<?xml version="1.0"?>
<xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema">

   <!-- Define the complex type product. -->
   <xsd:complexType name="product">
      <xsd:sequence>
         <xsd:element name="productName" type="xsd:string"/>
         <xsd:element name="productPrice" type="xsd:decimal"/>
         <xsd:element name="inStock" type="xsd:boolean"/>
      </xsd:sequence>
      <xsd:attribute name="id" type="xsd:integer"/>
   </xsd:complexType>

   <!-- This is the structure the document must match.
        It begins with a productCatalog element that nests other elements. -->
   <xsd:element name="productCatalog">
      <xsd:complexType>
         <xsd:sequence>
            <xsd:element name="catalogName" type="xsd:string"/>
            <xsd:element name="expiryDate" type="xsd:date"/>

            <xsd:element name="products">
               <xsd:complexType>
                  <xsd:sequence>
                     <xsd:element name="product" type="product"
                      maxOccurs="unbounded" />
                  </xsd:sequence>
               </xsd:complexType>
            </xsd:element>
         </xsd:sequence>
      </xsd:complexType>
   </xsd:element>



</xsd:schema>






<?xml version="1.0" ?>
<productCatalog>
    <catalogName>Acme Fall 2003 Catalog</catalogName>
    <expiryDate>Jan 1, 2004</expiryDate>

    <products>
        <product id="1001">
            <productName>Magic Ring</productName>
            <productPrice>$342.10</productPrice>
            <inStock>true</inStock>
        </product>
        <product id="1002">
            <productName>Flying Carpet</productName>
            <productPrice>982.99</productPrice>
            <inStock>Yes</inStock>
        </product>
    </products>
</productCatalog>

The next example shows a utility class that displays all errors in an XML document when the 
ValidateXml method is called. Errors are displayed in a console window, and a final Boolean 
variable is returned to indicate the success or failure of the entire validation operation. 
using System;
using System.Xml;
using System.Xml.Schema;

public class ConsoleValidator {

    // Set to true if at least one error exists.
    private bool failed;

    public bool Failed {
        get {return failed;}
    }

    public bool ValidateXml(string xmlFilename, string schemaFilename) {

        // Create the validator.
        XmlTextReader r = new XmlTextReader(xmlFilename);
        XmlValidatingReader validator = new XmlValidatingReader(r);
        validator.ValidationType = ValidationType.Schema;

        // Load the schema file into the validator.
        XmlSchemaCollection schemas = new XmlSchemaCollection();
        schemas.Add(null, schemaFilename);
        validator.Schemas.Add(schemas);

        // Set the validation event handler.
        validator.ValidationEventHandler += 
          new ValidationEventHandler(ValidationEventHandler);
            
        failed = false;
        try {

            // Read all XML data.
            while (validator.Read())
            {}
        }catch (XmlException err) {

            // This happens if the XML document includes illegal characters
            // or tags that aren't properly nested or closed.
            Console.WriteLine("A critical XML error has occurred.");
            Console.WriteLine(err.Message);
            failed = true;
        }finally {
            validator.Close();
        }

        return !failed;
    }

    private void ValidationEventHandler(object sender, 
      ValidationEventArgs args) {

        failed = true;

        // Display the validation error.
        Console.WriteLine("Validation error: " + args.Message);
        Console.WriteLine();
    }
}
Here's how you would use the class to validate the product catalog:
using System;

public class ValidateXml {

    private static void Main() {

        ConsoleValidator consoleValidator = new ConsoleValidator();
        Console.WriteLine("Validating ProductCatalog.xml.");

        bool success = consoleValidator.ValidateXml("ProductCatalog.xml",
          "ProductCatalog.xsd");
        if (!success) {
            Console.WriteLine("Validation failed.");
        }else {
            Console.WriteLine("Validation succeeded.");
        }

        Console.ReadLine();
    }
}


the result：
Validating ProductCatalog_Invalid.xml.

Validation error: The 'expiryDate' element has an invalid value according to
 its data type. [path information truncated] 

Validation error: The 'productPrice' element has an invalid value according to
 its data type. [path information truncated]

Validation error: The 'inStock' element has an invalid value according to its
 data type. [path information truncated]

Validation failed.


Finally, if you want to validate an XML document and then process it, you can use 
XmlValidatingReader to scan a document as it's read into an in-memory XmlDocument. 
Here's how it works:
XmlDocument doc = new XmlDocument();
XmlTextReader r = new XmlTextReader("ProductCatalog.xml");
XmlValidatingReader validator = new XmlValidatingReader(r);

// Load the schema into the validator.
validator.ValidationType = ValidationType.Schema;
XmlSchemaCollection schemas = new XmlSchemaCollection();
schemas.Add(null, "ProductCatalog.xsd");
validator.Schemas.Add(schemas);

// Load the document and validate it at the same time.
// Don't handle the ValidationEventHandler event. Instead, allow any errors
/// to be thrown as an XmlSchemaException.
try {
    doc.Load(validator);
    // (Validation succeeded if you reach here.)
}catch (XmlSchemaException err) {
    // (Validation failed if you reach here.)
}