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XML Concepts

XML is way of marking up data, adding metadata, and separating structure from formatting and style. Web pages are just one of many uses for XML.


sing XML for Web pages is just the tip of the XML story. With XML you can store information about your documents and pieces of your document. You can then use that information as criteria for displaying page—but also for validating digital signatures, sharing data across systems, processing data for other applications ... and much much more. Once you have an agreed-up method of storing metadata, the possibilities are almost endless.

With XML you create the tags you need for your documents.

XML stands for eXtensible Markup Lanugage. Each of these words describes an important part of what XML is and what it does.

The first word in XML is Extensible. This is the word that gives XML much of its strength and flexibility.

In HTML, there is a specified set of tags. You memorize these tags and use them. If you want to use any other tag, you are out of luck; what you see is what you can use. Period.

In XML, you create the tags you want to use. XML extends your ability to describe a document, letting you define meaningful tags for your applications. For example, if you site contains many glossary terms, you can create a tag called <glossary> for those terms. If it contains part numbers, you could use a <pn> tag. You can create as few or as many tags as your document needs.

This can be a little disconcerting at first because you can't go to a reference guide and look up the tags to use. But it also give you great freedom and flexibility because you can define and use tags in a way that makes sense for your documents.

Extensibility means you get more options and more power—but with those capabilities comes a need for planning. To make good use of XML, you'll want to know and understand your documents: what pieces comprise them, how those pieces relate to each other, and how to you want identify each pieces.

Remember, though, that you are extending your tags to identify elements by what they are—not by how they look. You are Nnot creating tags to identify elements as "10 point bold." You are creating tags to identify "chapter headings" or "book titles" or "players."

With XML you identify, or markup, elements within your document.

The second word in XML is Markup. This is the purpose of XML: to identify elements within your document.

Markup—be it XML, HTML, or your word processing program's own markup—is essential for documents to to make sense. Without markup, the computer sees your document as one long string of text, with each character having equal importance to every other character. Without markup, your document is just one bit clump of bits.

By marking up your document, you begin to give meaning to the pieces within. You identify the bits and pieces in a way that gives them value and context: "this is a paragraph," "this is a song title," ":this is a section head." And, with extensible markup you can mark up the document in ways that match your needs.

However, it is important to remember that markup is just a way of identifying information. This is an important and critical step—but by itself markup does nothing. Markup does not program the data to act in a certain way, to display in a certain way, or to do anything other than carry an identifying mark.

With XML you follow a set of rules and syntax to markup your document.

The third word in XML is Language. This states that XML follows a firm set of rules. It may let you create an extensible set of markup tags, but its structure and syntax remain firm and clearly defined.

In technology, the term "language" is often automatically appended to the word "programming" as in "programming language." Too often, people assume that all languages are for programming and for creating a set of actions. But a languages is just a way of describing something—be it a program's actions or a markup definition.

Extensible Markup Language is a means of marking up data, using a specific syntax.

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