XML - 2

(XML Tree)

Example:

The image above represents one book in the XML below:

Giada De Laurentiis 2005 30.00 J K. Rowling 2005 29.99 Erik T. Ray 2003 39.95

The root element in the example is . All elements in the document are contained within .

The element has 4 children: <>, , .

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XML Tags are Case Sensitive

• Entity References

Some characters have a special meaning in XML.

If you place a character like "<" inside an XML element, it will generate an error because the parser interprets it as the start of a new element.

This will generate an XML error:

if salary <>

To avoid this error, replace the "<" character with an entity reference:

if salary < 1000 then

There are 5 predefined entity references in XML:

<	<	less than
>	>	greater than
&	&	ampersand
'	'	apostrophe
"	"	quotation mark

Note: Only the characters "<" and "&" are strictly illegal in XML. The greater than character is legal, but it is a good habit to replace it.

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XML Naming Rules

XML elements must follow these naming rules:

• Names can contain letters, numbers, and other characters
• Names cannot start with a number or punctuation character
• Names cannot start with the letters xml (or XML, or Xml, etc)
• Names cannot contain spaces

Any name can be used, no words are reserved.

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XML Elements are Extensible

XML elements can be extended to carry more information.

Look at the following XML example:

Tove Jani Don't forget me this weekend!

Let's imagine that we created an application that extracted the , , and elements from the XML document to produce this output:

MESSAGE To: Tove From: Jani Don't forget me this weekend!

Imagine that the author of the XML document added some extra information to it:

2008-01-10 Tove Jani Reminder Don't forget me this weekend!

Should the application break or crash?

No. The application should still be able to find the , , and elements in the XML document and produce the same output.