private void Form1_Load(object sender, System.EventArgs e)
        {
            const string schemaPath = @"c:\AddressBook.xsd";
            const string documentPath = @"c:\sample001.xml";
            XmlDocument doc = new XmlDocument();
            XmlValidatingReader reader = new XmlValidatingReader(
                new XmlTextReader( documentPath ) );
            reader.Schemas.Add( null, schemaPath );
            reader.ValidationType = ValidationType.Schema;
            doc.Load( reader );
        }