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XML Schema


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".

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


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








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.

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


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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Reference: https://www.w3schools.com/xml/xml_schema.asp