XSD - Syntax

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An XML XSD is kept in a separate document and then the document can be linked to an XML document to use it.

Syntax

The basic syntax of a XSD is as follows −

<?xml version = "1.0"?>

<xs:schema xmlns:xs = "http://www.w3.org/2001/XMLSchema">
   targetNamespace = "http://www.howcodex.com"
   xmlns = "http://www.howcodex.com" elementFormDefault = "qualified">
   
   <xs:element name = 'class'>
      <xs:complexType>
         <xs:sequence>
            <xs:element name = 'student' type = 'StudentType' minOccurs = '0' 
               maxOccurs = 'unbounded' />
         </xs:sequence>
      </xs:complexType>
   </xs:element>

   <xs:complexType name = "StudentType">
      <xs:sequence>
         <xs:element name = "firstname" type = "xs:string"/>
         <xs:element name = "lastname" type = "xs:string"/>
         <xs:element name = "nickname" type = "xs:string"/>
         <xs:element name = "marks" type = "xs:positiveInteger"/>
      </xs:sequence>
      <xs:attribute name = 'rollno' type = 'xs:positiveInteger'/>
   </xs:complexType>
   
</xs:schema>

<Schema> Element

Schema is the root element of XSD and it is always required.

<xs:schema xmlns:xs = "http://www.w3.org/2001/XMLSchema">

The above fragment specifies that elements and datatypes used in the schema are defined in http://www.w3.org/2001/XMLSchema namespace and these elements/data types should be prefixed with xs. It is always required.

targetNamespace = "http://www.howcodex.com"

The above fragment specifies that elements used in this schema are defined in http://www.howcodex.com namespace. It is optional.

xmlns = "http://www.howcodex.com"

The above fragment specifies that default namespace is http://www.howcodex.com.

elementFormDefault = "qualified"

The above fragment indicates that any elements declared in this schema must be namespace qualified before using them in any XML Document.It is optional.

Referencing Schema

Take a look at the following Referencing Schema −

<?xml version = "1.0"?>

<class xmlns = "http://www.howcodex.com"
   xmlns:xsi = "http://www.w3.org/2001/XMLSchema-instance"
   xsi:schemaLocation = "http://www.howcodex.com student.xsd">  
   
   <student rollno = "393">    
      <firstname>Dinkar</firstname>
      <lastname>Kad</lastname>
      <nickname>Dinkar</nickname>
      <marks>85</marks>
   </student>
   
   <student rollno = "493">	 
      <firstname>Vaneet</firstname>
      <lastname>Gupta</lastname>
      <nickname>Vinni</nickname>
      <marks>95</marks>
   </student>
   
   <student rollno = "593">    
      <firstname>Jasvir</firstname>
      <lastname>Singh</lastname>
      <nickname>Jazz</nickname>
      <marks>90</marks>
   </student>
</class>

xmlns = "http://www.howcodex.com"

The above fragment specifies default namespace declaration. This namespace is used by the schema validator check that all the elements are part of this namespace. It is optional.

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

After defining the XMLSchema-instance xsi, use schemaLocation attribute. This attribute has two values, namespace and location of XML Schema, to be used separated by a space. It is optional.

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