTML, have changed the nature of information. Thanks to them, you can transport information across the planet and through all kinds of computer platforms and hosts. Your documents always retain their original structure and format.

Presenting information no longer requires a specific machine. It does not matter whether you are writing on a UNIX box, a Macintosh, an IBM mainframe, or a PC. Markup languages—SGML in particular—make your treatise infinitely transportable without changing its original appearance. You can write a zoological treatise, a movie review complete with video and sound clips, or a multimedia presentation, and transport it without losing its structure, content, or format.

SGML also makes your documents modular, interchangeable, and flexible. Hypertext takes advantage of this sort of flexible presentation of information. For example, if you click highlighted text in a help file on your PC, your computer display automatically jumps to information related to that text. For that event to happen, someone had to mark up or encode the related information. SGML provides the greatest flexibility possible for this sort of information interchangeability.

When you make documents into SGML documents, you insert tags around document structures, like titles and paragraphs, that an SGML processing system can recognize and reconstruct on demand. The tags provide a blueprint for an SGML processing system to build your document according to your original design, regardless of platform or processing environment.

Tags make your documents look somewhat unrecognizable when not seen through an SGML viewing tool, but tools for dealing with SGML documents are increasingly available.

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Note:  
Tools for making and viewing SGML documents are on the SGML CD-ROM included with this book. See Appendix A for information on installing the software.

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Because these tools are increasingly available, SGML has become even more popular. Some tools are in the public domain. The CD-ROM included with this book has parsers and editors, and even a copy of Electronic Book Technology’s DynaText viewing tool, which includes the 1994 CIA Factbook encoded with SGML tags so you can see firsthand how effective SGML is.

SGML and the ISO and CALS Standards for Data

Individuals are not the only ones who like SGML. In fact, for many years, businesses and government have found that SGML serves their needs for transporting information. The International Standards Organization (ISO), an organization based in Geneva that develops international standards, is responsible for specifying the international SGML standard that businesses have been using for years. The Continuous Acquisition and Lifecycle Support (CALS) standards of the U.S. Department of Defense have also specified that SGML be used.

How SGML Relates to ISO

The document you hear about repeatedly is ISO 8879, which is the SGML standard. It defines the rules that SGML must follow; it is the document that makes SGML a standard. ISO 8879 ensures that everyone follows the same rules when developing a scheme for document markup.

Figure 1.1 illustrates how various types of data and machines can transport documents easily because of these standards. Without these standards, confusion would rule. Companies who don’t follow a universal standard have difficulty sharing information because of technicalities like file format conflicts, document incompatibility, document handling inconsistencies, and non-standardized practices. There are so many competing electronic technologies, for example, that if there were no international standard, companies would be forced to choose compatible hardware and software as dictated by their customers. Their inconsistent practices would result in a data flow resembling the messy left side of figure 1.1. With an international standard, companies can choose their hardware and software based on their needs and simply run SGML compliant software to ensure standardized document interchange.

Fig. 1.1  Without international standards, companies cannot understand, let alone interpret, one another’s data.

In large-scale sharing of documents, even small inconsistencies can translate into enormous headaches. SGML unifies the different ways of handling data among defense contractors. It helps individuals share documents worldwide, too.

How SGML Relates to CALS

Standards must be very specific. Government contractors must define each type of data that they share. A disinterested third party, however, has to ensure that everyone uses the same definitions. The Defense Department started the CALS initiative to unify data and document exchange among defense contractors. Four standards are part of CALS, one of which is SGML. Table 1.1 summarizes the standards.

These standards make data flows more uniform and usable by multiple clients and authors. They replace paper flows with electronic documentation and provide for convenient access to information. It costs far less than a hard copy system without standards, and access is instantaneous.