XML Xplained

Introduction - Where are we now? How did we get here?

• Before the invention of writing, mankind was dependent on speech and wall painting for the communication of abstract ideas. These were effective instruments within small, close knit groups but were subject to ambiguity and loss of meaning when extended to wider groups and over even short spaces of time. Who really knows today what a cave painting meant to the painter?
• The invention of writing and in particular of the alphabet ushered in a new era in which thought, ideas and facts could be captured for the present and still remain meaningful in the future despite historical and cultural change. This, for many, is the true dawn of civilisation. Unfortunately the technology then available to support writing - pen and paper, wax and stencil, stone and chisel - was not capable of mass production and distribution so the information contained in the writing was only accessible to a small, select group of literate men - the clerks who wrote the ideas down and who became a sort of priesthood of knowledge.
• When, in about 1450, Gutenberg demonstrated his printing press using movable type, he launched a revolution that changed the face of the world. By doing so, he liberated information from the control of the few and gave access to the many. Gutenberg's small technical change had massive and unforeseen results. Before the invention of printing, the number of manuscript books in Europe could be counted in tens of thousands. By 1500, after only 50 years of printing, there were more than 9 million books. This had a profound effect on the development of major European languages, creating standards and giving rise to an entirely new industry: publishing.
• It also changed the way people thought. Readily available cheap books and newspapers made education and information accessible to a much wider part of society, producing a ferment of ideas leading to religious and political wars, revolutions and massive economic change.
• Now this process seems to be happening again. A series of technological changes is ushering in a new Digital Age which will have as profound an effect on the way we think, use information and do things as did Gutenberg's revolution.
• The digital revolution will, it is suggested, change the way information is used and appreciated. Print technology and the world based upon it offers access to information at a very high level, rather like dealing with chemistry purely at the level of complex compounds or crystals. The digital revolution allows us to go deeper and access the ?atoms? of information, to recombine and reuse them to produce new and novel constructs that will alter the way we think about the world around us.
• Like Gutenberg?s revolution, the Digital Age is based on the combination of a number of technological trends coming together into a single architecture. In Gutenberg?s case this was the printing press, moveable type and paper technologies. In today?s case it is a fully mature web, the key components of which are now clear:

* The existence of mark-up languages which allow the production of simple streams of self-descriptive data which can be understood on any and every platform;

* The hypertext idea, and its implementation on the world wide web, which allows the linking of information objects which have contextual or semantic relationships irrespective of format or location;

* Universal availability of cheap storage media, connectivity and PCs to process and render information;

* A network, the Internet, owned by no one and everyone, ubiquitous and self-repairing;

* Finally, the last piece, today?s movable type so to speak, XML, a set of standards which directly support the needs of those who would use the Web for cultural, scientific and business purposes.

• The purpose of this paper is to focus on XML, the eXtensible Markup Language, what it is, why it was invent