what is xml?

by l. c. rees

start

We're ever deeply ensnared in a world wide web. Forests of techspeak, "information superhighway", "global village", "Infobahn", litter conversation. Offline, you're off-life, standing still as the information age hurls past. The moral of the age is "Go online, there's gold in those nets. Never know what you might catch".

This prodding rain of hype has been good incentive. From a few academics and hardcore hobbyists, Internet growth has gone nuclear. 300 million have been online, 55 million regularly. Blame for this falls on HTML, the HyperText Markup Language. HTML spins data into a World Wide Web, touching anyone, anywhere, anytime. The global reach of mass media is now in the hands of everyone.

As both sense experience and path for creation, HTML has advanced far beyond its first humble steps. But its virtues now shackle it. It can no longer move forward. But the makers of HTML have brought relief: XML.

What is XML? To answer, we must know:

• Why HTML worked.
• Why HTML no longer works.
• Why XML will pick where HTML left off.

why html worked

HTML outlines hypertext structure. Ideally, hypertext is data following a path imposed by user whim, linked and experienced independent of where it and its user are. Though the Web hasn't reached this ideal and perhaps never will, HTML's design grasps for it, emphasizing three concerns in data delivery:

• Linking: Data is linked in HTML, letting one piece carry you to another.
• Simplicity: HTML is simple, making it easy to learn
• Portability: HTML is stripped down, making it portable, especially over networks.

Each of these, when hard-wired into data by commands called markup, make hypertext. Markup says this is a paragraph <P>, this is a picture <IMG SRC="picture.gif">, and this is a link<A HREF="link.html">Link </A>. Say there's a line like:

Dick likes Jane. Run, Jane, run.

Straight English. Add markup:

<A HREF="dick.html">Dick</A> likes <A HREF="jane.html"> Jane. </A> <A HREF="run_jane.html" > Run, Jane, run.</A>

You get:

Dick likes Jane. Run, Jane, run.

Hypertext.

Anyone caring about Dick and Jane can then follow a link to more on Dick, Jane, or where Jane might run, instead of living in suspense.

HTML was the first way so much data could reach so many so easily. Radio and TV unleashed a lot of data but the flood was indiscriminate. Computers allowed higher interaction with thought but were limited by place and multi-platform babble. Only HTML allowed data to transcend the tyranny of place and distance.

But cracks begin to show.

why html no longer works

HTML markup is fixed. Linkage, simplicity, and portability demand limits on markup. That's fine, if you just want linkage, simplicity, and portability. If you Want more, you have a problem. HTML is limited in:

• Intelligence: How well data knows itself.
• Adaptation: How well data changes in response to changing times.
• Maintenance: How easily data is cared for.

Some intelligence infests HTML. It knows this is a paragraph and this is a picture. But it doesn't know the paragraph's about Dick and Jane and the picture is Brown Puppy's. It focuses on basics, not specifics. Dick and Jane can't be torn from Brown Puppy if Brown Puppy's all you want. You get everything in one swallow.

Power over intelligence lost.

You want more than HTML's limited markup. You want <DONUT> markup. You want <FILLED>, <SPRINKLES>, <FROSTED>, and <GLAZED> tags. But HTML won't give them to you. You could submit <DONUT> markup for exhaustive standards approval. Maybe you'll get it. If not, you're out of luck.

Power over adaptation lost.

HTML throws everything in one hat, one size fits all. Its hard to find and change the exact markup you want. Markup for look and linking get mixed in with data, with no clear division. Change look, links may be lost. Change links, look may be lost. Separate markup for links, look, and data don't exist. To change something you change everything.

Power over maintenance lost.

Is there a solution?

Yes. XML.

why xml will pick up where html left off.

Extensible Markup Language allows specific markup to be created for specific data. It has the virtues of HTML without any of its limitations. XML is strong in:

• Intelligence.
• Adaptation.
• Maintenance.
• Linking.
• Simplicity.
• Portability.

