Document type definition (DTD) validation is implemented using the validity constraints defined in the World Wide Web Consortium (W3C) Extensible Markup Language (XML) 1.0 Recommendation. DTDs use a formal grammar to describe the structure and syntax of compliant XML documents; they specify content and values allowed for the XML document.

To perform validation against a DTD, the XmlReader uses the DTD defined in the DOCTYPE declaration of an XML document. The DOCTYPE declaration can either point to an inline DTD or can be a reference to an external DTD file.

• Set the System.Xml.XmlReaderSettings.ProhibitDtd property to false.

• Set the System.Xml.XmlReaderSettings.ValidationType property to ValidationType.DTD.

• If the DTD is an external file stored on a network resource that requires authentication, pass an XmlResolver object with the necessary credentials to the Create method.

Example

using System;
using System.Xml;
using System.Xml.Schema;
using System.IO;

public class Sample {

  public static void Main() {

    // Set the validation settings.
    XmlReaderSettings settings = new XmlReaderSettings();
    settings.ProhibitDtd = false;
    settings.ValidationType = ValidationType.DTD;
    settings.ValidationEventHandler += new ValidationEventHandler (ValidationCallBack);
 
    // Create the XmlReader object.
    XmlReader reader = XmlReader.Create("itemDTD.xml", settings);


    // Parse the file. 
    while (reader.Read());
    
  }

  // Display any validation errors.
  private static void ValidationCallBack(object sender, ValidationEventArgs e) {
    Console.WriteLine("Validation Error: {0}", e.Message);
  }
}

<!--XML file using a DTD-->
<!DOCTYPE store [
  <!ELEMENT store (item)*> 
  <!ELEMENT item (name,dept,price)>
  <!ATTLIST item type CDATA #REQUIRED>
  <!ELEMENT name (#PCDATA)>
  <!ELEMENT price (#PCDATA)>]>
<store>
  <item type="supplies"  ISBN="2-3631-4">
    <name>paint</name>
    <price>16.95</price>
  </item>
</store>

See Also