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XML
EXtensible Markup Language

Introduction

Definition
 XML stands for EXtensible Markup
Language
 XML is a markup language much like HTML
 XML was designed to carry data, to
transport and store data, not to display data
 XML tags are not predefined. You must
define your own tags
 XML is designed to be self-descriptive
The best description of XML is: “XML is a
software and hardware-independent tool for
carrying information”.

XML & HTML
 XML is not a replacement for HTML.
 XML and HTML were designed with
different goals:
◦ XML was designed to transport and store
data, with focus on what data is
◦ HTML was designed to display data, with
focus on how data looks
◦ HTML is about displaying
information, while XML is about carrying
information.

First Example
<note>
<to>Tove</to>
<from>Jani</from>
<heading>Reminder</heading>
<body>Don't forget me this weekend!</body>
</note>

 The note above is quite self-descriptive.
It has sender and receiver
information, it also has a heading and a
message body.

XML Tags
 The tags in the example above (like <to>
and <from>) are not defined in any XML
standard. These tags are "invented" by the
author of the XML document.
 That is because the XML language has no
predefined tags.
 The tags used in HTML are predefined.
HTML documents can only use tags defined
in the HTML standard (like <p>, <h1>, etc.).
 XML allows the author to define his/her own
tags and his/her own document structure.

XML Main Features
XML Simplifies Data Transport

Exchanging data as XML greatly reduces this
complexity, since the data can be read by different
incompatible applications.

JAVA
PHP

DOC.
XML

.NET

XML Separates Data from HTML

If you need to display dynamic data in your HTML
document, it will take a lot of work to edit the HTML each time
the data changes.

With XML, data can be stored in separate XML files. This way
you can concentrate on using HTML/CSS for display and
layout, and be sure that changes in the underlying data will
not require any changes to the HTML..

XML Makes Your Data More Available
Different applications can access your data, not only in
HTML pages, but also from XML data sources.

With XML, your data can be available to all kinds of "reading
machines" (Handheld computers, voice machines, news
feeds, etc), and make it more available for blind people, or
people with other disabilities.

XML Simplifies Platform Changes

XML data is stored in text format. This makes it
easier to expand or upgrade to new operating
systems, new applications, or new
browsers, without losing data.

XML Simplifies Data Sharing

In the real world, computer systems and
databases contain data in incompatible formats.

XML Tree
 XML documents form a tree structure that
starts at "the root" and branches to "the
leaves".

Tree Structure
 XML documents must contain a root element. This
element is "the parent" of all other elements.
 The elements in an XML document form a
document tree. The tree starts at the root and
branches to the lowest level of the tree.
 All elements can have sub elements (child
elements).
<root>
<child>
<subchild attribute=”value”>.....</subchild>
</child>
</root>

XML Syntax Rules
 All XML Elements Must Have a Closing Tag.
 XML Tags are Case Sensitive.
 XML Elements Must be Properly Nested.
 XML Documents Must Have a Root Element.
 XML Attribute Values Must be Quoted.

<root>
<child>
<subchild attribute=”value”>value #1</subchild>
</child>
</root>

XML Elements
 An XML element is everything from
(including) the element's start tag to
(including) the element's end tag.
An element can contain:

◦ other elements
◦ text
◦ attributes
◦ or a mix of all of the above...

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

XML Elements are Extensible
• XML elements can be extended to carry more
information.
<note>
<to>Tove</to>
<from>Jani</from>
<body>Don't forget me this
weekend!</body>
</note>

<note>
<date>2008-01-10</date>
<to>Tove</to>
<from>Jani</from>
<heading>Reminder</heading>
<body>Don't forget me this
weekend!</body>
</note>

XML Attributes
 XML elements can have attributes, just like HTML.
 Attributes provide additional information about an
element.
 In HTML, attributes provide additional information
about elements:
<img src=/slideshow/xml-intro1/14579383/"computer.gif">
<a href="demo.asp">
 In the example below, the file type is irrelevant to
the data, but can be important to the software that
wants to manipulate the element:
<file type="gif">computer.gif</file>

XML Attributes Must be
Quoted
 Either single or double quotes can be used. For a person's
sex, the person element can be written like this:
<person sex="female">

 or like this:
<person sex='female'>

 If the attribute value itself contains double quotes you can use
single quotes, like in this example:

<gangster name='George "Shotgun" Ziegler'>

 or you can use character entities:
<gangster name="George " Shotgun" Ziegler">

XML Elements vs. Attributes
<person sex="female"> Attribute
<firstname>Anna</firstname>
<lastname>Smith</lastname>
</person>

<person>
<sex>female</sex> Element
<firstname>Anna</firstname>
<lastname>Smith</lastname>
</person>

*Authors recommends use as Elements

Using XML Attributes
 Some of the problems with using attributes are:
◦ attributes cannot contain multiple values (elements can)
◦ attributes cannot contain tree structures (elements can)
◦ attributes are not easily expandable (for future changes)

 Attributes are difficult to read and maintain. Use
elements for data. Use attributes for information that is
not relevant to the data.

Example using only attributes:

<note day="10" month="01" year="2008"
to="Tove" from="Jani" heading="Reminder"
body="Don't forget me this weekend!“>

</note>

XML Validation
XML with correct syntax is "Well Formed" XML.

• A "Well Formed" XML document has
correct XML syntax.
• Use the correct syntax rules.
• XML documents must have a root element

• XML elements must have a closing tag
• XML tags are case sensitive
• XML elements must be properly nested
• XML attribute values must be quoted

XML validated against a DTD is "Valid"
XML.

• A "Valid" XML document is a "Well Formed" XML
document, which also conforms to the rules of a
Document Type Definition (DTD)

The purpose of a DTD is to define the structure
of an XML document. It defines the structure
with a list of legal elements:

<!DOCTYPE note

XML DTD [
<!ELEMENT note
(to,from,heading,body)>
<!ELEMENT to (#PCDATA)>
<!ELEMENT from (#PCDATA)>
<!ELEMENT heading (#PCDATA)>
<!ELEMENT body (#PCDATA)>
]>

W3C supports an XML-based alternative to
DTD:
<xs:element name="note">

XML <xs:complexType>
<xs:sequence>
<xs:element name="to" type="xs:string"/>
Schema <xs:element name="from" type="xs:string"/>
<xs:element name="heading" type="xs:string"/>
<xs:element name="body" type="xs:string"/>
</xs:sequence>
</xs:complexType>
</xs:element>

Viewing XML Files
 Raw XML files can be viewed in all
major browsers.
 If an erroneous XML file is
opened, the browser will report the
error.
 The XML document will be displayed
with color-coded root and child
elements. A plus (+) or minus sign (-)
to the left of the elements can be
clicked to expand or collapse the

Displaying XML with CSS
 With CSS (Cascading Style Sheets)
you can add display information to an
XML document.
 It is possible to use CSS to format an
XML document.
 Let’s see an example of how to use a
CSS style sheet to format an XML
document.

THANKS…… And let’s build together
some XML 

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