XML Namespaces

[Murali Mohan]

Hai,
I have some code with XML schemas with namespaces.I have understood the schema structure but I couldn't understand about namespaces.Following is the code.
<?xml version="1.0"?>
<xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema"
targetNamespace="http://www.books.org"
xmlns="http://www.books.org"
elementFormDefault="qualified">
<xsd:element name="BookStore">
<xsd:complexType>
<xsd:sequence>
<xsd:element ref="Book" minOccurs="1" maxOccurs="unbounded"/>
</xsd:sequence>
</xsd:complexType>
</xsd:element>
<xsd:element name="Book">
<xsd:complexType>
<xsd:sequence>
<xsd:element ref="Title" minOccurs="1" maxOccurs="1"/>
<xsd:element ref="Author" minOccurs="1" maxOccurs="1"/>
<xsd:element ref="Date" minOccurs="1" maxOccurs="1"/>
<xsd:element ref="ISBN" minOccurs="1" maxOccurs="1"/>
<xsd:element ref="Publisher" minOccurs="1" maxOccurs="1"/>
</xsd:sequence>
</xsd:complexType>
</xsd:element>
<xsd:element name="Title" type="xsd:string"/>
<xsd:element name="Author" type="xsd:string"/>
<xsd:element name="Date" type="xsd:string"/>
<xsd:element name="ISBN" type="xsd:string"/>
<xsd:element name="Publisher" type="xsd:string"/>
</xsd:schema>
In the code What is targetNamespace?What is use?
What is xmlns?What is use?
What is elementFormDefault?

[Ajith Kallambella]

The idea is that when you are dealing with XML documents from ten different (external) sources, name collisions can occur. If you use namespaces, you are distinguishing one element from another based on the namespace prefix. myNameSpace:Employee is not the same as yourNameSpace:Employee. When you delcare a namespace you also give it an unique URI ( Universal Resource Identifier ).
Checkout the Namespace FAQ which is one of my favourite resources.

Good luck,

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Ajith Kallambella M.
Sun Certified Programmer for the Java�2 Platform.
IBM Certified Developer - XML and Related Technologies, V1.