• Derived from Standard Generalized Markup Language
• Software and Hardware Independent
• Used for Storing and transporting data
• Self-descriptive
• W3C (World Wide Web Consortium) Recommendation

Characteristics

• Extensibility: Create new self-descriptive tags or language.
• Functional: Used not to present but to store.
• Standard: It has an open standard recommended by W3C

Applications

• Simplify creation of HTML documents
• Exchange Information
• Offloading and reloading databases
• Merged with Style Sheets to create any desired output

Differences between XML and HTML

Syntax

<?xml version="1,0"?>
<contact_info>
    <name>Nancy</name>
    <company>Arkade</company>
    <phone> 8506025748 </phone>
</contact_info>

Two kinds of information: Markup(contact_info), Text(Nancy)

XML Declaration

<?xml version="1.0" encoding="UTF-8"?>

Here, version is the XML version and encoding is the character encoding used.

XML Declaration is case sensitive. "<?xml>" must be written as is.

It should be the first line of the document.

An HTTP protocol can override the value of encoding specified.

Tags and Elements

• enclosed in triangular brackets < >

• Should be closed either by a closing tag or by adding / to the opening tag.

• Can contain multiple XML-Elements as its children. Children must not overlap.

Root Element

A document can have only one root element.

<root> 
    <x></x>
    <y></y>
</root>

Case Sensitivity

Tags are case sensitive. The opening and closing tags must be in exactly the same case.

Attributes

A property of an element, in the form of a name/value pair.

• case-sensitive
• an element cannot have two attributes with the same name
• attribute name is written without quotation marks, values are always written with quotation marks.

XML References

Used to add additional text or markup in a document.

• begin with an & and end with ;. Two types of references:
  • Entity References: contains a name.
  • Character References: contains a hash and a number.

XML Text

• Whitespaces are ignored.
• Some characters are reserved by xml and therefore cannot be used directly. Entities can be used instead.

XML Namespaces

Solves conflicts between different xml documents used together.

xmlns attribute can be used int the starting tag of an element.

<root> 
<h:element xmlns:h="http://www.w3.org/TR/html4/">
    <h:subelement />
</h:element>

<f:element xmlns:f="http://www.w3.org/TR/furniture">
</f:element>
</root>

XML Validator

A “valid” XML docuement must be well-formed(follow syntax rules ) and it must conform to a document type definition.

There are 2 different document type definitions:

• DTD - The original Document Type Definition
• XML Schema - An xml0based alternative to DTD

DTD

<!DOCTYPE book [
<!ELEMENT book (title, author, price)>
<!ELEMENT title (#PCDATA)>
<!ELEMENT author (#PCDATA)>
<!ELEMENT price (#PCDATA)> 
]>

The document type is book. The book element must contain title, author and price. title, author and price require to be of type “#PCDATA”(Parse-able Character Data)

DTDs can be internal or external.

• Internal DTDs are defined just after the XML Definition.
• External DTD are sourced from another file.

<!DOCTYPE student SYSTEM "external.dtd">

Applications of DTD:

• Independent groups of people can agree to use a standard DTD.
• To verify own data.

XML Schema

Alternative to DTD, xml-based.

<xs:schema>
    <xs:element name="elementName">
        <xs:complexType>
            <xs:sequence>
                <xs:element name="title" type="xs:string"/>
                <xs:element name="author" type="xs:string"/>
            </xs:sequence>
        </xs:complexType>
    </xs:element>
</xs:schema>

the element book is a complexType i.e. root.

Can be saved as schema.xsd and imported

<student xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.w3schools.com student.xsd"> 

XSLT

XSL - Extensible Stylesheet Language XSLT - XSL Transformations

• XSLT transforms XML into another XML document
• XSLT uses XPath to navigate in XML documents
• XSLT is a W3C recommendation

<?xml-stylesheet type="text/xsl" href="book.xsl"?>

<?xml version="1.0" encoding="UTF-8"?><xsl:stylesheet version="1.0" xmlns:xls="http://www.w3.org/1999/XSL/Transform"><xsl:template match="/">
<html>
    <body>
        <h2>Book Details</h2>
        <table border="1">
            <tr>
                <th>Title</th>
                <th>Author</th>
            </tr>
            <xsl:for-each select="book_store/book">
                <tr>
                    <td><xsl:value-of select="title" /></td>
                    <td><xsl:value-of select="author"/></td>
                </tr>
            </xsl:for-each>
        </table>
    </body>
</html>
</xsl:template>
</xsl:stylesheet>