Fitting It All Together
Let's take a look at a rough timeline of events starting in 1969 when GML came into use at IBM (see Figure 2-3).
Figure 2-3. Timeline of major events in SQL and XML
Surprisingly, the historical roots of XML go back further than those of SQL. Not that much further, though, and remember that nonrelational databases were around long before 1969.
XML data maps best onto trees. SQL data maps best onto arrays. These approaches are two totally different ways of looking at the world.
Those of you familiar with high school physics will know that as light travels through space it can be thought of as both a wave and a stream of particles (photons). Both of these views make sense, both are internally consistent, and predictions based on both views yield reproducible results. The question of whether light “really is” a particle or “really is” a wave is irrelevant and meaningless. Both the wave and the particle view are simply frameworks that we apply to make sense of reality, and both can be useful in predicting and understanding the universe.
Likewise, both relational databases and more object-oriented views of data such as XML can be applied to make sense of and process the vast amounts of information around us. Both approaches are useful in the process of delivering information to a user.
And that's what it's all about, isn't it? You can build a sublimely engineered information processing and retrieval system, but at the end of the day, it's the user's needs that have to drive the design of an application. The user always comes first, which is why, as we'll see in Chapter 3, gathering requirements is so important.
A Note on Standards
Understanding the world of international standards and standards bodies, especially in the IT family of industries, is a daunting task. In this journey of discovery, it pays to remember that the existence of international standards is responsible for the emergence of the industrial and information ages. Your Scandinavian mobile phone works in Hong Kong. You can ship a package from Barcelona to Fiji. You can access Web pages for AOL, Microsoft, Sun, and Sony. Systems built on top of international standards power this planet. Going back to our first example of XML in Chapter 1, we used an ISBN (International Standardized Book Number) to identify Homer's Odyssey uniquely. The ISBN is based on a standard from the ISO (the International Organization for Standardization). ISO is the granddaddy of standards organizations, but many other standards bodies and organizations exist to develop, publish, and/or promote international standards. SQL is an ISO standard, but most Web standards aren't from ISO because of the length of time it takes to develop an ISO standard. The W3C (World Wide Web Consortium—http://www.w3.org) is the home of most Web standards. Many people don't understand the relevancy of this powerful body. The W3C is a “member organization”; that is, the people who participate in the W3C standards efforts are representatives of member organizations and corporations, the same bodies that implement and use these standards. Two kinds of standards exist in the real world. De jure[3] standards (“from law”) are documents created and approved by formal standards bodies (for example, SGML, XML, and HTML). De facto standards (“from fact”) are no more than standards that come into being through common usage: They are standards because so many people use them (for example, the GIF image format, the ZIP compression format, WAP, and Word's “DOC” file format). Some de facto standards (such as WAP) have strong lobby organizations that promote their use, but that doesn't make them any less “de facto.” Both types of standards are important, and it's essential to note that something can be a “standard” without having been ratified by the ISO. And de facto standards are often supported better. For instance, Macromedia's proprietary Flash product is pervasive on the Web, but Scalable Vector Graphics (SVG), which is supported by the W3C, is currently implemented only on the W3C's own test bed Amaya browser. |
[3] Not to be confused with “du jour” standard (standard of the day). It often feels as if you're dealing with a “du jour” standard when you're using Web standards of any kind. For instance, in putting together this book, I've had to contend with the rapidly evolving XML and SQL standards.