XML Schema

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An XML Schema describes the structure of an XML document, just like a DTD.

An XML document with correct syntax is called "Well Formed".

An XML document validated against an XML Schema is both "Well Formed" and "Valid".

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XML Schema

XML Schema is an XML-based alternative to DTD:

<xs:element name="note">

<xs:complexType>
  <xs:sequence>
    <xs:element name="to" type="xs:string"/>
    <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>

The Schema above is interpreted like this:

• <xs:element name="note"> defines the element called "note"
• <xs:complexType> the "note" element is a complex type
• <xs:sequence> the complex type is a sequence of elements
• <xs:element name="to" type="xs:string"> the element "to" is of type string (text)
• <xs:element name="from" type="xs:string"> the element "from" is of type string
• <xs:element name="heading" type="xs:string"> the element "heading" is of type string
• <xs:element name="body" type="xs:string"> the element "body" is of type string

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XML Schemas are More Powerful than DTD

• XML Schemas are written in XML
• XML Schemas are extensible to additions
• XML Schemas support data types
• XML Schemas support namespaces

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Why Use an XML Schema?

With XML Schema, your XML files can carry a description of its own format.
With XML Schema, independent groups of people can agree on a standard for interchanging data.
With XML Schema, you can verify data.

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XML Schemas Support Data Types

One of the greatest strengths of XML Schemas is the support for data types:

• It is easier to describe document content
• It is easier to define restrictions on data
• It is easier to validate the correctness of data
• It is easier to convert data between different data types

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XML Schemas use XML Syntax

Another great strength about XML Schemas is that they are written in XML:

• You don't have to learn a new language
• You can use your XML editor to edit your Schema files
• You can use your XML parser to parse your Schema files
• You can manipulate your Schemas with the XML DOM
• You can transform your Schemas with XSLT

If you want to study XML Schema, please read our XML Schema Tutorial.

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