A brief introduction to xml

Table of contents

• Preface
  • General
  • Viewing tip
    • Figures
  • Supplemental material
• A brief introduction to XML
• Miscellaneous

Preface

General

This module is part of a collection dedicated to learning XML.

Viewing tip

I recommend that you open another copy of this document in a separate browser window and use the following links to easily find and view the figures while youare reading about them.

Figures

• Figure 1 . The structure of a simple book.
• Figure 2 . Very simple XML syntax.
• Figure 3 . XML syntax with attributes.

Supplemental material

I recommend that you also study the other lessons in my extensive collection of online programmingtutorials. You will find a consolidated index at www.DickBaldwin.com .

A brief introduction to XML

The name XML derives from e X tensible M arkup L anguage. According to Wikipedia,

"A markup language is a system for annotating text in a way which is syntactically distinguishable from that text."

In other words, when text has been annotated or marked up, the annotations can be easily distinguished from the original text. For example, if you turn in a termpaper and the professor annotates it with a red pencil, you can easily distinguish her annotations from your original text. However, XML doesn't usecolor to annotate text. Instead, XML uses specially formatted text to annotate text.

Structured documents

XML gives us a way to create and maintain structured documents in plain text that can be rendered in a variety of different ways. For example, before Iupload this document to the Connexions website for publishing, I will convert into CNXML , which is one of the many flavors of XML. Once the document is on the website inthat format, programs on the website have the ability to render it in the form of a web page (which you are probably reading right now) or in the form of a PDF document, which you can download andprint if you choose to do so.

There is a lot of jargon involved in XML. One of my objectives will be to explain the jargon.

What do I mean by a "structured document?"

I will answer this question by providing an example. A book is a structured document. In its simplest form, a book may be composed of chapters. The chaptersmay be composed of sections. The sections may contain illustrations and tables. The tables are composed of rows and columns. Thus, it would be possible to drawa picture that illustrates the structure of a book.

What do I mean by "plain text?"

Characters such as the letters of the alphabet and punctuation marks are represented in the computer by numeric values, similar to a simple substitutioncode that a child might devise. For example in one popular encoding scheme (ASCII), the upper-case version of the character "A" is represented by the value65, a "B" is represented by the value 66, a "C" is represented by 67, etc.

Different encoding schemes

The actual correspondence between the characters and the specific numeric values representing the characters has been described by several differentencoding schemes over the years. One of the most common and enduring schemes is a scheme that was devised a number of years ago by an organization known as theAmerican Standards Committee on Information Interchange. This encoding scheme is commonly known as the ASCII code.