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Chapter 1. Introduction

What is XML and why should I care?

In a sentence, the eXtensible Markup Language (XML) is an open standard providing the means to share data and information between computers and computer programs as unambiguously as possible. Once transmitted, it is up to the receiving computer program to interpret the data for some useful purpose thus turning the data into information. Sometimes the data will be rendered as HTML. Other times it might be used to update and/or query a database. Originally intended as a means for Web publishing, the ad- vantages of XML have proven useful for things never intended to be rendered as Web pages.

Think of XML as if it represented tab-delimited text files on steroids. Tab-delimited text files are very human readable. They are easy to import into word processors, databases, and spreadsheet applications. Once imported, their simple structure make their content relative easy to manipulate. Tab-delimited text files are even cross-platform and operating system independent (as long as you can get around the car- riage-return/linefeed differences between Windows, Macintosh, and Unix computers). See the following example

Amanda

10

dog

brown

Blake

12

dog

blue

Jack

3

cat

black

Loosey

1

cat

brown

Stop

5

pig

brown

Tilly

14

cat

silver

The problem with tab-delimited text files are two-fold. First, the meaning of each tab-delimited values are not explicitly articulated. In order to know what each value is suppose to represent it is necessary to be given (or be told ahead of time) some sort of map or context for the data. Second and more import- antly, tab-delimited text files can only represent a very simple data structure, a data structure analogous to a simple matrix of rows and columns. Put another way, tab-delimited text files are exactly like flat file databases. There is no easy, standardized way of representing data in a hierarchial fashion.

Much like tab-delimited text files, XML files are very human readable since they are allowed to contain only Unicode characters -- a considerably extended version of the original ASCII character code set. Ad-

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