XML is intelligent to any level of complexity. Markup can be wrapped within markup from general markup like <DOG>Lassie</DOG> to more specific markup like <DOG><COME_HOME><SCOTTISH>Lassie </SCOTTISH></COME_HOME></DOG>. Data can be so finely marked up that <SEEING_TWO>double</SEEING_TWO> and <MORE_LIQUOR>double</MORE_LIQUOR> are infinitely separate values. The information knows itself. No more unwanted thought.

XML is a mother tongue for other languages, so markup languages like DickML and JaneML become possible. Adaptation is infinite. Custom markup can be created for any need. If markup describing how pepperoni pizza is different from sausage pizza is needed, it can be made. If markup describing the varying degrees of lumpiness in gravy is needed, it can be made. No more fixed markup to limit the categorizing instincts of the masses.

XML is easy to maintain. It contains only data and markup. Look comes from a separate stylesheet and links are separate, not buried in the document. Each can be maintained separately. Easy access and easy change. No more wading through a markup mess.

XML has one way to link embracing all ways to link. Not only that, it links in ways HTML can't. HTML can do simple, one way links within or outside data. XML does that but can also link two or more points within or outside data. There are even super-links intertwining all data within itself. Any link between any data can be handled.

XML is simple. When looking at XML the average user may find that hard to believe. Compared to HTML it's not. But compared other languages that let you do what XML does, it's simplicity itself. Unneeded overhead has been torn out in favor of essentials. XML gets to the point.

XML carries well. It's reason for existence is Power + Portability. All a browser needs to view XML is the data itself and the stylesheet controlling its look. If stricter validation is needed, a description listing out its exact meaning can be used with only slightly more overhead.

The solution is here.

why xml will pick up where html left off

This is the vision of XML from the people putting it together:

1. XML shall be straightforwardly usable over the Internet. It's designed to use proven methods and require little retooling to make it a vital part of the Web. Adoption is intended to be as painless as possible.
2. XML shall support a wide variety of applications. HTML's reach is widespread. It's independent of hardware or software. People with different platforms can access the same HTML using hundreds of different programs. XML must support a similar or greater range of uses and programs to be successful.
3. It should be easy to write programs which process XML documents. If you don't build it, they won't come. Why some some computing platforms win and others don't is the amount of software written for them. The test of a computer's usefulness is how much you can do with it. This applies to XML too. If nothing uses it, it dies. Making it as painless as possible for programs to use it is in the best interests of those who want XML to fly.
4. XML documents should be human-legible and reasonably clear. You should be able to read over a raw XML document and understand it. It may even be easier to understand than normal English. "Jack and Jill went up the hill.", marked up as <NAME>Jack</NAME> and<NAME>Jill </NAME>went <DIRECTION>up </DIRECTION> the <GEOLOGIC_FORMATION>hill.</GEOLOGIC_FORMATION> may be even more self-explanatory than its unmarked form.
5. The XML design should be prepared quickly. The first XML specification is out.
6. The design of XML shall be formal and concise. Instead of often obscure markup like <P>, <VLINK=00ff>, or <TR>, XML is spelled out. <P> would be <PARAGRAPH>. <VLINK=00ff> would be <VISITEDLINK=00ff>. <TR> would be <TABLEROW>. This makes XML easier to understand and compose.
7. XML documents shall be easy to create. XML documents are easy. If you can type <, >, and /, and remember that for every opening <MARKUP> there needs to be a closing </MARKUP> you can write "well-formed" XML. Complex or "valid" XML is more difficult but not overwhelming.
8. Terseness in XML markup is of minimal importance. HTML has a lot of shortened markup. The meaning of <IMG SRC> may be recognizable but if it's spelled out as <IMAGE SOURCE> it's even clearer. XML seeks to make its markup clear, as opposed to short, across the board.

This is the vision of XML. XML won't just supplement the Web. It will be the Web. Visions often die when they try to be all things to all people. The vision of XML won't. Its job is allowing visions to be all things to all people.

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