XML

Introduction to XML (Extensible Markup Language)

• was design to describe data and focus what data is.

was created to structure, store, and transport information.

• with XML, we can invent our own tag, an example like <to> and <from> which are not defined in any XML standard.
• XML is not a complement to HTML as it is a software- and hardware-independent tool for carrying information.
• difference between XML and HTML:
• 
  

XML	HTML
Designed to transport data, with focus on what data is.	Design to display data with focus on how data looks looks.
About displaying information.	About carrying information.

How can XML be used?

• used widely in aspects of web development often to simplify data storage and sharing.
• XML separates data from HTML.
1. data can be stored in separate XML files.
2. with a few lines of JavaScript, you can read an external XML files and update the data content without interrupt the HTML data.
• since  data is stored in text format, thus easier to expand or upgrade to new operating system, new applications, or new browsers, without losing data.
• Foundation for several next-gen Web technologies sucg as XHTML, WSDL, WAP. WML, RSS, RDF, OWL and SMIL.
• XML documents form a tree structure that start at "the root"and branched to "the leaves"

• An example of XML data:

The syntax Rules:

• All element must have a closing tag.

• XML tag are case sensitive, thus tag <Letter> is different with tag <letter>.
• Opening and closing tags must be written with the same case.

• XML must be properly nested within each other. If you compare the XML with HTML, XML are properly nested within each other.

XML	HTML
<b><i>This text is bold and italic</i></b> -properly nested	<b><i>This text is bold and italic</b></i> -not properly nested.

• must contain one element called parent. This element is called root element.

• just like HTML, XML also can have attributes in name/value pair just like in HTML, and must always be quoted.

The predefined entity references in XML:

Command	Explanation
<!-- This is a comment -->	comment in XML which is  similar to HTML command.
HTML:Hello            my name is Tove Output: Hello my name is Tove	XML white-space in a document is not  truncated. However, in  HTML, multiple white-space truncates the character to one single white-space.

• new line is stored depend on the type of operating system used:

Type of operating system applications	How XML store a new line
Windows applications	stored as a pair of characters: carriage return (CR) line feed (LF)
Unix applications	stored as a line feed character (LF)
Macintosh applications	use only a carriage return (CR) character to store a new line.

XML Element

• An XML element is everything from (including) the element's start tag to (include) the element's end tag.
• can contain other elements, simple text or a mixture of both.
• can also have attributes.

Example of the XML element.

• from the example above, only book have attribute (catogery="CHILDREN")

XML Naming Rules:

• can contain letters, numbers, and other characters.
• cannot start with number or punctuation character.
• cannot start with xml.

XML extensible:

• XML element can be extended to carry more information.

XML Attributes

• XML attributes must always be quoted either single or double quote, both can be used.
• an example:

                            <person sex="female">    or      <person sex='female'>

• if the attribute value itself contain double quotes you can use single quotes, an example:

<gangster name='George "Shotgun" Ziegler'>   or  <ganster name="George &quot;Shotgun&quot; Ziegler">

XML validation

• XML with correct syntax is "Well Formed" XML
1. document must have root element ,
2. element must have closing tag, 
3. tag must case sensitive,
4. element must properly nested,
5. Attribute must quoted.
• XML validated against a DTD is a "Valid" XML

That's all about XML, for more detail, please do visit http://www.w3schools.com/xml/