XML in a Nutshell, 3rd Edition

How XML Works

Example 1-1 shows a simple XML document. This particular XML document might be seen in an inventory-control system or a stock database. It marks up the data with tags and attributes describing the color, size, bar-code number, manufacturer, name of the product, and so on.

Example 1-1. An XML document

<?xml version="1.0"?>
<product barcode="2394287410">
  <manufacturer>Verbatim</manufacturer>
  <name>DataLife MF 2HD</name>
  <quantity>10</quantity>
  <size>3.5"</size>
  <color>black</color>
  <description>floppy disks</description>
</product>

This document is text and can be stored in a text file. You can edit this file with any standard text editor such as BBEdit, jEdit, UltraEdit, Emacs, or vi. You do not need a special XML editor. Indeed, we find most general-purpose XML editors to be far more trouble than they’re worth and much harder to use than simply editing documents in a text editor.

Programs that actually try to understand the contents of the XML document—that is, do more than merely treat it as any other text file—will use an XML parser to read the document. The parser is responsible for dividing the document into individual elements, attributes, and other pieces. It passes the contents of the XML document to an application piece by piece. If at any point the parser detects a violation of the well-formedness rules of XML, then it reports the error to the application and stops parsing. In some cases, the parser may read further in the document, past the original error, ...